Jose ´ Maria ´ Bermu ´ dez de Castro, Antonio Rosas & Marı ´a Elena Nicola ´s Museo Nacional de Ciencias Naturales, C.S.I.C., Jose ´ Gutie ´rrez Abascal 2, 28006 Madrid, Spain Received 20 December 1997 Revision received 16 March 1999 and accepted 25 April 1999 Keywords: Gran Dolina, Atapuerca, Lower Pleistocene, teeth. Dental remains from Atapuerca-TD6 (Gran Dolina site, Burgos, Spain) A descriptive and comparative study of the human dental remains recovered from level six (Aurora stratum) of the Gran Dolina (TD) site, Sierra de Atapuerca, northern Spain, is presented. The TD6 dental sample consists of two deciduous and 28 permanent teeth, belonging to a minimum of six individuals. Paleomagnetic analyses of the TD sequence suggest an age for the Aurora stratum of greater than 780 ka. The associated fossil macro- and micrommals are consistent with a date for the Atapuerca-TD6 hominids at the end of the Early Pleistocene. As a whole, the size of the TD6 teeth is large and comparable to that of the African Lower Pleistocene hominids. Most morphological dental traits are plesiomorphic for the genus Homo, whereas the shape analysis has revealed some size-related trends that differ from those seen in early Homo. Thus, the relative size increase of the maxillary and mandibular anterior teeth and buccolingual diameter of the first molars, the reduction of the third molars and lower canines, and the P 3 >P 4 size sequence are all characteristic of the population represented by the TD6 hominids. The morphological evidence suggests that the TD6 hominids are closer to African Lower and early Middle Pleistocene hominids than they are to European Middle Pleistocene hominids. However, some dental traits of the TD6 hominids, such as the expansion of the anterior teeth, the P 3 >P 4 size sequence, and the morphology of the lower canine also suggest an evolutionary continuity between the population represented by these hominids and the European Middle Pleistocene population. Furthermore, dental evidence indicates that the TD6 hominids are clearly distinct from Asian H. erectus. Dental evidence also suggests that the TD6 hominids could represent an evolutionary connection between H. ergaster and H. heidelbergensis. ? 1999 Academic Press Journal of Human Evolution (1999) 37, 523–566 Article No. jhev.1999.0323 Available online at http://www.idealibrary.com on Introduction The Sierra de Atapuerca is situated about 0)10*E and 42)20*N. It is near the Arlanzo ´n river and 14 km east from the city of Burgos, northern Spain. A disused railway traverses into the southwestern slope of the Sierra de Atapuerca, where some fissure-fill Pleisto- cene deposits of three main karstic cavities are exposed in a cutting (Carbonell et al., 1998). One of these deposits, Gran Dolina (TD), has outcrops up to 18 m deep. The TD site fills the cavity catalogued as BU-IV- A-16 (Martin et al., 1981). A total of 11 lithological levels, numbered 1–11 from bottom to top, can be distinguished in TD (see Pare ´s & Pe ´rez-Gonza ´lez, 1995). Exca- vation of a 6 m 3 (2·5 #2·5) planar section was begun in 1993. In July of 1994, excava- tion reached level 6 (TD6), and one of the TD6 strata, the so-called Aurora stratum, yielded a rich faunal and lithic assemblage (Carbonell et al., 1995). Included in this assemblage were more than 30 human fossil remains. The top of the Aurora stratum is about 1 m below the Matuyama/Brunhes boundary (Pare ´s & Pe ´rez-Gonza ´lez, 1995). Excavation of the Aurora stratum (6 m 2 ) 0047–2484/99/090523+44$30.00/0 ? 1999 Academic Press
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Jose Maria Bermudezde Castro, AntonioRosas & Marıa ElenaNicolasMuseo Nacional de CienciasNaturales, C.S.I.C.,Jose Gutierrez Abascal 2,28006 Madrid, Spain
Received 20 December1997Revision received 16 March1999and accepted 25 April 1999
Keywords: Gran Dolina,Atapuerca, LowerPleistocene, teeth.
Dental remains from Atapuerca-TD6(Gran Dolina site, Burgos, Spain)
A descriptive and comparative study of the human dental remainsrecovered from level six (Aurora stratum) of the Gran Dolina (TD)site, Sierra de Atapuerca, northern Spain, is presented. The TD6dental sample consists of two deciduous and 28 permanent teeth,belonging to a minimum of six individuals. Paleomagnetic analyses ofthe TD sequence suggest an age for the Aurora stratum of greaterthan 780 ka. The associated fossil macro- and micrommals areconsistent with a date for the Atapuerca-TD6 hominids at the end ofthe Early Pleistocene. As a whole, the size of the TD6 teeth is largeand comparable to that of the African Lower Pleistocene hominids.Most morphological dental traits are plesiomorphic for the genusHomo, whereas the shape analysis has revealed some size-relatedtrends that differ from those seen in early Homo. Thus, the relativesize increase of the maxillary and mandibular anterior teeth andbuccolingual diameter of the first molars, the reduction of the thirdmolars and lower canines, and the P3>P4 size sequence are allcharacteristic of the population represented by the TD6 hominids.The morphological evidence suggests that the TD6 hominids arecloser to African Lower and early Middle Pleistocene hominids thanthey are to European Middle Pleistocene hominids. However, somedental traits of the TD6 hominids, such as the expansion of theanterior teeth, the P3>P4 size sequence, and the morphology ofthe lower canine also suggest an evolutionary continuity between thepopulation represented by these hominids and the European MiddlePleistocene population. Furthermore, dental evidence indicates thatthe TD6 hominids are clearly distinct from Asian H. erectus. Dentalevidence also suggests that the TD6 hominids could represent anevolutionary connection between H. ergaster and H. heidelbergensis.
? 1999 Academic Press
Journal of Human Evolution (1999) 37, 523–566Article No. jhev.1999.0323Available online at http://www.idealibrary.com on
Introduction
The Sierra de Atapuerca is situated about0)10*E and 42)20*N. It is near the Arlanzonriver and 14 km east from the city of Burgos,northern Spain. A disused railway traversesinto the southwestern slope of the Sierra deAtapuerca, where some fissure-fill Pleisto-cene deposits of three main karstic cavitiesare exposed in a cutting (Carbonell et al.,1998). One of these deposits, Gran Dolina(TD), has outcrops up to 18 m deep. TheTD site fills the cavity catalogued as BU-IV-A-16 (Martin et al., 1981). A total of 11
0047–2484/99/090523+44$30.00/0
lithological levels, numbered 1–11 frombottom to top, can be distinguished in TD(see Pares & Perez-Gonzalez, 1995). Exca-vation of a 6 m3 (2·5#2·5) planar sectionwas begun in 1993. In July of 1994, excava-tion reached level 6 (TD6), and one of theTD6 strata, the so-called Aurora stratum,yielded a rich faunal and lithic assemblage(Carbonell et al., 1995). Included in thisassemblage were more than 30 human fossilremains. The top of the Aurora stratum isabout 1 m below the Matuyama/Brunhesboundary (Pares & Perez-Gonzalez, 1995).Excavation of the Aurora stratum (6 m2)
? 1999 Academic Press
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finished in 1996. After sorting the fossilsrecovered from this stratum, a total of85 human remains were identified. TheTD6 human sample includes postcranial(Carretero et al., 1999; Lorenzo et al.,1999), facial and neurocranial (Arsuagaet al., 1999), mandibular (Rosas &Bermudez de Castro, 1999), and dentalspecimens.
Because of a unique combination ofcranial, dental, and mandibular traits in thecurrent TD6 hypodigm we have named anew Homo species, H. antecessor, to includethese human fossil remains (Bermudez deCastro et al., 1997). In this paper it wassuggested that the new species couldrepresent the last common ancestor of theNeandertals and modern humans. That is,H. antecessor would have an Afro-Europeandistribution, and would be the origin oftwo evolutionary lineages, one of themexclusively European and formed by twochronospecies, H. heidelbergensis and H.neanderthalensis, whereas the other led to H.sapiens, probably in the African continent.Previous information concerning dental
remains from TD6 were published inCarbonell et al. (1995) and Bermudez deCastro et al. (1997). The aim of this paper isto present a detailed morphological andmetrical comparative analysis of these dentalremains. A discussion of the phylogeneticrelationships of the TD6 hominids withregard to the information offered by thedental remains is also presented.
List of the mandibular, maxillary and dental remains from the TD6 Aurorastratum
Inventory number Specimen Hominid
ATD6-5 Right mandible fragment (M1–M3) ATD6-13 Left maxillary fragment (C–P3) ATD6-1 Left lower C ATD6-2 Left I2 ATD6-3 Right P3 ATD6-4 Right P4 ATD6-6 Fragment of crown of right lower C H1ATD6-7 Right P3 ATD6-8 Right P4 ATD6-9 Left P4 ATD6-10 Right M1 ATD6-11 Left M1 ATD6-12 Right M2 ATD6-14 Left maxillary fragment (dc–dm1) H2ATD6-69 Maxilla and left zygomatic bone
(left P3, M1, and unerupted M2, M3 and right I2–M1)H3
ATD6-48 Left I2 H4ATD6-52 Left I1 H5ATD6-312 Left I2 germ H6
Table 1
TD6 dental remains
The dental sample from the Aurora stratumfrom TD6 belongs to a minimum of sixindividuals (Table 1). The Hominid 1 (H1)is represented by a fragment of the rightside of a mandible (Rosas & Bermudez deCastro, 1999) with M1, M2, and uneruptedM3, a small and poorly preserved maxillaryfragment with the left C and P3, as well aseleven isolated teeth. Hominid 2 (H2) isrepresented by part of a left infant maxilla,retaining dc–dm1. The radiographic imageof this specimen shows the uneruptedcrowns of permanent teeth. A well preservedsubadult maxilla, with the left frontal
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process and the left zygomatic bone, formsHominid 3 (H3). This specimen also pre-serves in situ the left P3, M1, and uneruptedM2 and M3, as well as the right I2, C, P3, P4,and M1. Two moderately worn left I1 and I2,which do not fit to each other, represent theevidence of two additional adult dentitionsin the TD6 human sample (H4 and H5).Finally, the germ of a left I2 is evidence ofanother infant individual (H6). Details ofthe pattern of dental development and anassessment of the physiological age of thesubadult hominids from TD6 will form thesubject of a future paper.
Methods
We provide in this paper descriptions of themorphology of the TD6 teeth, indicating themain morphological traits of each specimen.In order to facilitate the understanding ofthese descriptions, photographs of the teethare also included.
The mesiodistal (MD) and buccolingual(BL) dimensions of the Atapuerca-TD6teeth were recorded to the nearest 0·1 mmfollowing the technique proposed byFlechier (1975). A caliper with wide, flatand pointed tips, which allowed insertionbetween teeth still in situ, was used. Thecomputed crown area (CCA=MD#BL)was calculated from these tooth dimensions.When the root (anterior teeth), or at leastone element of the root complex (postcanineteeth), was complete, the maximum rootlength (RL) was also recorded, following thetechnique described in Bermudez de Castro(1988). The surface area of the crowns ofthe TD6 premolars and molars, as well asthe areas of the major cusps of these teeth,were measured from occlusal photographs.Each specimen was oriented so that theocclusal plane was perpendicular to the opti-cal axis of a camera fitted up with a Tamron90 mm F 2·5 lens and a Tamron extensiontube 18F. In order to get a maximum depthof field, an aperture of f/32 was set. The
magnification ratio was adjusted to 1:1, anda scale was included in each photograph andplaced parallel to the occlusal plane. Theprints were made at #5 magnification,which proved to be a suitable magnificationfor using a planimeter (Ushikata X-Plan360d). The boundaries of the crown, andthat of each individual cusp (following thecriteria of Wood et al., 1983) were markedwith ink on the photographs. FollowingWood & Abbott (1983), the original mesialand/or distal borders of the teeth with inter-proximal wear were estimated by referenceto the overall crown shape and the buccolin-gual extent of the wear facets. Before obtain-ing any measurement, the exact enlargementof each print was checked using the planim-eter. Tests showed intraobserver measure-ment error to be less than 1%. The overallcrown size (measured crown area: MCA)was taken to be the sum of the areas of thefour or five major cusps).
For comparative purposes we have usedthe MD and BL dimensions of the Homospecimens and samples listed in Table 2.Furthermore, references to these metric datain other hominids included in the genusAustralopithecus and Paranthropus wereobtained from Johanson & White (1979),Johanson et al. (1982), White et al. (1994),and Blumenberg & Lloyd (1983). We havealso used crown and cusp area data pub-lished by Wood et al. (1983), Wood &Uytterschaut (1987), Wood & Engelman(1988), and Bromage et al. (1995).
Apart from the new species representedby the Gran Dolina hominids, we recognizethe following Homo species: H. rudolfensis,H. habilis (s.s), H. ergaster, H. erectus (s.s)(sensu Wood, 1992), H. heidelbergensis (theEuropean Middle Pleistocene hominids), H.neanderthalensis, and H. sapiens. We refer tothe African Middle Pleistocene hominids,such as those of Tighenif, Rabat, SidiAbderrahaman, Thomas I, and Olduvai(OH 22), simply as AFMP, thus avoidingfor the moment the commitment of formally
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List of the Homo specimens and samples whose mesiodistal and buccolingualtooth measurements are used for comparison with the Atapuerca TD6 dentalsample
OH 6, 7, 13, 16, 24 and 39 Tobias (1991)OH 22 Rightmire (1980)UR 501 Bromage et al. (1995)KNM-WT 15000 Brown & Walker (1993)SK 27 Wolpoff (1971)KNM-ER 820, 992 Leakey & Wood (1973)KNM-ER 803, 808, 1590, 1805, 1813 Leakey et al. (1978)KNM-ER 3733 Leakey & Walker (1985)KNM-BK 67 and BK 8518 Wood & Van Noten (1986)Dmanisi Gabunia & Vekua (1995)Sangiran S7 Grine & Franzen (1994)Sangiran 4 and B Wolpoff (1971)Sangiran 17 Jacob (1973)Zhokoudian Wolpoff (1971)Tighenif 1, 2 and 3 AuthorsRabat Thoma & Vallois (1977)Casablanca Howell (1960)Thomas I Sausse (1975)Mauer Howell (1960)Atapuerca-SH AuthorsArago 2, 13, 21, 26, 36, 59 and 60 AuthorsPetralona Authors, in a castMontamaurin (isolated teeth) Billy (1982)Montmaurin (mandible) AuthorsLa Chaise (Suard Cave) Genet Varcin (1975, 1976)Lazaret AuthorsNeandertals from Western andCentral Europe and Near East
This sample includes the specimens listedin Table 6 of Bermudez de Castro (1986),as well as the specimens of Tabun(Lumley, 1973) and Shanidar (Trinkaus,1983)
Table 2
assigning these hominids to a Homo species.The state of some of the dental featuresanalysed in this study was noted for eachone of these species/groups. Furthermore,the state of the dental features was alsonoted for A. afarensis. This species was thusused as a reference group, or outgroup incladistic terms.
