GEOLOGY OF THE DESEADAN (EARLY OLIGOCENE) AGE ESTRATOS S JLLA IN THE SALLA-LURIBAY BASIN, BOLIVIA, WITH DESCRIPTION OF NEW MARSUPIALIA by CARLOS V I L L A R R O E L " 6 LARRY G. MARSHALL "" ABSTRACT R~SUM~ A diverse vertebrate fauna including represen- tatives of at least 22 families of land mammals is known from 500 + m thick Estratos Salla o~ Deseadan (early Oligocene) age in the Salla- Luribay Basin, about 90 km SW of La Paz, Bolivia. Eight principal fossil levels are identified west of Salla concentrated within a 160 m section. A preliminary report on the geology of the Estra- tos Salla is ~jiven, with maps and stratigraphic sections of the fossiliferous levels and localities. Four specimens of fossil marsupials from the Salla~ Luribay Basin in the GEOBOL collection in La Paz are described. Part of a mandibular ramus with two molars represents a new borhyaenid (Sallacyon ho[[stetteri gen. et sp. nov.) ; a relati- vely complete mandible with teeth is refered to the borhyaenid Notogale mitis (AMEGHINO, 1897) ; an associated upper and lower dentition is referred to the palaeothentine (Caenolestidae) Pa/aeo- thentes boliviensis PATTERSON ~ MARSHALL, 1978 ; and a maxillary fragment with poorly preserved M TM apparently represents an enormous palaeo- thentine. La formation de r Estratos Salla >>, d'une 4pais- seur de plus de 500 m, d'age D4s4adien (Oligoc~ne inf4rieur) situ4e dans le bassin de Salla-Luribay 90 km au Sud-Ouest de La Paz en Bolivie, a livr4 une faune de vert4br~s diversifi4e qui inclut des membres d'au moins 22 familles de mammif/~res terrestres. Huit niveaux fossilif4res principaux, compris dans une section de 160 m, ont 4t4 identi- fies h l'Ouest de Salla. On donne une description pr41iminaire de la g4ologie de 1'<~ Estratos Salla >> avec la situation g4ographique et stratigraphique des niveaux et 9isements fossilif4res. On d4crit quatre diff4rents marsupiaux fossiles du bassin de Salla-Lur/bay appartenant a la collection GEO- BOL de La Paz. Un nouveau Borhyaenid4 (Sal- lacyon ho[[stetteri 9en. et sp. nov.) est d4crit /l partir d'une branche horizontale de mandibule avec deux molaires; une mandibule /l peu pr4s compl4te avec ses dents est rapport4e au Borhyae- nid4 Notogale mitis (AMEGHINO, 1897) ; un Palaeo- thentin4 (Caenolestidae) : Palaeothentes boliviensis PATTERSON 0 MARSHALL, 1978, est reconnu ~ partir des dentitions sup4rieure et inf4rieure associ4es; un fragment de maxillaire avec M 1"4 real conser- v4es repr4sente apparemment un 4norme Palaeo- thentin4. KEY-WORDS: SALLA-LURIBAY, BOLIVIA, DESEADAN, OLIGOCENE. MARSUPIAI.IA, DENTITION. MOTS-C1.ES : SALLA-LURIBAY0 BOLIVIE, DESI~AD1EN, OLIGOCENE, MARSUPIAUX, DENTITION. * Divisi6n de Paleontologia, Servicio Geologico de Bolivia (GEOBOL), Casilla 2729 La Paz, Bolivia. ** Department of Geosciences. The University of Arizona, Tucson, Arizona 85721. Geobios, m4moire sp4cial 6 p. 201-211, 8 fig., 2 tabl. Lyon. 1982
Transcript
GEOLOGY OF THE DESEADAN (EARLY OLIGOCENE)
AGE ESTRATOS S JLLA IN THE SALLA-LURIBAY BASIN,
BOLIVIA, WITH DESCRIPTION OF NEW MARSUPIALIA
by CARLOS V I L L A R R O E L " 6 LARRY G. M A R S H A L L ""
ABSTRACT R~SUM~
A diverse vertebrate fauna including represen- tatives of at least 22 families of land mammals is known from 500 + m thick Estratos Salla o~ Deseadan (early Oligocene) age in the Salla- Luribay Basin, about 90 km S W of La Paz, Bolivia. Eight principal fossil levels are identified west of Salla concentrated within a 160 m section. A preliminary report on the geology of the Estra- tos Salla is ~jiven, with maps and stratigraphic sections of the fossiliferous levels and localities. Four specimens of fossil marsupials from the Salla~ Luribay Basin in the G E O B O L collection in La Paz are described. Par t of a mandibular ramus with two molars represents a new borhyaenid (Sallacyon ho[[stetteri gen. et sp. nov.) ; a relati- vely complete mandible with teeth is refered to the borhyaenid Notogale mitis (AMEGHINO, 1897) ; an associated upper and lower dentition is referred to the palaeothentine (Caenolestidae) Pa/aeo- thentes boliviensis PATTERSON ~ MARSHALL, 1978 ; and a maxillary fragment with poorly preserved M TM apparent ly represents an enormous palaeo- thentine.