In order to characterize the shape of eachspecimen and the samples, we calculated thefollowing indices: the ratio of computedcrown areas of the anterior and posteriorpremolars [(CCA) P3/P4 and (CCA) P3/P4],the first and second molars [(CCA) M1/M2
and (CCA) M1/M2], and the lateral incisorsand first molar [BL I2/(CCA) M1 and BLI2/(CCA) M1].
The first molar was used as the referencebecause this tooth is the most stable of themolar dental field (Dahlberg, 1945). TheCrown Shape Index (CI=BL/MD#100)was also calculated for the lower and upperteeth.
We have compared the tooth shape ofH1 from TD6 with the following specimensand samples: the Atapuerca-SH (H. heidel-bergensis), Neandertal (H. neanderthalensis),Zhoukoudian (H. erectus), and GranCanaria (H. sapiens) samples (which arerepresented by their corresponding meanvalues for each variable), as well as thespecimens OH 7 (H. habilis), KNM-ER992 and KNM-WT 15000 (H. ergaster),Mauer (H. heidelbergensis), Tighenif 3, and
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Dmanisi. In order to analyse the relativeproportions of the dimensions of the TD6teeth in comparison with these specimensand samples these we have processed thedata as follows:
First, we obtain the value of the expres-sion:
TD6 Vi /1/2(TD6 Vi+SiVi) (1)
where Vi (i=1 . . . n) is the value of each ofthe n variables analysed in TD6 and in the Si
(i=1 . . . n) specimens or samples. In orderto include the greatest number of specimensin this analysis, we have used the MD andBL dimensions of the mandibular I2, C, P3,P4, M1, and M2 for the comparison. Theexpression [Equation (1)] represents a sizeratio between TD6 and the comparativesample. If the value of the variable in TD6 isidentical to the value of the variable in oneSi, then the expression [Equation (1)] isequal to 1; if the value of the variable inTD6 is greater than the value of the variablein one Si, then the expression [Equation (1)]is >1, and vice versa.
Then, let us calculate the average of thetwelve values obtained by Equation (1) forthe comparisons between TD6 and each oneof the ten specimens (six) and samples(four):
The expression [Equation (2)] is called the‘‘average dental ratio’’ (ADR). Thus wehave obtained ten ADR values.
If the expression [Equation (2)] is >1, itmeans that the values of the dimensions ofthe TD6 are, on average, greater thanthose of the particular specimen or sampleand vice versa. This may be illustrated bymeans of bivariate scattergrams: the ADRobtained for all comparisons (e.g. in theX-axis) vs. the value of the expression[Equation (1)] (Y-axis) for each variable.
Obviously, the expressions [Equations (1)and (2)] take the value 1 when Si=TD6;that is to say, when we compare TD6 withitself. In this case, the point representingTD6 will be on the line X=Y. Regardingthe comparison between TD6 and theother specimens and samples, the greaterthe difference between the expressions[Equations (1) and (2)] for a certain vari-able Vi, the greater the distance of thespecimen or sample Si to the line X=Y forthis variable.
In the bivariate scattergram obtained forany of the Vi variables, when a specimen orsample is located on the upper part definedby the X=Y line it implies that this speci-men, or sample, shows a proportionalitylesser value than TD6 for the variable atissue and, vice versa, when a specimen, orsample, is placed on the lower part asdefined by the X=Y line, it implies that thisspecimen or sample shows a proportionallyhigher value than TD6 for the variableconsidered.
The variance of the distribution of allTD6 Vi((TD6 Vi+Si Vi)1/2) values repre-sents the so-called WF distance (Ö) betweenTD6 and one of the specimens or samples(e.g. SA). In order to make a global assess-ment of the tooth shape using the informa-tion available from most specimens andsamples, and to assess phenetic affinitiesamong all these specimens and samples, wehave obtained the shape distance, firstdefined in Bermudez de Castro (1993), asfollows:
where i=1 . . . n, and SA Vi and BB Vi are thevalues of the variable Vi in samples, orspecimens, SA and SB respectively, andwhere Ö=0 expresses the identity in shape
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Descriptions
Figure 1. Occlusal view of: (a) ATD6-8, right P4; (b) C and P3 of the maxillary fragment ATD6-13; (c)ATD6-9, left P4; (d) ATD6-7, right P3; (e) ATD6-11, left M1; (f) ATD6-10, right M1; (g) ATD6-12,right M2; (h) ATD6-3, right P3; (i) ATD6-4, right P4. All these teeth belong to Hominid 1 from TD6. (j)dc and dm1 of the maxillary fragment ATD6-14 (Hominid 2). Approximate enlargement 2.85#.
Figure 2. Buccal aspect of the deciduous canine and first molar of the maxillary fragment ATD6-14,belonging to hominid 2 from TD6. Scale bar 1·5 cm.
Upper deciduous canineThe condition of the dc of ATD6-14 isexcellent (Figures 1 and 2). Wear hasblunted the pointed apex of the crown, butno dentine is exposed. Wear also affects thelingual face, flattening the mesial marginalridge and the central ridge. A small mesialinterproximal wear facet is present.
The occlusal outline is a MD-elongatedasymmetrical ovoid. Near the mesial anddistal corners, the occlusal edges exhibit adeep notch, which delimits the main cuspfrom well-differentiated mesial and distalcusplets or styles. In labial view the crownshows a pentagonal shape. The apical halfof the labial face is strongly convex MD.This surface also shows a marked lingual
between SA and SB. From the dissimilaritymatrix formed using this expression, clusteranalyses (UPGMA method) were carriedout. These analyses were performed usingthe NTSYS program (Rohlf, 1992). Inorder to test the goodness of fit of thecluster analyses to the data, the MXCOBLIQUAMP program (Rohlf, 1992) wasused to compare the cophenetic matrix andthe original matrix that was clustered.
Furthermore, in order to assess pheneticsimilarities between the TD6 hominids andother fossils, a principal component analysis(PCA) on 45 specimens (including 25modern human individuals) was also madeusing 12 dental variables: the MD and BL ofI2–M2 (raw data). The Stratgraphics statisti-cal package (1986) was employed to makethis analysis.
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inclination, and is bounded by mesial anddistal depressed areas and grooves, whichemphasize the independence of the mesialand distal styles. The central area of thelabial face is crossed by three short verticalgrooves, whereas the cervical third of thisface exhibits a strong basal prominence.Viewed lingually, the styles are bounded byshort mesial and distal grooves. The broadmesial and distal marginal ridges extendfrom the apex to the strong basal swelling,but no lingual tubercle is present. Thelingual face also shows a broad centralridge, which is delimited by mesial and distallongitudinal grooves. This face is notshovel-shaped.
Upper deciduous first molarThe crown of the dm1 of ATD6-14 is well-preserved (Figures 1 and 2). Occlusal wearhas smoothed the topography of the lingualslopes of the paracone and metacone, as wellas the buccal slope of the protocone. Thereis no evidence of enamel crenulations orsecondary fissures. There are point dentineexposures on the protocone and themesiostyle.
The occlusal outline is a roundedrectangle with a pronounced MB extension,due to the presence of a strong and bulbousmolar tubercle. The protocone is the largestcusp, followed by the paracone and meta-cone. The hypocone is absent. The mesialmarginal ridge is strongly developed, andforms a mesiostyle at the buccal half of theocclusal face. The mesiostyle is separatedfrom the paracone by a long and broad foveaanterior. The crista obliqua is well devel-oped, and not interrupted by the medianlongitudinal groove. The fovea posterior islocated at the intersection of the distal partof the median longitudinal groove and a longBL groove, which represents the boundarybetween the protocone and metacone and awell developed distal marginal ridge. Themedian longitudinal groove also extends onto the distal face. In buccal view, a short
groove, which extends below the occlusalrim, delimits the distal slope of the paraconeand the mesiostyle. The lingual face exhibitssome longitudinal shallow grooves and astrong basal prominence. In distal view, themolar tubercle sticks out as marked basalprominence.
Upper lateral incisorThe crown of the right I2 of ATD6-69 is ingood condition (Figure 3). Incisal wear hasproduced a slightly convexity of the incisaledge, and exposed a very narrow dentinestrip, which is about 3·0 mm long.
The labial face shows a gentle convexityfrom the cervical line to the incisal rim. Inlateral view, the labial face is inclined lin-gually. In lingual view, three clear longitudi-nal grooves are observed. The shallow distalgroove represents the limit between the con-spicuous distal marginal ridge and a welldeveloped central–distal ridge. The distalmarginal ridge begins at the occlusal–distalcorner and expands cervically to form thelingual basal prominence. A central anddeeper groove delimits the central–distalridge and a less prominent central–mesialridge. This groove ends at the basal promi-nence and forms an incipient lingual fovea.The two central ridges end about 2·4 fromthe incisal edge. Finally, a mesial groovedelimits the central–mesial ridge and thewell developed mesial marginal ridge. Anotch breaks the continuity between themesial marginal ridge and the basal promi-nence. The area between the central ridgesand the incisal edge is concave, and thistooth exhibits a characteristic shovel shape.Some gentle cervical-occlusally directedenamel folds complicate the topography ofthe labial surface.
Upper caninesThe left C of H1 and H3 are in goodcondition (Figures 1, 3 and 4). The H3 Cdid not reach the occlusal plane, and thedistance from the labial alveolar border to
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the tip of the crown measures 8·5 mm.Occlusal wear has rounded the crown of theC of the H1 and exposed a small diamond-shaped dentine patch about 2·4 mm long.
The occlusal outline is an ovoid. Viewedlabially, the crown is asymmetrical in boththe angle of the slope and the length of themesial and distal occlusal edges, the distalbeing longer and more inclined than themesial. The upper half of the labial faceshows several grooves and gentle enamelfolds, which run occlusal–cervically and givea ridged aspect to this face. The C of the H1exhibits a mild hypoplastic line, which islocated 4·4 from the buccal cervical line.The lingual face is marked by the mesial anddistal marginal ridges, the mesial one beingmore strongly developed. Both marginalridges flow into the swollen lingual basalprominence. A central longitudinal groovedelimits the broad and shallow mesial-central and distal-central ridges, whichbarely jut out from the flattened lingualsurface.
The root of the H1 C is MD compressed,and exhibits broad mesial and distal longitu-dinal grooves. These grooves differentiatethe labial and lingual components of theroot, the labial being dominant.
Figure 3. Occlusal aspect of the lateral incisor, canine, third and fourth premolars and first molar of themaxilla ATD6-69, belonging (Hominid 3) from TD6. Scale bar 19 mm.
Upper third premolarsThe left and right P3s of H1 and H3 are ingood condition (Figures 1, 3 and 4). Theapices of the buccal and lingual roots of theH1 left P3 are missing. The buccal root ofthis specimen was accidentally broken, but ithas been restored.
The H3 left P3 shows slight occlusal wearon the summit and distal edge of the proto-cone, as well as distinct wear facets on thesummit, mesial and distal edges, and lingualslope of the paracone. In the right P3 of thisindividual, occlusal wear has created facetsonly on the summits of the paracone andprotocone, as well as on the mesial edge ofthe paracone. Furthermore, the left P3
exhibits an incipient interproximal wearfacet on the mesial and distal aspects of the
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Figure 4. (a) Mesial view of the right M2 ATD6-12; (b) buccal aspect of C and P3 of the maxillaryfragment ATD6-13; (c) distal view of the right P3 ATD6-7; (d) mesial view of the left P4 ATD6-9; (e)mesial view of the right P4 ATD6-8; (f) distal view of the left M1 ATD6-11; (g) distal view of the right M1
ATD6-10. Scale bar 1 cm.
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Table 3 Relative cusp areas of postcanine teeth (in %)
*East African Homo, according to Wood et al. (1983); Wood & Uytterschaut (1987), and Wood & Engleman(1988). This hominid sample includes the following specimens: KNM ER 806, 809, 820, 992, 1502, 1507, 1590,1808, and 3734; OH 6, 7, 13, 16, and 24.
†Modern human sample (Frisians) from Dukkum (The Netherlands): Hills et al. (1983).‡Data from Bromage et al. (1995).
paracone. Thus, there is evidence that theleft C and P4, and P4 of the H3 reached theocclusal plane and were functional. Slightocclusal wear has rounded and smoothedthe reliefs of the summits, and the mesialand distal marginal ridges of the H1 P3s. Inthese specimens, clear but not markedmesial and distal interproximal wear facetsare also present.
The occlusal outline of the P3s is a mesio-distally compressed oval, the buccal halfMD broader than the lingual. The maxi-mum MD length is obtained between pointslocated in the confluence of the mesial anddistal slopes of the paracone and the mesial
and distal marginal ridges. The maximumBL breadth is mesial to the midpoint of thelongitudinal axis, since the greater swellingof the buccal and lingual face corresponds tothe mesial aspect of these faces. The area ofthe paracone is clearly greater than the areaof the protocone (Table 3), especially in theH3 P3s. The median longitudinal groove isstraight, but courses irregularly in the H1P3s, whereas this groove is gently convexbuccally in the H3 P3s. The median longi-tudinal groove cuts both the mesial anddistal marginal ridges, and comes down ashort stretch along the mesial face. Thelingual slope of the paracone and the buccal
534 . . ET AL.
slope of the protocone exhibit moderates(H1) or remarkable (H3) enamel crenula-tions and secondary fissuration. The mesialand distal marginal ridges are well devel-oped, especially on the paracone, where theyare delimited by mesial and distal grooves,which connect with the median longitudinalgroove at the level of the fovea anterior andthe deeper fovea posterior.
In lingual view, the summit of the proto-cone is clearly mesially placed, the distaledge of this cusp being longer and lesssloping than the mesial edge. In contrast,the summit of the paracone occupies a cen-tral position. In mesial or distal views, thestrong development of the buccal basalprominence is remarkable, especially on theH3 P3s, producing a characteristic lingualinclination of the labial face. This surface iscomplicated by the presence of severalenamel ridges, bounded by shallowocclusal–cervical grooves. These enamelridges are not a true cingulum. The lingualface is more vertical, and it shows a lessdeveloped basal prominence. A mild hypo-plastic line encircles the H1 P3s about 2·0from the buccal cervical enamel junction.
The root system is single to about 5 mmbelow the cervical enamel junction. Then,the lingual and buccal components separateand course independently about 10 mmalong the distal face. However, the two rootsare joined by a dentine sheet. The mesialface of the buccal root is broader than themesial face of its lingual counterpart, and itis incised by a longitudinal groove.
Upper fourth premolarsThe crown of the right P4 of the H3, andthose of the H1 P4s are well preserved(Figures 1, 3 and 4). The lingual root of theleft UP4 at the H1 is missing. The apicalhalf of the buccal root of the right P4 of thisindividual is also damaged by the loss of alarge slice of the wall, exposing the rootcanal.
The right P4 of the H3 had not reachedthe occlusal plane, and it is not affected byocclusal wear. In the H1 P4s wear has barelyblunted the summit of the protocone, but ithas rounded and faceted the highest zones ofthe paracone. The mesial and distal inter-proximal wear facets of these teeth are suf-ficiently marked to facilitate the fit with theadjacent P3s and M1s.
The occlusal outline of these teeth is arounded rectangle. As in the P3s, the maxi-mum BL breadth is located at the level ofthe buccal cusp. The area of the paracone isgreater than the area of the protocone(Table 3). In the P4 of ATD6-69, the lingualslope of the paracone and the buccal slope ofthe protocone show numerous enamelcrenulations and grooves. The mesial mar-ginal ridge of this specimen takes on theaspect of a cuspule. The occlusal surfaceof the H1 P4s are somewhat less compli-cated, but the enamel folds and grooves arealso striking. In the three P4s the medianlongitudinal groove is gently convexbuccally and has a winding course. Inlingual view, the summit of the protocone isclearly displaced mesially. In the H1 P4sthe summit of the paracone is also clearlydisplaced mesially, but in the right H3 P4,the tip of this cusp occupies a more centralposition. The buccal basal prominence issomewhat less marked than in the P3s, butthe P4s have a noticeable bulbous appear-ance as well. The lingual faces of the P4salso have a well-developed basal promi-nence. Some gentle enamel folds are pre-sented on the buccal face. In the H1 P4s amild hypoplastic line is located 2·8 (right P4)and 3·3 (left P4) from the cervical enameljunction.
The left P4 of the H1 has two independentand well separated buccal and lingual roots.The level of bifurcation occurs about 5·0(distal face) and 7·0 (mesial face) below thecervical enamel junction. In the right P4 ofthe same specimen, the two roots are joinedon the mesial face by a dentine sheet. The
535
buccal root is slightly broader than thelingual.
Upper first molarsIn the left M1 of H1 (Figures 1 and 4) theapical one-third of the BL root and the apexof the buccal component of the MB root aremissing. The L and MB roots have beenrestored, and parts of the root wall are alsomissing. In the right M1 of the H1 most ofthe MB root, and the apical two-thirds ofthe BD root, are missing. The L root ofthis specimen has been restored. In contrast,the crown of the M1s of the H3 are wellpreserved (Figure 3).
Wear on the protocone, hypocone, andthe lingual slopes of the paracone and meta-cone of the H1 M1s has erased all theenamel relief, and exposed minimal dentinecraters. Observation at low magnification ofthese teeth, however, reveals the presence ofvestiges of a complicated topography of theocclusal surface. In the H3 M1s, occlusalwear has facetted the summit of the proto-cone, the mesial marginal ridge, and thelingual slope of the paracone, where it hasproduced a small dentine crater. In thesemolars some enamel crenulations and sec-ondary fissuration are still observed at themesial half of the occlusal surface. The distalhalf is unworn, and numerous enamelcrenulations are intact. In the H1 M1s themesial interproximal facets are well marked,whereas the small distal interproximal facetssuggest that the M2s are recently erupted.
The H1 M1s are occlusally a rounded,slightly BL-elongated, rectangle, whereasthe occlusal outline of the H3 M1s is arounded square. The buccal cusps are setmesial to the lingual ones. In the H1 M1s theprotocone is the largest cusp, followed bythe hypocone, metacone, and paracone,whereas in the H3 M1s the four cusps arefrom largest to smallest protocone, meta-cone, hypocone, and paracone. On themesiolingual surface of the protocone thereis a Carabelli pit. In both H1 and H3 M1s
the crista obliqua is well developed. In theH3 M1s the crista obliqua is almost inter-rupted by the median longitudinal groove.In the H1 M1s the lingual groove extendsbelow the occlusal rim. The buccal faces ofthe paracone and metacone are slightly ver-tically convex, and the mesial and lingualfaces of the protocone, and the lingual anddistal of the hypocone are quite swollen.
In mesial view, the L and BL roots of theH1 M1s bifurcate about 4·0–4·5 from thecervical enamel junction. The L rootdiverges from its buccal counterparts andhardly deviates from the vertical axis of thetooth. This root is BL-compressed, andexhibits a broad and deep longitudinal lin-gual groove, that connects with the lingualgroove of the crown. The MB and DB rootsdiverge each other 4·2 from the cervicalenamel junction. They are BL broad,especially the MB root, and MD com-pressed. The MB and DB roots are incisedrespectively by mesial and distal longitudinalgrooves, that differentiate two components,the most buccal being dominant.
Upper second molarsThe crown of the H1 right M2 is wellpreserved (Figures 1 and 4). However, thefree portion of the DB root and most of theL root are missing. The MB root has beenrestored.
In this specimen, occlusal wear had com-menced and produced small wear facets onthe summit of the protocone, crista obliqua,mesial marginal ridge, and lingual slope ofthe paracone. This tooth also exhibits asmall mesial interproximal wear facet.
The occlusal outline is a slightly BL elon-gated rounded rectangle. The buccal cuspsare mesial to their lingual counterparts.Decreasing cusp size order is protocone,paracone, metacone, and hypocone. Theocclusal surface shows a topography compli-cated by the presence of numerous enamelcrenulations and secondary fissurations.Thus, the crista obliqua is interrupted by
536 . . ET AL.
two grooves, which define a small centralcuspule. The buccal and lingual faces arealso wrinkled by the presence of numerousgentle enamel folds, especially on the lingualface of the protocone. On the mesiolingualsurface of this cusp there is a Carabelli pit.The mesial and lingual faces of the proto-cone, and the lingual and distal faces of thehypocone are quite swollen. A conspicuousbasal prominence emphasizes the buccalface of this tooth. A mild hypoplastic linesurrounding the whole crown is located 3·7from the buccal cervical enamel junction.
The L and MB roots bifurcate about 5·0from the cervical enamel junction. The L rootstrongly diverges from their buccal counter-parts. The MB root is very broad BL and MDcompressed. It has two components, mesialand buccal, with independent radicularcanals. The apex of this root is still open.
Lower central incisorsThe I1 ATD6-52 (Figure 5) has been recon-structed from numerous pieces, and there isloss of small fragments of the crown androot at the level of the joint of the differentpieces. The occlusal distal rim is chipped.Medium incisal wear has exposed a 1·4 widedentine strip. The incisal plane of wearslants lingually. The interproximal wearfacets are well marked, and it is possible tocheck that there is not an adequate fitbetween this tooth and the left I2 ATD6-48,thus excluding the possibility that theybelong to the same individual.
The mesial and distal marginal ridges aremoderately developed, and they merge withthe low lingual basal prominence. The lin-gual basin shows some MD concavity, butthis incisor is not shovel-shaped. In lateralview, the labial face is gently vertically con-vex and strongly inclined lingually. The rootis MD compressed with wide and shallowmesial and distal longitudinal grooves.These grooves differentiate the lingual andlabial components, the latter being slightlybroader than the lingual. In lateral view, the
labial face of the root is gently convex fromcervix to apex. In lingual view, the apicalone-third is inclined towards distal.
Lower lateral incisorsThe I2 of the H1, ATD6-2 (Figure 5), is inexcellent condition, but ATD6-48 preservesonly the crown and a small cervical portionof the distal part of the root (Figure 5). Inthis tooth, two deep fragments havedetached from the crown. One defectextends from the middle of the labial face tothe distolabial cervical corner of the crown.It is 7·5 long, and reaches a maximum widthof 2·0. The other defect extends from theocclusal mesiolabial corner to the cervicalmesiolabial corner of the crown, and is 7·3long and 2·5 wide.
ATD6-2 is moderately worn to expose adentine strip about 0·4 wide. The incisalplane of wear is slightly inclined lingually,and the mesial half of the occlusal surface ismore worn than the distal half. In ATD6-48incisal wear is more advanced with a 0·9–1·3wide dentine strip, and the incisal plane ofwear is slightly inclined lingually. Most wearis at the mesial and distal extremities of theocclusal surface.
In both I2s, the mesial and distal marginalridges are moderately developed, and theyflow into a marked lingual basal promi-nence. The basin between this basal promi-nence and the incisal edge shows some MDconcavity, especially in ATD6-2, so thatthese incisors are moderately shovel-shaped.In lingual view, the mesial and distal edgesof the crown at ATD6-48 exhibit a notice-able divergence from cervical to occlusal.This trait is less conspicuous in the I2s ofH1. Viewed laterally, the labial face isvertically convex and inclined lingually. Theroot of ATD6-2 is MD compressed, andshows broad mesial and distal longitudinalgrooves, the mesial being deeper than thedistal. These grooves clearly differentiatethe lingual and labial components of theroot.
537
Figure 5. (a) Occlusal aspect of the first and second molars of the mandibular fragment ATD6-5. Thethird molar of this specimen did not erupt. (b) Distal view of the right lower C ATD6-1; (c) distal viewof the right P3 ATD6-3; (d) mesial view of the right P4 ATD6-4; (e) lingual view of the left I2 ATD6-48;(f) distal view of the left I1 ATD6-52; (g) distal and lingual aspects of the left I2 ATD6-2. Scale bar 1 cm.
538 . . ET AL.
Lower caninesThe left lower C of the H1 is in goodcondition (Figure 5), except that the rootapex is missing and there is a 7·6#5·5oval-shaped defect on the distal face of theroot near the cervical enamel junction. Asmall fragment of the distal portion of thecrown of the H1 right lower C is also pre-served. In the left lower C, incisal wear hasflattened the summit and mesial and distaledges of the crown, and exposed a 3·3 mmlong diamond-shape dentine strip. Themaximum width of this dentine exposure is0·3.
In lingual view, the crown is oval-shaped.The lingual marginal ridges are well devel-oped, especially the distal one. This ridge isinterrupted by a broad notch, which con-nects with the distal longitudinal groove.The two longitudinal grooves delimit abroad, rounded and gentle median longitu-dinal ridge (lingual ridge). The three lingualridges meets cervically to form the basalprominence. The basin, bounded by theincisal edge, the basal prominence and themarginal ridges, is deep enough to bedescribed as moderately shovel-shaped. Thelabial face is strongly inclined lingually. Alongitudinal groove is present on the distalaspect of the labial face. A small hypoplasticdefect encircles the crown, and is respect-ively 2·5 and 2·2 above the labial and lingualcervical enamel junction.
The left lower C of the H1 has a MD-compressed root. The mesial face is incisedby a broad and deep longitudinal groove,which begins about 5·5 below the cervicalenamel junction and differentiates the labialand lingual components of the root. Thelabial component of the root is broader thanthe lingual. The distal face exhibits only agentle longitudinal depression.
Lower third premolarsThe P3 of the H1 is well preserved, thoughthe apex of the DL root and the apex ofthe mesial component of the MB root are
missing (Figures 1 and 5). Occlusal wear hasflattened the protoconid, especially themesial aspect of this cusp, where a small areaof dentine is exposed. Wear has bluntedthe pointed apex of the metaconid andsmoothed the relief of the mesial and distalmarginal ridges.
This tooth exhibits a strong projection ofthe DL part of the crown, whereas thegreatest development of the buccal basalprominence is slightly mesial in relation tothe midline of the crown. The BL axis isthus perceptibly oblique in relation to theMD axis, and the crown shape is clearlyasymmetrical. Taking into account the pos-ition of the central protoconid ridge, thesummit of the protoconid was probablylocated slightly mesial with regard to themidline of the crown. The tip of the meta-conid is clearly displaced towards mesial inrelation to this midline. Therefore, the sum-mit of the protoconid would be distal to thesummit of the metaconid. The latter is welldifferentiated from the bulk of the meta-conid, and has a bulbous appearance. Thecentral protoconid ridge is not interruptedby the median longitudinal groove. Thisfissure runs in a DL direction, and ends inthe fovea posterior. This fovea is deeperthan the fovea anterior, and is located in thecentre of a large basin bounded by thelingual slope of the protoconid, the distalmarginal ridge, and the buccal slope of themetaconid. All these surfaces show someenamel crenulations. The distal marginalridge is broad and contributes to form aconspicuous talonid.