La formation de r Estratos Salla >>, d 'une 4pais- seur de plus de 500 m, d'age D4s4adien (Oligoc~ne inf4rieur) situ4e dans le bassin de Salla-Luribay
90 km au Sud-Ouest de La Paz en Bolivie, a livr4 une faune de vert4br~s diversifi4e qui inclut des membres d'au moins 22 familles de mammif/~res terrestres. Huit niveaux fossilif4res principaux, compris dans une section de 160 m, ont 4t4 identi- fies h l 'Ouest de Salla. On donne une description pr41iminaire de la g4ologie de 1'<~ Estratos Salla >> avec la situation g4ographique et stratigraphique des niveaux et 9isements fossilif4res. On d4crit quatre diff4rents marsupiaux fossiles du bassin de Salla-Lur/bay appartenant a la collection G E O - BOL de La Paz. Un nouveau Borhyaenid4 (Sal- lacyon ho[[stetteri 9en. et sp. nov.) est d4crit /l partir d 'une branche horizontale de mandibule avec deux molaires; une mandibule /l peu pr4s compl4te avec ses dents est rapport4e au Borhyae- nid4 Notogale mitis (AMEGHINO, 1897) ; un Palaeo- thentin4 (Caenolestidae) : Palaeothentes boliviensis PATTERSON 0 MARSHALL, 1978, est reconnu ~ partir des dentitions sup4rieure et inf4rieure associ4es; un fragment de maxillaire avec M 1"4 real conser- v4es repr4sente apparemment un 4norme Palaeo- thentin4.
* Divisi6n de Paleontologia, Servicio Geologico de Bolivia (GEOBOL), Casilla 2729 La Paz, Bolivia. ** Department of Geosciences. The University of Arizona, Tucson, Arizona 85721.
Fig. 1. - - Map of westcentral Bolivia showing location of Salla-Luribay basin.
Carte du Centre-Ouest de la Bolivle indlquant la situation du bassin de Salla-Luribay.
Diverse vertebrate faunas of Deseadan (early Oligocene) age have been collected by Bolivian, French, and North American paleontologists from the Salla-Luribay Basin, about 90 km southwest of La Paz, Bolivia (fig. 1). T h e fauna includes 8 orders and at least 22 families of land mammals, among which is the oldest known South American primate, Branisella boliviana (Hoffstetter, 1968, 1969, 1976; Hoffs te t te r 6 Lavocat, 1970; Hof- fstetter et al., 1971 ; Hartenberger , 1975 : Lavocat, 1976; Patterson ~ Marshall , 1978; Pat terson W o o d , 1982).
Th e main fossil bearing unit is the Estratos Salla (Evernden et al., 1966; Hoffstet ter , 1976) which attains a thickness of more than 500 m. klnfortu- nately, most of the fossils from the basin simply bear the general label << Salla-Luribay >> with no further information regarding the levels and loca- tions from which they were collected. These fossils are thus of no use in biostratigraphic studies of this extensive sedimentary sequence.
In recent years one of us (C.V.) has conducted a survey of the basin, recording the lithology and strat igraphy of the Estratos Salla, and the strati- graphic occurrence of primary fossiliferous levels and localities. A preliminary report of this study is given here, in hopes that these data will serve as a foundation for more detailed studies in the future.
GEOLOGY OF SALLA-LURIBAY BASIN
The Salla-Luribay Basin is oriented in a N N W - S S E direction, with the Altiplano to the S W and the Cordillera Andina to the N W (figs. 2, 3). It
is filled by two sedimentary units of Tertiary age : 1} the Conglomerado Luribay, a basal psephitic unit; and 2) the overlying Estratos Salla, a pre-
Fig. 2. - - Map of Salla-Luribay Basin showing positions of primary fossil vertebrate localities (based on maps 60~2-I ~ II, Instituto Geogrfifico Militar, Bolivia). Localities are : F-l, Jaroyfilla ; F-2, Aramani Pata ; F-3, Khara Tranca Pata ~ Poco Poconi; F-4, Calabozo Pata; F-5, Tapial Pampa: F-6, Khollpa Jahuira ~ Huaykhallami; FW, Cebadat Churu; F-8, Kollu Huichinca; F--9, Toloma. [According to local natives, Cerro Poco Poconi corresponds to point F-3, and not to the position as indicated on the Instituto Geogr~ifico Militar map, scale 1 : 50,000].
Les principaux gisements de vert6br6s fossiles du bassin de Salla-Luribay (dessind & partir des cartes 6042-I II, Instituto Geogrfifico Militar, Bolivie). Les gisements sont: F=I, ]aroyfilla; F-2, Aramani Pata; F-3, Khara Tranca Pata ~ Poco Poeoni; F-4, Calabozo Pata; F-5, Tapial Pampa; F-6, Khollpa Jahuira 8 Huaykhallami; F-7, Cebadal Churu; F-8, Kollu Huichinca; F-9, Toloma. (D'apr~s les habitants de la r6gion, Cerro Poco Poconi est situ6 au point F-3 et non & la position indiqude sur la carte de l'Instituto Geogrgffico Militar, 6chelle : 1/50000).
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dominantly argillaceous unit with occasional eva- porite and tuffaceous intercalations (Hoffstetter. 1976).
The Conglomerado Luriba 9 is apparently a piedmont deposit formed during the first phases of Andean orogeny. Exposures are limited and appear only in what is interpreted as the lowest level of the basin as seen in the valley of the Rio Mullakha ]ahuira, where at Cancansire it forms vertical walls some 150 m in height. The conglo- merate is composed of clastic elements varying in diameter from a few millimeters to 50 cm with an average of 10 cm. These clasts are composed of white, pink and violet quartzite, with occasional greenish sands. Typically they are subrounded,
but are occasionally subangular. The conglome- rate is intercalated by lenses of dark red, fine to medium grain sands which demonstrate that the Conglomerado dips gently to the NE.
Unconformably overlying the Conglomerado Luribay are 500+ m of the Estratos SaUa, com- posed primarily of consolidated red to pink sandy clays. As a consequence of compressive forces generated during late phases of Andean orogeny, these beds are gently folded and in places form prominent synclines and anticlines. They are eroded into badlands cut by steep walled quebra- das (arroyos). The oldest levels of the Estratos are visible along the Rio Mullakha ]ahuira, beco- ming younger toward ]aruma in the SE. In places
~-#r~'~'~" Ca[abozo Pata I z80 m ~ Pc.-.,) P,:con, i
I " T , , , , , , , , , , , , ,,',:amatfi Pdt.:
T • r.~
i $ . . . . . . . ~ 1 i .J;il;,,/l,,'a
ISig 3. - - Schematic profile of Salla-Luribay Basin showing stratiQraphic positions of pr imary fossil vertebrate localities. Po t orientat ion of profile see fill. 2.