The shelf-like basal prominence is con-spicuous. The buccal face exhibits a broadand deep MB groove, and a shallow andshort DB groove. The MB groove ends nearthe cervical enamel junction, but the DBgroove barely reaches the basal prominence.All these features form a characteristicU-shaped cingulum. The lingual face alsoexhibits a broad ML groove. A mild hypo-plastic line surrounds the whole crown and,
539
on the buccal face, it is located 3·1 from thecervical enamel junction.
ATD6-3 shows two roots, the DL rootshorter than the plate-like MB root. Thedominant buccal, and the shorter andnarrower mesial components of the MB roothave independent root canals. In mesialview, these components are separated by abroad groove. The roots bifurcate 3·4 fromthe cervical enamel junction, but distally theDL and MB components are joined by adentine sheet, and only the apices are free.
Lower fourth premolarsThe crown of the H1 P4 is well-preserved,but the apical one-third of the DL root andthe apex of the MB root are missing (Figures1 and 5). Moderate wear has smoothed theocclusal surface, and produced facets on theprotoconid, metaconid and the mesial anddistal marginal ridges.
The occlusal outline is a BL-elongated,rounded rectangle, with some extension ofthe DL portion of the crown. The proto-conid summit is mesial with respect to themidline of the occlusal surface, whereas themetaconid summit is mesial to the proto-conid summit. The distal marginal ridge iswell developed and forms the talonid. Thetalonid represents 18% of the total crownarea (Table 3). The buccal face shows astrong basal prominence, which is especiallypronounced on the mesial aspect, oppositethe summit of the protoconid. The MB andDB grooves are somewhat less marked thanin the H1 P3. As they do in the H1 P3, thebuccal grooves and the basal prominenceform a true cingulum. The lingual inclina-tion of the upper half of the buccal face isremarkable. A hypoplastic defect surroundsthe crown and on the buccal face it is located4·4 from the cervical enamel junction.
The H1 P4 has a MB plate-like root and aDL root. The MB root is formed by a mesialand a larger buccal component, with inde-pendent pulp canals. In the distal side, thepreserved portions of the DL and MB roots
are joined by a dentine sheet. In the lingualside, the mesial component of the MB rootand the DL root bifurcate about 6·9 fromthe cervical enamel junction.
Lower first molarsThe crown of the M1 of ATD6-5 is in goodcondition (Figure 5). Premortem traumahas removed an enamel chip from the mesialpart of the mesial marginal ridge. The mesialface of the anterior root is exposed, and itshows a Y-shaped crack separating thelingual and buccal components, that areslightly displaced to each other and withrespect to the crown. The apex of the lingualcomponent of the mesial root is missing.
Wear has erased all enamel relief andexposed areas of dentine on all five cusps.The buccal, lingual, and median longitudi-nal grooves, and the three foveae are stillvisible, though they have been erased bywear at the margins of the occlusal surface.
The occlusal outline is a slightlyMD-elongated, rounded rectangle. The fivecusps, arranged in a Y pattern, are from thelargest to smallest: protoconid, metaconid,entoconid, hypoconid, and hypoconulid(Table 3). The buccal surfaces of the proto-conid and hypoconid are quite bulbous, andthe maximum swelling is located about 2·8from the cervical enamel junction. There areno traces of buccal grooves and enamelfolds. The mesial root is broad and relativelyshort, and its maximum width is 13·4 m.The buccal and lingual components of thisroot are well differentiated by a broaddepressed area, and about 4 mm of theirapical extremes are free.
Lower second molarsThe crown of the M2 of ATD6-5 is wellpreserved (Figure 5). Occlusal wear has pro-duced wide enamel facets on the lingualslopes of the bucal cusps, and on the buccalslope of the lingual cusps. No dentine isexposed, and most enamel crenulations andsecondary fissurations remain visible.
540 . . ET AL.
The crown shape is an MD-elongated,rounded rectangle. There are five majorcusps arranged in a Y pattern and a smallC7. The protoconid is the largest cusp,followed by the hypoconid, metaconid+C7,entoconid, and hypoconulid (Table 3). Thetopography of the occlusal surface is notcomplicated as that of the M2 of the H1.The buccal face is swollen, and the basalprominence reaches its maximum expres-sion about 2·6 from the buccal cervicalenamel junction. A hypoplastic defect islocated 3·7 from the buccal cervical enameljunction. The radiographic image showsthat the apices of the mesial and lingualroots remain open.
Lower third molarsThe M3 of ATD6-5 is not erupted (Figure5). The root reaches a maximum length of2·4 mm at the level of the lingual distal angleof the crown. A part of the occlusal surface isexposed. There are five main cusps, and aC7. The overall occlusal surface exhibitsmarked secondary fissuration and enamelcrenulations.
Table 4 Tooth measurements of the TD6 teeth. MD: mesiodistal; BL: buccolingual; CCA: computedcrown area (MD#BL); MCA: measured crown area; RL: root length
Tooth Side
Maxillary Mandibular
MD BL CCA MCA RL* MD BL CCA MCA RL*
Hominid 1I2 Left 7·0 7·8 54·6 17·8C Left 8·9 11·0 97·9 18·0 8·1 10·0 81·0 18·5P3 Right 8·4 11·7 98·3 75·0 16·9 8·8 10·6 93·3 65·8 14·7P3 Left 8·3 11·5 95·4 74·1 —P4 Right 8·1 11·6 93·9 72·1 14·4 8·2 10·2 83·6 66·1 —P4 Left 8·0 11·7 93·6 73·2 —M1 Right 12·1 13·1 158·5 128·9 16·1 12·2 11·8 143·9 116·6 16·7M1 Left 12·1 12·9 156·1 129·9 15·8M2 Right 12·1 13·7 165·8 133·3 — 13·5 12·0 162·0 125·4 —
Hominid 2dc Left 7·8 6·7 52·3dm1 Left 8·2 10·4 85·3
Hominid 3I2 Right 8·3 8·2 68·1P3 Right 8·8 11·5 101·2 73·0P3 Left 8·8 12·1 106·5 76·9P4 Right — 11·6 — 72·0M1 Right 11·9 12·1 144·0 110·0M1 Left 12·0 12·0 144·0 113·3
Hominid 4I2 Left 7·6 7·7 58·5
Hominid 5I1 Left — 7·6 —
*For upper teeth measurements were taken on the buccal root, except for the M1s, which were taken on thelingual root. For lower teeth measurements were taken on the mesial root.
Absolute dimensions
The MD and BL measurements, computedand measured crown area, and the maxi-mum root length of the TD6 human teethare presented in Table 4. For comparative
541
Table 5 MD and BL dimensions of the maxillary and mandibular lateral incisors and canines in somespecimens and hominid samples
purposes, the MD and BL dimensions ofother hominids specimens and samples arealso presented in Tables 5 and 6.
The anterior dentition is large. Thedimensions of the I2 of the H3 from TD6are larger than those of the earliest Homoand the mean values of the Zhoukoudiansample, and comparable to those ofKNM-WT 15,000, Rabat, and the meanvalues of the Neandertal sample (Table 5).The I2s from TD6 are also large, especiallythe BL measurements, which are compar-able to those of OH 16, KNM-WT 15000,Mauer, and the mean value of the Neander-tal sample. The dimensions of the C of theH1 from TD6 are at the top of the range ofthe genus Homo, and they are comparable insize to those of OH16, KNW-WT 15000,
and Rabat (Table 5). The BL dimension ofthe lower C of the H1 from TD6 is alsolarge, but the MD dimension is small incomparison to that of OH 7, KNM-ER 992,Dmanisi, KNM-WT 15000, Rabat, and themean value of the Zhoukoudian sample.
In contrast to the large size of the anteriordentition, the TD6 hominids belong to apopulation which suffered a significant sizereduction of the postcanine teeth comparedto the early Homo specimens (Table 6).However, the dimensions of the premolarsand molars of the TD6 hominids are com-parable to those of H. ergaster, as well asto those of Middle Pleistocene specimens,such as OH 22, Tighenif 1 and 3, SidiAbderrahman, Rabat, Arago 21, andsome of the Zhoukoudian hominids. The
542 . . ET AL.
dimensions of the M3 of ATD6-6 (taken byradiography) are comparable to those ofthe M1 of this specimen. Therefore, theH1 individual from TD6 shows theM2>M1=M3 size sequence (see additionalcomments below).
Table 6 Comparison of the computed crown areas of the lower premolars and molars of the hominid1 from TD6 with those of some Homo species and the African Middle Pleistocene (AFMP)sample
Table 3 shows the relative cusp areas of themandibular premolars and molars, and ofthe maxillary molars. For comparative pur-poses, we have included data from a modernhuman sample (mandibular molars), andfrom a sample of Plio-Pleistocene hominidsfrom Koobi Fora and Olduvai. This com-parison is certainly very limited, but rela-tively few authors have published measure-ments of cusps areas in hominid fossil teeth(e.g., Bromage et al., 1995).
The data presented in Table 3 suggest thefollowing observations. First, the relativecusp areas of the maxillary molars are verysimilar in TD6 and the East African earlyHomo sample, with strong development ofthe hypocone. The relative entoconid areaof TD6 is similar to that of the modernhuman sample and greater than those of theEAFHOM sample and UR 501 for both theM1 and M2. A reduction of the relativehypoconulid area of the M2 with respect toearly Homo seems to affect both TD6 andmodern humans. Also noteworthy is thereduction of the relative talonid size ofthe TD6 lower premolars with respect to theearly Homo sample and the UR 501 speci-men. In order to assess adequately thechanges in the relative cusp size, all theseobservations deserve to be examined in thefuture using data from enlarged hominidsamples.
543
Crown index
The crown index (CI) of the lower anteriorteeth of the H1 from TD6 is higher thanthose of KNM-ER 992, KNM-WT 15000,Dmanisi, Sangiran S7, the mean of theZhoukoudian sample, and especially thespecimens included in Homo habilis sensustricto (Table 7). The lower lateral incisorand canine of the H1 from TD6 are thusrelatively broader than those of these Asianand African specimens. In contrast, the CIof the I2 of the Hominid 4 from TD6 is lowand similar to those of Dmanisi and themean of the Zhoukoudian sample, butequally higher than those of the specimensincluded in H. habilis s.s. The CI of the I2 ofthe H1 from TD6 is similar to that of theAtapuerca-SH sample, but lower than thoseof Mauer and the Neandertal sample.
As far as the upper dentition is concerned(Table 8), the CI of the anterior teeth fromTD6 is higher than those of the specimensincluded in H. habilis s.s. The CI of theupper canines from TD6 is also higher thanthose of KNM-WT 15000, SK 27, Rabat,and specimens included in Asian H. erectus.However, the CI of the TD6 I2 is similar tothose of these African and Asian hominids.As a whole, the TD6 anterior teeth are asrelatively broad as the anterior teeth of theEuropean Middle Pleistocene hominids.
The CI of the lower premolars of the H1from TD6 is comprised in a range of about110 to 130, in which most Homo specimensare included (Table 7). Some Homo speci-mens, such as KNM-ER 1802, KNM-BK67, KNM-BK 8518, and especially thoseincluded in H. habilis s.s., exhibit relativelynarrow lower premolars. Similarly, theupper premolars of the Olduvai specimensincluded in H. habilis s.s. are relatively nar-row compared with the upper premolars ofother Homo specimens. The upper pre-molars from TD6 show values of the CIsimilar to those of most specimens includedin Table 8.
The CI of the M1 of the Hominid 1 fromTD6 is similar to that of specimens such asthose of Zhoukoudian, Sangiran, Tighenif,Mauer, Arago, or Atapuerca-SH, etc. Thesehominids show an M1 relatively broaderthan those of African specimens included inH. habilis s.s., H. rudolfensis and H. ergaster(Table 7). The CI of the M2 of the H1 fromTD6 is low, but this index seems to be veryvariable in the genus Homo (Table 7). Theupper molars from TD6 are as relativelybroad as those of other African, Asian, andEuropean hominids except, once more,those of the Olduvai site included in H.habilis s.s. (Table 8).
Interdental indices
Table 9 presents the interdental indicesobtained in the H1 and H3 from TD6, aswell as in other specimens and hominidssamples. We are interested in establishing acomparative context between the anteriorand posterior dentitions of the TD6hominids, and devised four interdentalindices. Two of them compare the BLdimension of the upper and lower lateralincisors with the CCA of the respective firstmolars. The value of the BL I2/CCA M1
ratio of the H3 from TD6 (Table 9) issimilar to those of KNM-WT 15000 andRabat, but clearly greater than thoseobtained in the Olduvai specimens,KNM-ER 808, KNM-ER 1813, and SK 27.In the maxilla of these hominids the pos-terior dentition clearly predominates overthe anterior teeth. In contrast, the meanvalue of this ratio for the Atapuerca-SH,Zhoukoudian, and Neandertal samples isgreater than 6·0, thus reflecting the imbal-ance in favour of a predominance of themaxillary anterior tooth size in these homi-nids. The BL I2/CCA M1 ratio offers similarresults. Thus, the value of this ratio for theH1 from TD6, 5·4, is similarly greater thanthose obtained in specimens assigned to H.habilis s.s., but lesser than those obtained in
544 . . ET AL.
Tab
le7
Cro
wn
ind
exof
the
low
erte
eth
inso
me
Hom
osp
ecim
ens
and
sam
ple
s(m
ean
valu
es)
Spe
cim
en/s
ampl
eI 2
CP
3P
4M
1M
2
OH
796
·111
4·8
101·
096
·483
·892
·6O
H13
—93
·895
·810
3·1
89·2
87·0
OH
1610
0·0
—10
5·5
100·
085
·892
·6O
H22
——
94·0
117·
690
·791
·3U
R50
1—
—12
0·6
111·
684
·281
·4K
NM
-ER
806
——
117·
4—
91·9
91·6
KN
M-E
R82
089
·3—
——
88·5
—K
NM
-ER
992
98·6
100·
012
1·7
129·
189
·994
·7K
NM
-ER
1802
——
107·
510
5·3
87·8
85·4
KN
M-W
T15
000
103·
810
7·8
114·
111
2·2
87·4
91·5
KN
M-B
K67
——
—96
·788
·283
·8K
NM
-BK
8518
——
106·
210
6·7
96·0
85·1
Dm
anis
i10
1·5
95·3
108·
912
0·7
97·7
96·7
Tig
heni
f1
——
120·
012
1·4
95·4
100·
0T
ighe
nif
2—
—12
8·7
123·
992
·897
·1T
ighe
nif
311
0·6
132·
011
5·9
124·
496
·896
·8C
asab
lanc
a—
—11
7·9
—92
·183
·9R
abat
107·
111
1·8
111·
110
5·5
91·7
—T
hom
as1
——
—11
6·7
91·4
87·3
San
gira
nB
——
—11
9·5
104·
010
1·5
San
gira
n9
—12
5·7
124·
212
4·7
——
San
gira
nS
710
3·9
116·
211
2·9
—91
·093
·5Z
houk
oudi
an10
1·1
105·
611
4·0
118·
193
·996
·8(n
=7,
S.D
.=3·
1)(n
=8,
S.D
.=5·
8)(n
=13
,S
.D.=
9·8)
(n=
8,S
.D.=
10·8
)(n
=14
,S
.D.=
2·3)
(n=
11,
S.D
.=5·
3)
545
Tab
le7
Con
tin
ued
Spe
cim
en/s
ampl
eI 2
CP
3P
4M
1M
2
TD
6H
111
1·4
123·
412
0·4
120·
893
·588
·9T
D6
H4
101·
3—
——
——
Mau
er12
2·2
118·
411
1·1
122·
796
·594
·5A
TA
-SH
110·
511
1·6
113·
012
1·0
93·6
92·8
(n=
14,
S.D
.=6·
1)(n
=12
,S
.D.=
10·6
)(n
=14
,S
.D.=
3·9)
(n=
17,
S.D
.=10
·1)
(n=
19,
S.D
.=3·
6)(n
=18
,S
.D.=
2·8)
Mon
tmau
rin
——
——
89·1
98·2
Mon
t.C
.G.
10B
3T—
103·
2—
——
—M
ont.
C.G
.2F
3—
98·9
——
——
Mon
t.14
B3S
——
128·
612
5·0
——
La
Cha
ise
36(A
.S.)
——
141·
8—
——
La
Cha
ise
37(A
.S.)
—12
4·2
——
——
Ara
go2
——
——
99·1
91·6
Ara
go13
——
128·
913
2·9
94·2
95·2
Ara
go24
—11
0·0
——
——
Ara
go28
——
—10
9·7
——
Laz
aret
—11
5·7
——
——
Nea
nder
tals
118·
111
4·2
114·
511
8·4
93·5
92·9
(n=
22,
S.D
.=10
·9)
(n=
30,
S.D
.=7·
7)(n
=36
,S
.D.=
8·3)
(n=
40,
S.D
.=11
·4)
(n=
47,
S.D
.=5·
5)(n
=38
,S
.D.=
5·4)
Gra
nC
anar
ia11
0·2
115·
011
4·5
117·
896
·195
·6(n
=73
,S
.D.=
8·2)
(n=
126,
S.D
.=7·
1)(n
=26
4,S
.D.=
7·0)
(n=
297,
S.D
.=7·
1)(n
=50
4,S
.D.=
4·2)
(n=
507,
S.D
.=3·
9)
546 . . ET AL.
Tab
le8
Cro
wn
ind
exof
the
up
per
teet
hin
som
eH
omo
spec
imen
san
dsa
mp
les
(mea
nva
lues
)
Spe
cim
en/s
ampl
eI2
CP
3P
4M
1M
2
Old
uvai
*94
·210
3·5
123·
012
4·9
98·1
108·
3(n
=3)
(n=
3)(n
=4,
S.D
.=4·
0)(n
=4,
S.D
.=2·
9)(n
=9,
S.D
.=4·
7)(n
=3)
KN
M-E
R80
3—
91·4
——
——
KN
M-E
R80
897
·5—
143·
7—
98·5
—K
NM
-ER
1590
—11
0·6
133·
312
9·5
103·
712
0·8
KN
M-E
R18
0598
·212
0·5
161·
0—
104·
710
7·1
KN
M-E
R18
08—
—16
2·3
——
113·
0K
NM
-ER
1813
89·2
102·
413
8·7
125·
510
2·4
111·
5K
NM
-ER
3733
——
137·
914
9·4
——
KN
M-W
T15
000
97·7
106·
313
4·5
138·
810
0·0
101·
6S
K27
102·
696
·313
9·6
—95
·099
·3R
abat
106·
210
5·3
—13
7·5
100·
011
3·0
Zho
ukou
dian
105·
110
7·8
139·
714
6·9
114·
811
7·4
(n=
3)(n
=5,
S.D
.=5·
9)(n
=6,
S.D
.=11
·0)
(n=
11,
S.D
.=8·
6)(n
=7,
S.D
.=6·
5)(n
=8,
S.D
.=9·
0)S
angi
ran
B10
4—
145·
914
4·7
113·
211
1·8
San
gira
n4
——
147·
614
5·2
——
San
gira
n17
——
139·
512
3·2
116·
711
6·8
San
gira
nS
710
0·0
101·
513
4·3
131·
510
7·9
107·
7(n
=1)
(n=
4,S
.D.=
5·4)
(n=
4,S
.D.=
7·0)
(n=
3)(n
=7,
S.D
.=4·
3)(n
=3)
TD
6H
398
·812
3·6
130·
7—
101·
7—
TD
6H
1—
123·
613
9·3
143·
210
8·3
113·
2A
TA
-SH
98·3
113·
313
2·1
137·
610
3·6
123·
7(n
=8,
S.D
.=3·
3)(n
=9,
S.D
.=4·
7)(n
=8,
S.D
.=4·
5)(n
=10
,S
.D.=
6·2)
(n=
14,
S.D
.=6·
1)(n
=16
,S
.D.=
7·4)
Ara
go21
——
——
107·
111
3·6
Ara
go26
——
—13
2·5
——
Ara
go36
——
131·
3—
——
Ara
go59
—12
1·8
——
——
Ara
go60
96·6
——
——
—N
eand
erta
ls10
6·5
114·
313
7·3
138·
710
6·2
116·
0(n
=27
,S
.D.=
8·6)
(n=
34,
S.D
.=8·
5)(n
=28
,S
.D.=
9·6)
(n=
31,
S.D
.=7·
2)(n
=30
,S
.D.=
7·1)
(n=
29,
S.D
.=10
·9)
Gra
nC
anar
ia(M
ales
)98
·010
9·3
131·
913
9·2
111·
612
1·0
(n=
45,
S.D
.=8·
0)(n
=86
,S
.D.=
6·1)
(n=
126,
S.D
.=5·
7)(n
=14
1,S
.D.=
6·9)
(n=
170,
S.D
.=4·
3)(n
=25
5,S
.D.=
7·0)
*Thi
ssa
mpl
ein
clud
esth
efo
llow
ing
spec
imen
s:O
H6,
13,
15,
16,
21,
24,
39,
41,
44an
d45
.
547
the Atapuerca-SH and Neandertal samples.However, in this case the value obtained forthe Zhoukoudian sample, as well as that ofthe Dmanisi mandible are low and similar tothose of the Olduvai hominids. The valuesfor the BL I2/CCA M1 ratio in KNM-WT15000, KNM-ER 992 and Rabat are similarto that of H1 from TD6.
The size ratio between the maxillary andmandibular P3s and P4s also offers valuableinformation concerning the size relation-ships between the anterior and posteriordentitions. The crown size of the P3 issimilar to that of the P4 in the H1 fromTD6, as well as in OH 13, OH 16, OH 39,and some Sangiran specimens, whereas thecrown size of the P4 is clearly greater thanthat of the P3 in OH 24, KNM-ER 1813and Sangiran 17 [(CCA) P3/P4°100]. Incontrast, this ratio is high in KNM-WT15000, Rabat, and the Zhoukoudian andAtapuerca-SH samples, thus indicating thatthe crown size of the P3 is clearly greaterthan that of the P4. Concerning the man-dibular premolars, H1 from TD6 shows theP3>P4 sequence, and the value of the(CCA) P3/P4 ratio in this hominid is highand similar to those of KNM-WT 15000,OH 22, and Tighenif 3, but clearly lowerthan the mean value of the Atapuerca-SHhominids. In this case, the mean value of theZhoukoudian sample is low (<100) andsimilar to those of OH 13, OH 16, Sangiran9, and Tighenif 2.
On the other hand, H1 from TD6 exhibitsthe M2>M1 size relationship, and the valueof the (CCA) M1/M2 ratio of this hominid issimilar to those of Tighenif 1 and 2, Thomas1, and Arago 13. The value of the CCAM1/M2 ratio is much lower (M2±M1) inPlio-Pleistocene hominids, such as UR 501,OH 13, OH 16, KNM-ER 992, andKNM-ER 1802, whereas the mean valuesof this index for the Zhoukoudian andAtapuerca-SH samples indicate that theM1=M2 and M1>M2 size sequences arefrequent in these hominids. The M1>M2
size relationship is observed in Dmanisi andOH 22 as well. Concerning the maxilla, H1from TD6 also exhibits the M2>M1 sizesequence, as in all Lower Pleistocene homi-nids so far examined. A (CCA) M1/M2 ratiohigher than 100 is obtained for the meanvalues of the Atapuerca-SH and Neandertalssamples (Table 9).
Finally, we have obtained the size rela-tionship between the BL dimension of theP4 and M1. The value of the BL P4/M1 ratiois high in H1 and especially high in H3 fromTD6. In the latter individual the value ofthis index is similar to those of OH 24 andKNM-WT 15000, and beyond the top endof the Middle and early Upper Pleistocenehominid samples (e.g. Zhoukoudian,Atapuerca-SH, and Neandertals).
Shape analysis
Table 10 presents the values of the ex-pression TD6 Vi/1/2(TD6 Vi+SiVi) (seeMethods) and the ADR values. This table,and Figures 6–11, are intended to showwhich are the variables that, in relativeterms, differentiate to a greater extent TD6from the other specimens and samples; or,in other words, which are the variables thatcontribute to a greater extent to establish theWF shape distance between TD6 and theother specimens and samples.
The analysis of the BL dimension of the I2
offers clear results (Figure 6). In relation toTD6, most specimens and samples areplaced in two distinct regions of the bivariatemorphological space. On the one hand,the specimens OH 7, KNM-ER 992, andDmanisi, as well as the Zhoukoudian samplecrowd together on the upper part defined bythe X=Y line and are far from the line.These specimens and the Zhoukoudiansample (mean value) show, in relative terms,a BL dimension of the I2 less than that ofthe H1 from TD6. On the other hand,Mauer, as well as the Neandertals andAtapuerca-SH samples, crowd together on
548 . . ET AL.
Tab
le9
Inte
rden
tal
ind
ices
ofth
ep
erm
anen
tu
pp
erte
eth
inso
me
spec
imen
san
dh
omin
idsa
mp
les
(mea
nva
lues
)
Spe
cim
en/
sam
ple
BL
I2/C
CA
M1
BL
I 2/C
CA
M1
(CC
A)
P3/P
4(C
CA
)M
1/M
2(C
CA
)P
3/P
4(C
CA
)M
2/M
2B
LP
4/C
CA
M1
OH
63·
8—
——
——
—O
H7
—4·
0—
—85
·185
·7—
OH
13—
4·0
102·
789
·294
·876
·390
·5O
H16
3·8
—10
3·8
89·1
99·9
76·3
87·6
OH
22—
——
—11
0·6
104·
1—
OH
24—
—90
·0—
——
94·7
OH
395·
2—
104·
187
·3—
—90
·8K
NM
-ER
808
4·5
——
——
——
KN
M-E
R99
2—
5·4
——
107·
981
·8—
KN
M-E
R15
90—
—97
·180
·9—
——
KN
M-E
R18
02—
——
—89
·981
·6—
KN
M-E
R18
133·
8—
87·3
——
—90
·4S
K27
4·1
——
——
——
KN
M-W
T15
000
5·7
5·8
107·
498
·311
4·9
—95
·9R
abat
5·9
5·7
115·
996
·399
·4—
91·6
UR
501
——
——
114·
971
·3—
KN
M-B
K67
——
——
—88
·0—
KN
M-B
K85
18—
——
——
98·0
—T
ighe
nif
1—
——
—10
1·2
91·1
—T
ighe
nif
2—
——
—92
·891
·9—
Tig
heni
f3
—4·
9—
—10
7·3
98·4
—C
asab
lanc
a—
——
——
95·3
—T
hom
as1
——
——
—91
·9—
Zho
ukou
dian
5·9*
5·2
113·
798
·597
·010
2·8
91·6
(n=
3/7)
(n=
4,S
.D.=
0·7)
(n=
5,S
.D.=
13·1
)(n
=5,
S.D
.=6·
2)(n
=6,
S.D
.=7·
4)(n
=7,
S.D
.=7·
0)(n
=5,
S.D
.=1·
3)
549
Tab
le9
Con
tin
ued
Spe
cim
en/
sam
ple
BL
I2/C
CA
M1
BL
I 2/C
CA
M1
(CC
A)
P3/P
4(C
CA
)M
1/M
2(C
CA
)P
3/P
4(C
CA
)M
2/M
2B
LP
4/C
CA
M1
Dm
anis
i—
4·0
——
106·
311
4·8
—S
angi
ran
4—
—10
1·6
——
——
San
gira
n9
——
——
95·3
——
San
gira
n17
——
92·1
101·
8—
——
San
gira
nB
——
102·
580
·2—
94·7
—T
D6
H1
—5·
410
1·9
94·1
111·
688
·890
·7T
D6
H3
5·7
——
——
—95
·9A
rago
2—
——
——
92·4
—A
rago
13—
——
—10
1·5
88·4
—A
rago
21—
——
92·7
——
—P
etra
lona
——
90·9
109·
9—
—91
·6A
TA
-SH
6·2*
6·1
116·
9*10
9·2
120·
310
3·9*
89·8
(n=
8/10
)(n
=4,
S.D
.=0·
3)(n
=8/
10)
(n=
5,S
.D.=
7·0)
(n=
9,S
.D.=
8·7)
(n=
19/1
8)(n
=4,
S.D
.=2·
7)M
auer
—5·
9—
—10
5·6
85·2
—M
ontm
auri
n—
——
——
102·
9—
Nea
nder
tals
6·1
6·2
107·
510
4·7
104·
397
·585
·9(n
=11
,S
.D.=
0·4)
(n=
18,
S.D
.=0·
6)(n
=21
,S
.D.=
11·4
)(n
=20
,S
.D.=
8·7)
(n=
22,
S.D
.=9·
0)(n
=25
,S
.D.=
7·1)
(n=
19,
S.D
.=3·
7)G
ran
Can
aria
5·2*
5·3*
99·6
*11
0·7*
91·2
*10
7·9*
77·8
(n=
45/1
70)
(n=
73/5
04)
(n=
126/
141)
(n=
170/
255)
(n=
264/
297)
(n=
504/
507)
(n=
331,
S.D
.=4·
4)
*The
inde
xis
calc
ulat
edus
ing
the
mea
nva
lues
ofth
eva
riab
les
inth
eco
rres
pond
ing
popu
lati
onsa
mpl
es.