Profil sch~matique du bassin de Salla-Luribay montrant la posit ion strat igraphique des principaux gisements de vert~bres. L'orientat ion de la coupe est indiqu~e sur la fig. 2.
thin intercalations of limestones, marls, conglome- rates, and gypsum occur. The gypsum may be present as thin laminated lenses in the dark red, sandy clays, easily recognizable by their white to light yellow-gray colors. Some of these beds can be used as reliable guide horizons for recording fossil levels and localities. In particular, a 2.5 m thick white ash with intercalations of marl and
limestone, can be followed throughout the basin and is used to record fossil levels both above and below it ; this Nivel Guia (guide level) corresponds to the fossil level named Calabozo Pata III (fig. 3). Fossil vertebrates are encountered sporadically throughout the basin, yet the richest concentration is found in a N N W - S S E strip located west of the Estancia Salla (fig. 2). The fossiliferous levels are
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concentrated within a 160 m section of the Estratos Salla that is situated I00 m above the base of the Estratos and 200 m below the top of the Estratos. Eight principal fossiliferous levels have been identified, and they can all be located with reference to the Nivel Guia {fig. 3). From oldest (lowest) to youngest (highest) these levels include the following localities (see fig. 3 ) : 1) laroyfilla; 2) Aramani Pata; 3) Calabozo Pata I, Poco Poconi I ; 4) Calabozo Pata I I ; 5) Calabozo Pata III (Nivel Guia); 6) Poco Poconi II ; 7) Tapial Pampa (= Tapilaya), Khara Tranca Pata, Poco Poconi Ill, Kollpa Jahuira: and 8) Cebadal Churu, Huichinca, Totoma, Huaykhallami.
At several localities (e. 9. Calabozo Pata, Poco Poconi) multiple fossiliferous levels occur and they are identified by numbering them from bottom to
top (fig. 3). The highest (youngest) principal fossil level (Cebadal Churu, Huichinca. Toloma, Huay- khallami) (fig. 3) occurs within a 9 to 10 m thick section. It is composed of two beds, each 2 m thick, of calcareous marls separated by 5 to 6 m of a dark red, sandy clay. The dark red clays contrast sharply with the lighter beds of the Estratos below, and the darker beds of the Estra- tos above.
No detailed stratigraphic section with precise measurements of the Estratos SaIla is yet avai- lable. Nevertheless, it has been possible to esta- blish the relative positions of the different fossi- liferous levels based on an estimate of the stratigraphic distances separating them. The names used to designate the localities are regional names, not used on official maps. but readily known to local natives.
S Y S T E M A T I C S
Marsupials have been collected from beds of Deseadan age in the Salla-Luribay Basin (Hof- fstetter, 1968, 1976; Patterson 6 Marshall, 1978) and at Lacayani (Hoffstetter et al., 1971) on the Altiplano southwest of La Paz. These published reports document a rich and varied marsupial fauna, yet some of the taxa thus far described are known only from fragmentary material, and their anatomy and relationships with other taxa are poorly known. In an attempt to expand knowledge of the marsupials from the Salla-Luribay Basin we here describe four new specimens from the collection in the Divisi6n de Paleontologia del Servicio Geol6gico de Bolivia (GEOBOL), La Paz. Among these specimens is a new genus and species of Borhyaenidae, one referrable to the borhyaenid Notogale mitis, another to the palaeo- thentine Palaeothentes boliviensis, and the last apparently represents an enormous indeterminate palaeothentine, family Caeno!estidae.
All measurements are in millimeters (ram). The serial designation for cheek tooth number is based
1,2,3 1 ,2 ,3 ,4 on the dental formula P , M - - -
1,2,3 1 ,2 ,3 ,4 Abbreviations used in text and tables are: C, canine; I, incisor; L, length; M. molar; P, pre- molar; W, width. The chronology and usa qe of South American land mammal ages follows Marshall et aI., 1977.
Family BORHYAENIDAE AMEOrUNO, 1894
S u b f a m i l y Hathlyacyninae KIRSCH, 1977
Sallacyon n. gen.
ETYMOLOGY Salla-, for pueblo of Salla ; -cyon, Gr. for dog.
TYPE
SaUacyon ho[[stetteri n. sp.
DISTRIBUTION As for type and only known species, given
below.
DIAGNOSIS As for type and only known species, given
below.