550 . . ET AL.
Table 10 Values of the expression TD6 Vi/((TD6 Vi+SiVi)1/2), Si
ASH=Atapuerca-Sima de los Huesos; NEA=Neandertals; MAU=Mauer; NAR=KNM-WT 15000;ZHO=Zhoukoudian; TG3=Tighenif 3; 992=KNM-ER 992; DMA=Dmanisi; OH 7; CAN=Aboriginals fromGran Canaria, Canary Islands. ADR: Average Dental Ratio (see text).
1.120
1.120
0.9600.940
Average dental ratio
BL
I2
1.040
1.080
1.040
1.060
1.020
0.980
0.960 1.020 1.060 1.080 1.1001.0000.980
NAR
OH7
TD6
992
ZHO
TG3
DMA
MAU
NEA
ASH
CAN
X = Y
1.000
1.100
Figure 6. Bivariate scattergram of the average dental ratio [Equation (2) in the Methods] vs. the values ofEquation (1) for the BL dimension of the lower lateral incisors. See text for further details.
the lower part defined by the X=Y line, thusreflecting that, in relative terms, the BLdimension of the I2 in these EuropeanMiddle Pleistocene hominids is greater thanin the H1 from TD6. The Tighenif 3 and
KNM-WT 15000 specimens are locatedhalfway between these two groups, whereasthe modern human sample are in the X=Yline. From the biological point of view, theseresults mean that, for instance, if the species
551
1.120
1.160
0.9600.940
Average dental ratio
BL
C
1.040
1.100
1.040
1.080
1.020
0.980
0.960 1.020 1.060 1.080 1.1001.0000.980
NAR
OH7 TD6
992ZHO
TG3
DMA
MAU
NEA
ASH
CAN
X = Y
1.000
1.120
1.140
1.060
Figure 7. Bivariate scattergram of the average dental ratio [Equation (2) in the Methods] vs. the values ofEquation (1) for the BL dimension of the lower canines. See text for further details.
1.120
1.180
0.9600.940
Average dental ratio
BL
P3
1.040
1.100
1.040
1.080
1.020
0.980
0.960 1.020 1.060 1.080 1.1001.0000.980
NAROH7
TD6
992
ZHO
TG3
DMA
MAU NEAASH
CAN
X = Y
1.000
1.120
1.140
1.060
1.160
Figure 8. Bivariate scattergram of the average dental ratio [Equation (2) in the Methods] vs. the values ofEquation (1) for the BL dimension of the lower third premolars. See text for further details.
represented by TD6 and the Atapuerca-SHsample are phylogenetically related, then theevolution from H. antecessor to H. heidel-bergensis was characterized by a relativeincrease of the BL dimension of the I2.
Figure 7 shows the results for the analysisof the BL dimension of the lower C. Thecanine of H1 from TD6 is relatively largerthan the other specimens and samples
(except Tighenif 3), which are lined up onthe upper part defined by the X=Y line.Dmanisi is also placed on this part of thebivariate space, but it is considerably furtherfrom the X=Y line.
Figures 8 and 9 present the results of theanalysis of the BL dimension of the P3 andP4 respectively. For the P3, we pay particularattention to the position of OH 7, Mauer
552 . . ET AL.
1.120
1.120
0.940
Average dental ratio
BL
P4
1.040
1.100
1.080
1.040
1.060
1.020
1.000
0.980
0.960
0.960 1.020 1.060 1.080 1.1001.0000.980
NAR
OH7OH7TD6
992
ZHO
TG3
DMA
MAUNEA
ASH
CAN
X = Y
0.940
Figure 9. Bivariate scattergram of the average dental ratio [Equation (2) in the Methods] vs. the values ofEquation (1) for the BL dimension of the lower fourth premolars. See text for further details.
1.120
1.070
0.9500.940
Average dental ratio
BL
M1
1.040
1.050
1.010
1.030
0.990
0.970
0.960 1.020 1.060 1.080 1.1001.0000.980
NAR
OH7OH7
TD6
992
ZHO
TG3
DMA
MAU
NEA
ASH
CAN
X = Y
Figure 10. Bivariate scattergram of the average dental ratio [Equation (2) in the Methods] vs. the valuesof Equation (1) for the BL dimension of the lower first molars. See text for further details.
and the Neandertals, on the upper part andfar from the X=Y line, and the position ofKNM-ER 992, on the lower part and alsofar from the X=Y line. For the P4, onlyKNM-ER 992 is far from the X=Y line.
The analysis of the BL dimension of theM1 gives interesting results (Figure 10). Theplace of the OH 7, and especially KNM-ER992, and KNM-WT 15000 specimens indi-
cates a relatively small BL dimension ofthe M1 in these fossils in comparison withTD6 and other specimens and samples. Incontrast, Dmanisi and the modern humansamples exhibit a relatively large M1 BLdiameter. The Neandertal, Atapuerca-SH, and Zhoukoudian samples, as well asTighenif 3 and Mauer are near the X=Yline. With regard to the M2, no clear trends
553
1.120
1.100
0.9200.940
Average dental ratio
BL
M2
1.040
1.080
1.040
1.060
1.020
0.980
0.960 1.020 1.060 1.080 1.1001.0000.980
NAR
OH7
TD6
992
ZHOTG3
DMAMAU
NEA
ASH
CANX = Y
1.000
0.960
0.940
Figure 11. Bivariate scattergram of the average dental ratio [Equation (2) in the Methods] vs. the valuesof Equation (1) for the BL dimension of the lower second molars. See text for further details.
are observed for the BL dimension in ouranalysis (Figure 11).
The values of the WF shape distance areshown in Table 11. The North Africanspecimen Tighenif 3 is the nearest to TD6,followed by Mauer, the Neandertals andAtapuerca-SH samples and KNM-WT15000. Other specimens and samples,especially Dmanisi and OH 7, are a longdistance from TD6. The short distancebetween WT 15000 and the Atapuerca-SHand Neandertals samples, the short distancebetween Dmanisi and the Zhoukoudian
ASH=Atapuerca-Sima de los Huesos; MAU=Mauer; NEA=Neandertals; TG3=Tighenif 3; NAR=KNM-WT 15000; ZHO=Zhoukoudian; DMA=Dmanisi; 992=KNM-ER 992.
Table 11
sample, and the considerable distancebetween OH 7 and all other specimens andsamples are also remarkable.
The phenogram shown in Figure 12 illus-trates the relationships between the differentspecimens and samples obtained from thecorresponding matrix of dissimilarity. Twomain groups can be distinguished in thisphenogram: a group formed by Europeanand later African hominids, and another oneformed by Zhoukoudian, Dmanisi, and theAfrican specimen KNM-ER 992. In the firstgroup, the Atapuerca-SH hominids join
554 . . ET AL.
0.000.32
ASH
0.24 0.080.16
NEA
NAR
MAU
TG3
TD6
ZHO
DMA
992
OH7
Figure 12. Cluster formed from the WF dissimilarity matrix. Correlation between the cophenetic andoriginal matrices: r=0·84 (Mantel t-test: t=3·73; P=0·99). Abbreviations of the samples as in Table 11.
Table 12 Principal component analysis of themandibular dental variables
% of varianceCumulative variance
Factor 1 Factor 2 Factor 3
76·376·3
7·483·7
3·787·4
I2MD 0·278 "0·294 0·178BL 0·245 "0·377 "0·745
CMD 0·299 "0·253 0·101BL 0·295 "0·310 "0·105
P3MD 0·313 "0·120 0·252BL 0·295 "0·219 0·251
P4MD 0·280 0·329 0·218BL 0·299 0·305 0·071
M1MD 0·288 0·393 "0·151BL 0·257 0·463 "0·418
M2MD 0·302 0·136 0·094BL 0·303 0·226 0·068
closely the Neandertal sample, whereas theH1 from TD6 joins closely the Tighenif 3specimen. Unexpectedly, KNM-WT 15000is included in this group. In the secondgroup, the Zhoukoudian hominids joins theDmanisi mandible, and this subset joins at agreater distance to KNM-ER 992. Finally,OH 7 clusters at a considerable distancecompared to the other specimens andsamples.
The first three components of the PCAaccount for 87·5% of the variance in thedata (Table 12). The first component (PC1)explains a 76·3% of the total variance. It is asize component, with all dental variablesshowing similar and positive loadings. ThePC2 is a shape component, which explainsthe 7·5% of the total variance. This com-ponent separates the specimens and samplesdue to an antagonistic relationship betweenthe anterior (I2, C, and P3) and posterior(P4, M1, and M2) dentitions. In fact, nega-tive loadings are obtained for the dentaldimensions of the anterior teeth vs. positiveloadings for the dental variables of the pos-terior teeth (Table 12). Note that the P3 is
included in the anterior segment of thedental arcade (see discussion). Figure 13shows the scatter diagram for the PC1 vs.
555
10
3
–3–6
PC1
PC
2
4
2
–1
1
–2
–4 2 6 80–2
0
SH
SH
mean SH
SH
DmanisiOH7
ZHO
TG3
TD6
ER992
WT15000
Mauer
Figure 13. Scatter diagram for the first and second principal components of dental variables. (-)Specimens from the modern human sample of Gran Canaria; (+): individuals from the Neandertalsample: Arcy II, Genay, Le Moustier, Ehringsdorf N, Spy II, Krapina D, Krapina E, Krapina H, andKrapina L; TG3: Tighenif 3; ZHO: mean of the Zhoukoudian sample; SH: individuals from theAtapuerca-SH sample: individuals II, XII, and XXII.
PC2 of dental variables. We can checkagain (PC1) that the dental dimensions ofH1 from TD6 are large and comparablewith those of hominids such as KNM-WT15000, ER 992, Tighenif 3, Dmanisi, andthe Zhoukoudian sample. The extremes ofthe size variation in the hominid sampleanalysed are OH 7 and the females of themodern group.
For the PC2, the H1 from TD6 is placedin an intermediate zone of the morphologi-cal space defined by this component, whichdenotes the balanced size relationshipbetween the anterior and posterior teeth ofH1. The position occupied by OH 7,Dmanisi and the Zhoukoudian hominids inthe scatter diagram indicates the predomi-nance of the posterior dentition over theanterior one in these hominids, whereasthe opposite trend defines the position ofthe Atapuerca-SH hominids and mostNeandertals. The position of the two speci-mens included in H. ergaster, KNM-ER 992
and KNM-WT 15000, also suggests somepredominance of the anterior teeth. How-ever, the combination of the size (PC1) andshape (PC2) place the H1 from TD6 closeto these two African specimens.
On the other hand, the present PCA con-firms the results of the WF shape distanceconcerning KNM-WT 15000, whichclusters with the Neandertals and theAtapuerca-SH hominids. However, there isa clear contradiction between both analysesfor the mandible KNM-ER 992. The PC3is also a shape component, which onlyaccounts for 3·7% of the total variance, butmay help to solve this problem. The BL ofthe I2 and M1 have negative and high load-ings on this factor. In contrast, the MD andBL of the P3 and MD of the P4 have positiveand moderate loadings on the PC3. Thedispersion produced by this componentis lower than that of PC2, but oneAtapuerca-SH individual (XXIII) and theKNM-ER 992 mandible are set apart
556 . . ET AL.
10
3
–1.5–6
PC1
PC
3
4
2.5
0
1.5
–1
–4 2 6 80–2
0.5
SH
SHmean SHDmanisi
OH7
ZHO
TG3 TD6
ER992
WT15000
Mauer
2
1
–0.5
Figure 14. Scatter diagram for the first and third principal components of dental variables. (-) Specimensfrom the modern human sample of Gran Canaria; (+): individuals from the Neandertal sample: Arcy II,Genay, Le Moustier, Ehringsdorf N, Spy II, Krapina D, Krapina E, Krapina H, and Krapina L; TG3:Tighenif 3; ZHO: mean of the Zhoukoudian sample; SH: individuals from the Atapuerca-SH sample:individuals II, XII, and XXII.
Summary of the character analysis
Table 13 presents the state of some dentalfeatures observed in A. afarensis and thedifferent Homo species. Several interestingobservations deserve to be emphasized.Firstly, H. antecessor shares with the African
Middle Pleistocene hominids the state of alldental features analysed, except that of traitH (mandibular premolar root morphology).In any case, no specimen of the hominidfossil record shows a morphology of the P3
and P4 roots similar to that of H. antecessor.H. antecessor shares with H. ergaster the
state of 11 traits. Furthermore, the mor-phology of the mandibular premolar roots ofH. antecessor (state 3) shows some simi-larities with states 1 and 2, which areobserved in H. ergaster (see discussion). H.ergaster shows an M1 relatively narrowerthan in H. antecessor (trait N), whereas thelower canine and M3 are relatively smaller inthe latter species than in H. ergaster (traits Cand K). H. antecessor also shares with AsianH. erectus the state of 11 dental traits,whereas both species differ in traits B, C,I, and H. Nevertheless, some of themore recent H. erectus specimens (e.g.,Zhoukoudian) exhibit some ‘‘progressive’’traits with regard to H. antecessor, such as
(Figure 14). The WF distance seems to besensitive to the relative and particularlynarrow I2 and M1 of KNM-ER 992, and itdetermines the proximity of this specimen toOH 7 and the Zhoukoudian sample. Incontrast, the I2 and M1 of KNM-WT 15000are relatively broad, and thus this specimendoes not cluster with KNM-ER 992. In thisrespect, it is important to remember thedifficulties of making assumptions aboutpopulation parameters when dealing withisolated specimens. Finally, the PCA (PC2and PC3) gives results compatible with theclustering of TD6 and Tighenif 3 in thephenogram.