Sallacyon hoffstetteri n. sp. (fig. 4)
ETYMOLOGY ho[[stetteri, for Professor Robert Hoffstetter
in recognition of his significant contribution to knowledge of the Deseadan vertebrate fauna in the Salla-Luribay Basin, Bolivia.
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T Y P E
G E O B O L no. SAL (Salla) 539, a fragment of a right mandibular ramus with posterior root of M~, M.,_ missing tip of protoconid, and M:~ missing tips of protoconid and paraconid (fig. 4).
HYPODIGM
Type only.
LOCALITY
Specific locality not recorded.
t " h
Fig. -t. - - Sallacyon ho~[rs:etteri n. gen. et sp. SAL 539 (type). a fragment of a r ight mandibular ramus with posterior root of M I, M.> (missing tip of proto- conid), and M 3 (missing tips of proto- conid and paraconid) : a. labial ; b. occlusal : c, lingual views. Scale 5 ram. Sallacyon ho[~stetteri n. .qen. et sp. SAL 539 (type), un fragment de branche horizontale droite de mandibule avec la racine post~rieure de M 1, IVI~ (le sore- met du protoconide manque) et M:I (le sommet du protoconide et du paraconide manque) : a, r u e labiale: b. vue occlu- sa le ; c, r u e linguale. Echel le : 5 ram.
MEASUREMENTS
M., L --- 5.1 ram, W ~ 2.5 ram; Ma L = 5 .4 m m , W ~ 3.1 r a m ; M~-:) L : 10 .6 m m ; depth of ramus below labial side of M~_ -- 7.0 mm, breadth of same ---- 3.6 ram.
DIAGNOSIS
Smallest known species of Deseadan Borhyae- nidae; similar in size and structure to Perathe- reutes pungens Ameghino, 1891 and slightly smaller than Sipalocyon gracilis Ameghino, 1887 from beds of Santacrucian (early Miocene) age of Argentina.
DESCRIPTION
A small mental foramen opens below anterior root of M, ; M~-3 with well developed anterobasal cingula : lack metaconid ; trigonid compressed laterally, protoconid considerably larger than paraconid ; trigonid and talonid subequal in breadth on M2, trigonid broader than trigonid on M.~; talonid well developed, basined with three distinct cusps of which hypoconid is slightly larger than hypoconulid and entoconid; weak but dis- tinct basal cingular shelf occurs along labial sur- face of hypoconid connecting hypoconulid with posterolabial edge of protoconid (fig. 4).
COMMENTS
L.G. Marshall (1981, p. 115) proposed that species of Perathereutes of Santacrucian age, and Sipalocyon of Colhuehuapian (]ate Oligocene) and Santacrucian age shared a common ancestor not shared with other known species of Hathlyacgni- nae. This view is reinforced by knowledge of Sallacyon which is virtually inseparable in size and comparable structural features from Perathe- reutes pungens, and is only slightly smaller and has a slightly larger talonid relative to trigonid than do known species of Sipalocyon (for compa- rative measurements see Marshall, 1981). W e therefore recognize Sallacyon as the probable Deseadan ancestor of Perathereutes and (or) Sipalocyon.
Genus Notogale LOOMIS, 1914
Notogale mitis (AMEGHINO, 1897)
(fig. 5) ?Pharsophorus mitis AMEGHINO, 1897, p. 504. Notogale mitts LOOMIS, 1914, p. 216, figs. 142,
tales << Bernadino Rivadavia ~,, Buenos Aires, Argentina) 52-368, fragment of a mandibular ramus with basal portions of M~_~ (figured by Patterson ~ Marshall, 1978, fig. 2; Marshall, 1981, fig. 49).
HYPODIGM
The type, the specimens listed by B. Patterson (5 L.G. Marshall 0978, p. 46) and LG. Marshall (1981, p. 66), and G E O B O L no. SAL (Salla) 668, greater part of a mandibular ramus with roots of
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Ix-s, base of C, P~ missing anterior part of crown, roots of P.,, Pa missing tip of crown, M~ and M.~ complete, M,~ missing tip of protoconid, anterior root of M4 present on left side ; and roots of It-~, base of C, roots of P~, Pz and P~ missing tips of crown, M1 missing posterior edge of talonid, M._, and Ma missing greater part of protoconid, and Ma missing talonid on right side (fig. 5).