557
T
able
13S
tate
ofso
me
den
tal
feat
ure
sin
the
Hom
osp
ecie
s.*
Fea
ture
A.
afar
ensi
sH
omo
habi
lis(s
.s.)
Hom
oer
gast
erA
sian
H.
erec
tus
AF
MP
Hom
oan
tece
ssor
Hom
ohe
idel
berg
ensi
sH
omo
nean
dert
hale
nsis
Hom
osa
pien
s
A.
Sho
vel-
shap
edup
per
inci
sors
.0:
pres
ence
;1:
abse
nce
00
00
00
00
0an
d1
B.
Rel
ativ
eB
Ldi
men
sion
ofth
em
andi
bula
rin
ciso
rsan
dca
nine
s.0:
broa
d;1:
narr
ow0
10
and
11
00
00
0C
.A
bsol
ute
MD
dim
ensi
onof
the
man
dibu
lar
cani
nes.
0:lo
ng;
1:sh
orte
ned
00
00
11
11
1D
.C
ingu
lum
inm
andi
bula
rca
nine
san
dpr
emol
ars.
0:pr
esen
ce;
1:ab
senc
e0
00
and
10
00
11
1E
.C
row
nsh
ape
ofth
em
andi
bula
rP
3.0:
stro
ngly
asym
met
rica
l;1:
sym
met
rica
lor
mod
erat
ely
asym
met
rica
l0
00
00
01
11
F.
Rel
ativ
eB
Ldi
men
sion
ofth
em
andi
bula
rP
3.0:
broa
d;1:
narr
ow0
10
00
00
00
G.
Tal
onid
ofth
em
andi
bula
rP
3.0:
wel
lde
velo
ped;
1:sm
all
orab
sent
00
00
00
11
1H
.M
andi
bula
rpr
emol
arro
otm
orph
olog
y.†
1:2R
:MB
+D
;2:
2R:M
+D
;3:
2R:M
B+
DL
;4:
2T;
5:1T
;6:
1R1,
2an
d5
1,2,
5an
d6
1,2,
4an
d6
4,5
and
64,
5an
d6
36
66
I.M
andi
bula
rP
3/P
4si
zese
quen
cefo
rth
ecr
own
area
.0:
P4
>P
3;1:
P4
<P
3;2:
P4
=P
30
01
01
11
12
J.M
andi
bula
rM
1/M
2si
zese
quen
cefo
rth
ecr
own
area
.0:
M1
<M
2;1:
M1
>=
M2
00
00
and
10
00
and
10
and
11
K.
Man
dibu
lar
M1/
M3
size
sequ
ence
for
the
crow
nar
ea;
0:M
1<
M3;
1:M
1>
=M
30
00
0an
d1
11
11
1L
.M
axill
ary
M1/
M2
size
sequ
ence
for
the
crow
nar
ea.
0:M
1<
M2;
1:M
1>
M2
00
00
and
1?
00
and
11
1M
.H
ypoc
onul
idin
the
man
dibu
lar
M1
and
M2.
0:pr
esen
tan
dw
ell
deve
lope
d;1:
redu
ced
insi
zean
d/or
inci
dent
ally
abse
nt;
2:fr
eque
ntly
abse
ntin
M2
and
less
soin
M1
00
00
and
10
00
and
11
2N
.R
elat
ive
BL
dim
ensi
onof
the
man
dibu
lar
M1.
0:re
lati
vely
broa
d;1:
rela
tive
lyna
rrow
01
10
00
00
0O
.T
auro
dont
ism
.0:
pres
ence
;1:
hype
r-ta
urod
onti
smor
radi
cula
rta
urod
onti
sm;
2:ab
senc
e0
00
00
01
12
Tho
ugh
som
esp
ecie
sex
hibi
ta
poly
mor
phis
mfo
rse
vera
ltr
aits
,w
hen
one
ofth
est
ates
iscl
earl
ypr
edom
inan
tit
isco
nsid
ered
this
isth
est
ate
pres
ent
inth
esp
ecie
s*T
heta
xon
H.
erga
ster
incl
udes
the
follo
win
gsp
ecim
ens:
KN
ME
R80
6,73
0,82
0,99
2,37
33,
3883
,K
NM
WT
1500
0.A
sian
H.
erec
tus
incl
udes
the
Low
eran
dM
iddl
esp
ecim
ens
from
Tri
nil,
San
gira
n,(P
ucan
gan
and
Kab
uhF
orm
atio
ns)
and
Zho
ukou
dian
.T
heA
FM
Fgr
oup
incl
udes
:O
H22
,K
GA
10-1
,T
ighe
nif
1,2
and
3,T
hom
as1,
Rab
at,
and
Sid
i-A
bder
rahm
an.
†The
prem
olar
root
form
clas
sific
atio
nus
edin
this
tabl
eis
sim
ilar
toth
atof
Woo
det
al.
(198
8).
How
ever
,w
eco
nsid
erhe
reth
eca
tego
ry1T
(sin
gle
Tom
es’
root
),w
hich
thes
eau
thor
sin
clud
ein
the
cate
gory
1R(s
ingl
ero
ot).
The
1Tca
tego
ryin
clud
esth
ose
spec
imen
sw
ith
atle
ast
one
groo
veor
clef
ton
the
mes
iolin
gual
surf
ace,
whi
chdo
esno
tle
adto
bifu
rcat
ion
(or
isre
stri
cted
toth
epe
riap
ical
regi
on).
The
root
ofth
ese
teet
hha
stw
oco
mpo
nent
sw
ith
inde
pend
ent
pulp
cana
ls.T
he1T
cate
gory
isco
nsid
ered
tobe
anin
term
edia
test
age
betw
een
Tom
es’
root
(2T
)an
dth
esi
ngle
root
(1R
).
558 . . ET AL.
the size reduction of M2 relative to M1, andthe trend to the disappearance of the Hld inM1 and M2.
H. antecessor shares the state of ten dentalfeatures with H. heidelbergensis. However,only three of these features are derived andalso shared with the AFMP group. Further-more, most H. heidelbergensis specimens(e.g. Mauer and the Atapuerca-SH hominidsample) appear as ‘progressive’, sharing withH. neanderthalensis the state of 15 dentaltraits analysed.
Finally, H. antecessor shares the state of 11dental features with A. afarensis. In cladisticterms, most of the dental traits in H. ante-cessor (A, B, D, E, F, G, J, L, M, N, and O)are probably plesiomorphic for theAustralopithecus/Homo clade. For the traitsanalysed in this study, H. antecessor differsfrom A. afarensis only in some reductionof both the anterior (MD of the lowercanines) and posterior (CCA of P4 and M3)teeth.
Neandertals. Nevertheless, the Mauer speci-men and the Atapuerca-SH hominids showlower incisors as relatively expanded asthose of the Neandertals, thus suggestingthat the greatest increase of the BL dimen-sions of the lower incisors could have beenan early acquisition in European MiddlePleistocene hominids (Bermudez de Castro,1993). The African Middle Pleistocenehominids may also have increased the BLdimension of the mandibular incisors.
In A. afarensis the mean value for the BLdiameter of the I2 is 7·2 (n=7), whereas inH. habilis s.s. the BL diameter of the I2
ranges from 5·8 (KNM-ER 1813) to 8·0(OH 16). In absolute terms, these values arelower than those observed in other Homospecies. In relative terms (e.g., BL I2/CCAM1), the BL diameter of the I2 in A. afarensisand H. habilis s.s. are also lower than thoseof other Homo species. Therefore, it appearsthat a significant increase of the absoluteand relative BL diameter of this tooth char-acterized all Homo evolutionary lines inAfrica, Asia, and Europe (Wolpoff, 1980).This increase probably began some timebefore 1·5 m.y.a. Broad I2s are observed inhominids such as those of Sangiran, Zhouk-oudian, Arago, ATA-SH, Rabat, KNM-WT15000, KNM-ER 808 and TD6 (H3), aswell as in Neandertals.
On the other hand, the P4>P3 size rela-tionship is present in A. afarensis and H.habilis s.s. It is interesting to note that theMalawi Specimen UR 501, assigned to H.rudolfensis (Bromage et al., 1995), exhibitsthe P3>P4 size sequence. The evolution ofthe genus Homo is characterized by analmost isometric reduction of the lowerpremolars. However, the size reduction ofthe P4 was slightly greater than that of the P3
in the African and European Lower Pleisto-cene populations. This leads finally to theP3>P4 size sequence, which characterizesthe specimens OH 22, ER 992, KNM-WT15000, Tighenif 3, Mauer, Arago 13 andAtapuerca-TD6, as well as the Atapuerca-
Discussion
Before commenting on the evolutionaryplacement of the TD6 hominids, we willbriefly review some relevant metrical andmorphological dental features.
In absolute and relative terms (withregard to the MD diameter and the size ofthe whole dentition), the BL diameter of themandibular incisors of A. afarensis is greaterthan those of OH 7, KNM-ER 992,Dmanisi and the Zhoukoudian sample.However, the small size of the BL diameterof the mandibular incisors in these hominidsrelative to A. afarensis, does not occur in H.ergaster (e.g., KNM-WT 15000). Based onthe limited sample available, we can hypoth-esize that a BL expansion of the mandibularincisors characterized African hominid evo-lution throughout the Lower Pleistocene.The TD6 hominids also reflect this expan-sion which, as Wolpoff (1980) suggested,reached its maximum expression in the
559
SH hominids and the Neandertals. In con-trast, Asian H. erectus apparently preservedthe P4>P3 size relationship.
In his analysis of the Atapuerca-SH lowerpermanent dentition, Bermudez de Castro(1993) suggested that, from the evolutionarypoint of view, the boundary between theanterior and posterior teeth in Homo oughtto be placed between the third and fourthpremolars. The present analysis supportsthis hypothesis. In fact, the second com-ponent of the PCA of the hominid dentalmeasurements shows that the P3s co-varywith the incisors and canines. Likewise, vari-ables of the P4s co-vary with those of theposterior dentition (M1 and M2). Thispattern of covariation suggests that the P3sand P4s belong to different dental regions.This way, the size relationship between bothmandibular premolars would reflect thesize relationship between the anterior andposterior teeth as well, and would helpto clarify the evolutionary situation of aparticular hominid specimen or sample(Bermudez de Castro & Nicolas, 1996).With respect to this feature, the TD6 homi-nids exhibit a balanced position, similar tothose of Tighenif 3, Mauer, and someNeandertals, whereas the postcanine teethclearly predominate over the anterior teethin H. habilis s.s., Zhoukoudian and otherAsian specimens. These hominids alsoshow the P4>P3 sequence. The case of theTighenif hominids is interesting. Withregard to the second component of thePCA, Tighenif 3 is placed between theZhoukoudian sample and H1 from TD6(Figure 13). In Tighenif 3 P3>P4 [(CCA)P3/P4=107·3]. However, in Tighenif 1 andTighenif 2 the values of this index are 101·2and 92·8 respectively. The mean value forthe three specimens is 100·4; that is, P3=P4,a size relationship which accounts for certainpredominance of the posterior teeth over theanterior teeth in the Tighenif sample. Thecase of the KNM-ER 992 mandible is para-doxical, due to the simultaneous presence of
narrow incisors (see below) and the P3>P4
size sequence. In this specimen there is apredominance of the anterior dentition(big canines and third premolars) over theposterior teeth (small first molars). Thisspecimen will be considered in more detaillater.
Regarding the upper premolars, theP3=P4 size relationship characterizes A.afarensis and most specimens included inH. habilis s.s. The specimens OH 24 andKNM-ER 1813, included in the latterspecies, as well as Sangiran 17, present theP4>P3 size sequence. The H1 from TD6shares the P3=P4 size sequence with OH 13,OH 16, OH 39, Sangiran 4, and SangiranB, and differs from the Zhoukoudian,ATA-SH, and Neandertal samples, whichshow the P3>P4 size relationship. It seems,therefore, that the size reduction of the P4
was slightly greater than that of the P3 insome Homo lineages, thus leading finally tothe P3>P4 size sequence. However, informa-tion concerning the size of the upper pre-molars is insufficient for some Homo species,and it is difficult to assess this traitadequately.
As far as the molar series is concerned, itis widely accepted that the M2>M1 relation-ship for the crown area represents the primi-tive condition for the genus Homo. Further,those hominid species (e.g., the Paranthro-pus clade) that were involved in a trendtowards the increase of the posterior toothsize also show the greatest size differencebetween the M1 and M2. Concerning thegenus Homo, the oldest specimens exhibitthe M2>M1 relationship, and the greatestdifference occurs in those mandibles attrib-uted to H. rudolfensis UR 501 and KNM-ER1802, as well as in OH 16. According toLieberman et al. (1996), H. rudolfensis sharesmany derived characters with the australo-pithecines. In this respect, UR 501 andKNM-ER 1802 have postcanine teeth aslarge as those of A. africanus, and theyexhibit the M2°M1 relationship as well. H1
560 . . ET AL.
from TD6 shares the M2>M1 primitive rela-tionship with other Lower Pleistocene Homospecimens. In this period, one remarkableexception, the Dmanisi mandible, breaksthe common rule of the size relationshipbetween M1 and M2. In Zhoukoudian, fiveout of a total of seven individuals, as well asOH 22 (Bed III/IV) also exhibit the M1>M2
relationship. This size sequence is alsocommon in the ATA-SH hominids.
The M2>M1 relationship is the plesio-morphic condition for the genus Homo.The trait is especially marked in KNM-ER1590, which is attributed to H. rudolfensis(Lieberman et al., 1996), and OH 16. Bothspecimens have large postcanine teeth. AllLower Pleistocene hominids, includingTD6, exhibit the primitive condition and, asin the lower molar series, the derivedM1>M2 condition was acquired by all laterhominids during the Middle Pleistocene.
Some morphological traits bear on discus-sions of the phylogenetic and taxonomicstatus of the TD6 hominids. The shovel-shape of the upper incisors could be consid-ered a plesiomorphic trait of the genusHomo, common to all Homo species, includ-ing some H. sapiens populations. On theother hand, a well developed shelf-likecingulum seems to be also a plesiomorphictrait of the genus Homo. This trait character-izes most Lower Pleistocene Homo speci-mens (the KNM-ER 992 mandible is aremarkable exception), as well as the MiddlePleistocene hominids assigned to H. erectus(e.g., Zhoukoudian). In contrast, a shelf-likecingulum is absent in H. sapiens, H. heidel-bergensis and H. neanderthalensis. Further-more, the strong asymmetry of the crown ofthe P3 in occlusal view seems to be anotherplesiomorphy of the genus Homo. H1 fromTD6 shares this trait with H. habilis s.s., H.ergaster and H. erectus. A more symmetricalcrown is observed in the P3 of H. sapiens, H.heidelbergensis and H. neanderthalensis. In thetwo latter species, the P3s show a very simi-lar morphology, with a small, inflated, and
centrally positioned lingual cusp (Bermudezde Castro, 1988), and they lack a well-developed talonid. This feature, relativelyfrequent in some H. sapiens populations(e.g., Kaul & Prakash, 1981), could be con-sidered a plesiomorphic trait of the genusHomo as well. H1 from TD6 shares thistrait with the African Lower Pleistocenehominids and H. erectus. Concerning themandibular molars, the M1 and M2 of H1from TD6 have a well differentiatedhypoconulid. As is well known, the presenceof the main five cusps separated by aY-groove pattern is also considered to be aplesiomorphy of the genus Homo. The sup-pression of the hypoconulid may occur inci-dentally in the M1 of the Middle Pleistocenepopulations (e.g., Atapuerca-SH), but four-cusped M2s are frequent in these popu-lations (Montmaurin, Arago 6, Pontnewydd2, Atapuerca-SH: nearly 60% of the speci-mens), as well as in late Asian H. erectus (e.g.Zhoukoudian). The presence and degree ofthe enamel crenulations (another presumedplesiomorphy of the genus Homo) is variablein different hominid groups, whereas thealmost total disappearance of this trait is amodern feature. The absolute and relativesize of the pulp chamber ought to be ana-lysed in large hominid samples in order toassess this feature adequately. It seems,however, that a wide pulp chamber (tauro-dontism) is the primitive condition of thegenus Homo (Zilberman & Smith, 1992),whereas the apical extension of the pulpchamber due to a delay in fusion of theinterradicular processes (radicular tauro-dontism) would be a derived trait commonto H. heidelbergensis and H. neanderthalensis.Finally, the presence of a strong molartubercle and a small parastyle on the upperdm1 may be a plesiomorphic trait of theTD6 hominids as well.
The morphology of the H1 P3 and P4
roots deserves mention, since it representsa novelty in the hominid fossil record(Table 14). This morphology probably
561
Premolar root form in hominids
1R 1T 2T 2R: MB+DL 2R: MB+D 2R: M+D
A. afarensis1 P3 * *P4 +
A. africanus1 P3 * *P4 +
P. robustus1 P3 * *P4 + +
P. boisei1 P3 * *P4 +
H. rudolfensis2 P3 * * *P4 +
H. habilis s.s.3 P3 * * *P4 + + +
H. ergaster4 P3 * * *P4 + +
K.F. Homo5 P3 * * *P4 + +
AFMP6 P3 * *P4 + + (+) +
TD6 H1 P3 *P4 +
H. heidelberg.7 P3 * *P4 +
H. erectus8 P3 * * *P4 + +
Data from: 1. Bromage et al. (1995) and Wood et al. (1988); 2. Bromage et al.(1995); 3. Wood et al. (1988) and personal observations of the authors in casts; 4.Wood et al. (1988) and Brown & Walker (1993); 5. This sample includes the followingspecimens: KNM-ER 819, 1811, 1812, 3889, and 3954 from the Koobi Fora region,which, according to Wood et al. (1988), exhibit taxonomic affinities with the genusHomo. 6. African Middle Pleistocene hominids: Tighenif, Thomas 1, Rabat, and SidiAbderrahaman; data from Arambourg (1963), Sausse (1975), Thoma & Vallois(1977), and Howell (1960); 7. Personal observations of the authors; 8. Data fromWeidenreich (1937) and Jacob (1973).
Table 14
derives from the presumed primitive con-dition 2R: M+D of the ape/hominid clade(Wood et al., 1988). In this plesiomorphiccondition, the buccal component of themesial root is more developed than thelingual component. In contrast, the lingualcomponent of the distal root is domi-nant (Figure 15). Both components of themesial and distal roots have indepen-dent root canals. This primitive conditioncharacterizes some early Pleistocene EastAfrican specimens from the Koobi Foraregion, as well as the KNM-BK 8518Middle Pleistocene specimen from Baringo(Wood & Van Noten, 1986). The most
simple ontogenetic change to explain thetransition from this primitive morphology tothe form observed in the TD6 hominidswould be the suppression of the DB inter-radicular process. This change would lead tothe fusion of the buccal components of boththe mesial and distal roots (Figure 14). Theresultant morphology would be character-ized by a DL single root, which supports awell developed DL part of the crown (talo-nid), and a MB root, with a largely domi-nant buccal component, and a reducedmesial component. In the TD6 lowerpremolars the cervical one-third of theroots are totally fused, and it is possible to
562 . . ET AL.
Figure 15. Hypothetical transformation sequence from the primitive mandibular root form 2R: M+D (A)to the TD6 derived premolar root form (C).
hypothesize a transition from this mor-phology to the more derived condition of asingle root, by the total suppression of theML interradicular process and fusion of thepulp canals.
In sum, the TD6 hominids show somepresumed plesiomorphic dental traits ofthe genus Homo, such as shovel-shapedincisors, presence of shelf-like cingulum, astrongly asymmetrical crown of the P3 witha well developed talonid, complex rootmorphology of the P3 and P4, M1<M2 sizesequence for the upper and lower molarseries, enamel with moderate to markedlycrenulated postcanine teeth, and M1 and M2
with the five cusps arranged in a Y-pattern.Furthermore, the TD6 hominids show arelative increase of the BL dimensions of themandibular premolars and molars comparedwith early H. habilis s.s., and a P3>P4 sizesequence. The simultaneous presence ofthese dental traits suggests an evolutionarystatus for the TD6 hominids similar to thosetraditionally included in the ‘‘Homo erectusgrade’’. Nevertheless, the TD6 hominidsshow some craniofacial traits, which indicatethat there was a clear divergence between
these hominids and H. erectus (Bermudez deCastro et al., 1997). This suggests that thehominids belong to lineages with differentevolutionary trends, that perhaps reflect dis-persion of the genus Homo into Eurasiaduring the Lower Pleistocene. Severalaspects of morphology reflect these trendsand, in accordance with other authors(Tattersall, 1992; Stringer, 1996), webelieve that a fundamental taxonomicrevision is justified in order to reflectthe variability observed in the currentPleistocene hominid fossil record.
Thus, we have proposed recently(Bermudez de Castro et al., 1997) that theAtapuerca-TD6 hominids belong to a newHomo species, H. antecessor, that probablyoriginated in Africa from H. ergaster. Withregard to this latter species, as well as H.habilis s.s., the TD6 human remains belongto a group of hominids characterized,among other traits, by (1) a size reduction ofthe third molars, (2) a reduction of the MDdimension of the mandibular canine, (3) anincrease of the BL dimension of the man-dibular incisors, and (4) an increase of theBL dimension of the first molars. Other
563
hominids referred to this group include theTighenif hominids (traits 1, 2, 3, and 4).Konso Gardula (at least traits 1 and 4), andOH 22 (at least traits 2 and 4). That is,certain African hominids ranging fromabout 1·4 m.y.a. (Konso Gradula: Asfawet al., 1992) to 0·6 m.y.a. (OH 22:Rightmire, 1980). The P3>P4 size sequencealso characterizes H1 from TD6, Tighenif 3,OH 22, KNM-BK 8518, but also the H.ergaster specimens KNM-ER 992 andKNM-WT 15000.
These features bear witness to the twofundamental trends detected by our uni-variate and multivariate analyses. On theone hand, the size reduction of the posteriorteeth, which follows a determined and uni-versal pattern for all Lower and MiddlePleistocene Homo populatons (see a recentrevision of this topic in Bermudez de Castro& Nicolas, 1995). This is a complex trendfor there is a relative increase in the BLdimension of the M1s, yet an MD reductionof the same tooth. The fossil record islimited, but there do not appear to besignificant differences between the African,Asian and European hominids in the rates ofsize reduction of the posterior teeth duringthe Lower and Middle Pleistocene (but seeBermudez de Castro & Nicolas, 1995). Onthe other hand, a trend towards the sizeincrease of the mandibular anterior teeth,apparently does not characterize AsianH. erectus.
The balance reached by different homin-ids for the two trends represents a usefulmethod to generate hypotheses about thephylogenetic relationships between them.H1 from TD6, and the specimensKNM-WT 15,000, Tighenif 3 and Mauerare at similar stages with respect to the twotrends. Thus, the most reasonable hypoth-esis to interpret the TD6 hominids is thatthey occupied a situation halfway betweenthe more recent populations of H. ergasterand the more ancient populations of H.heidelbergensis seems to be the most reason-
able hypothesis. Along these lines, the Aragohominids deserve a special mention. Inaddition to large size, the Arago dentalremains preserve primitive traits such as thestrong enamel crenulation of the molarocclusal surfaces, a vestige of buccal cingu-lum in some lower premolars, and a certainasymmetry of the crown of the P3s (personalobservations of the authors). In contrast, theDmanisi mandible and the Zhoukoudianhominids are unlike the Gran Dolina homi-nids. On the other hand, the morphologicalanalysis supports a stronger relationshipbetween the TD6 hominids and the AfricanLower and Middle Pleistocene hominidsthan between those and the EuropeanMiddle Pleistocene populations.
To summarize, the TD6 hominids exhibita trend towards the expansion of the man-dibular anterior teeth, inherited from theirAfrican ancestors, together with a moderatesize reduction of the posterior teeth, whileretaining the primitive morphology for mostdental traits. This combination of featuressupports a different taxonomic status forthese hominids than the one used for theEuropean Middle Pleistocene hominids(Bermudez de Castro et al., 1997). Theanatomical dental evidence supporting anancestor–descendant hypothesis for theTD6 hominids and the European MiddlePleistocene hominids is limited. The crownmorphology of the mandibular canine, aswell as the common trend towards theexpansion of the mandibular anterior teethare, for the moment, the only argumentsthat our analyses have revealed in favour ofthat hypothesis (but see Rosas & Bermudezde Castro, 1998). A detailed study of theArago teeth may add to a better understand-ing of this view.
Concluding remarks
This study of the TD6 human remains hasshown that most of their dental traits areprimitive for the Homo clade. From the
564 . . ET AL.
Acknowledgements
We wish to thank Drs Henry and MarieAntoinette de Lumley (Institut de Paleon-tologie Humaine, Paris), Jean-Louis Heim(Musee de l’Homme, Paris), P. Tacquetand Monette Veran (Museum Nationald’Histoire Naturelle, Paris), and Mme
Maryse Tavoso (Laboratoire d’Anthro-pologie, Universite d’Aix-Marseille) forallowing us access to the fossils in their careand providing their kindly help. We alsothank all the people who participate in theexcavation of the Gran Dolina site. Thehuman fossils from TD6 are being restoredby P. Gutierrez and B. Gomez of theMNCN. Help in the field from the GrupoEspeleologico Edelweiss of Burgos ismuch appreciated. We are also grateful toDr Donald Johanson, Dr Bernard Wood,Dr Leslie Aiello, and one anonymous refereefor their valuable comments on the manu-script. This research was supported by theDireccion General de Ensenanza Superiorof the Spanish M.E.C., Project No. PB96-1026-C03-02, and the ‘‘Unidades Asocia-das’’ Program from the CSIC. Funding forthe field work came from the Consejerıa deCultura y Bienestar Social of the Juntade Castilla y Leon. The third author issupported by a CSIC/CAM/MNCN pre-doctoral fellowship.
cladistic point of view, these traits are oflimited use for phylogenetic purposes withinthat clade. In contrast, from the pheneticpoint of view, these traits align TD6 with H.ergaster, H. erectus and some African Lowerand Middle Pleistocene specimens, such asOH 22, Tighenif, and Konso Gardula.Regarding derived traits, the TD6 hominidsshare with H. erectus only size reduction ofthe third molars, a trend common to allhominid lineages. In contrast, H. erectusexhibits narrow lower incisors, which couldbe considered a derived trait shared withsome early H. ergaster, such as KNM-ER992, but not with H. antecessor. The factthat specimens, such as KNM-WT 15000show some expansion of the buccolingualdiameter of the lower incisors, as well asthe P3>P4 size sequence, supports a phylo-genetic relationship between H. ergaster andH. antecessor.
As far as the European hominids are con-cerned, dental traits distance TD6 from H.heidelbergensis, such as Mauer and the SHsample. These latter hominids show at leastnine derived dental traits not shared with theTD6 hominids. Nevertheless, the fact thatH. antecessor shares with H. heidelbergensissome expansion of the mandibular anteriorteeth, some size reduction of the mandibularcanines and third molars, as well as theP3>P4 size sequence, supports a phylo-genetic relationship between the species.Furthermore, the presence in the Aragodental remains of a certain ‘‘primitive dentalpattern’’ deserves to be considered in futurecomparative studies to advance knowledgeof European Pleistocene human evolution.
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