LOCALITY The type and AC (Amherst College) specimens
listed by L.G. Marshall (1981. p. 66) are from Cabeza Blanca, Chubut Province, Argen t ina ; the PIA (Princeton Universi ty) specimens listed by L.G. Marshall (1981, p. 66) and SAL 668 are from the Salla-Luribay Basin but are without specific locality information.
AGE Deseadan.
REVISED DIAGNOSIS OF LOWER DENTITION AND MAN- DmLE BASED ON SAL 668
Lower dental formula 3, I, 3, 4 (fiq. 5) ; similar in size and structure to species of Cladosictis from beds of Colhuehuapian and Santacrucian age in Argen t ina ; enormous mental foramen below pos- terior root of Pl, smaller one below middle of Pa and below M:-e contact ; symphysis extends to point below middle of P,.,; Ii-a subequal in size, with I,~ more dorsal to I: and Iz : C well to mode- rately developed; Pl separated from C and P~ by distinct diastems; Px-a oriented along same axis as molar series; Pl not set obliquely in j aw ; P2 longer and narrower than P3; posterobasal heel faintly developed on Pl, better developed on P,~, larger on Ps ; small but distinct anterobasal cin- gulum developed on M2-4 (this region on MI swollen, but no distinct cingulum deve loped) ; metaconid absen t : talonid of M1 subequal in
Table 1. - - Measurements (in ram) of lower cheekteeth of Notos mitis, Mensurations (en ram) des dents jugales inf~rieures dc Notogale mitis.
Pl P'_, P:~ MI M.,. M:: M4 M:_4 P : -M: Specimen L W L W L W L W L W L W L W L L
M A C N 52-36~ . . . . ~ 6.5 m 3.3 m 7.5 --~ 3.3 - - - -
breadth to posterior end of t r igonid; talonids of M,,4 narrower than triflonids; talonids reduced relative to well developed trigonids, and not or only incipiently basined in unworn tee th ; MI-.~ talonids with small but distinct hypoconid, ento- conid, and hypoconul id ; M4 talonid essentially unicusped with enlarged hypoconulid dominant, minute entoconid, and hypoconid visible in unworn teeth.
CO,~'IMENTS
Notogale mitis is the most abundant species of marsupial known in the Salla fauna. It is similar in size (table 1) and structure (fig. 5) to species of Cladosictis from beds of Colhuehuapian and Santacrucian age in Argentina. SAL 668 is the most complete specimen of N . mitis yet known and it reinforces the probable ancestral position
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of the genus to Cladosictis as earlier suggested by B. Pat terson ~ L.G. Marshal l (1978) and L.G. Marshal l (1981) based on more f ragmenta ry material,
TYPE PU (Princeton Univers i ty) 21977. f ragment of
a right mandibular ramus with Pa-Mt (missing posterolinflual corner of Mj ; figured by Pat terson 6 Marshall . 1978. fig. 19 ; Marshall . 1980, fig. 27).
Fig. 5. - - Notogale mitis (AMEGHINO, 1897, p. 504). SAL 668, greater part of a right mandibular ramus with roots or partial crowns of IvM(: a. labial: b. occlusal; c, lingual views. Scale ~, 10 ram.
Notogule mitis (AMEc, lUNO, 1897, p. 504). SAL 668. pattie principale de la branche horizontale droite de mandibule avec les racines ou les couronnes incomplbtes de II-M 4 a. rue labiale: b, vt,e occlusale: c, rue linguale. Echelle' 10 ram.
HYPODIGM T y p e and G E O B O L no. S A L (Salla) 621 (figs.
6, 7). fragment of a right maxil lary with roots of po, pa_M.~ complete, partial alveoli of M4: lefl
Table 2. -- Measurements {in mm) of cheek teeth of Palaeothen:cs boliviensis. Mensuration.~ (en ram) des dents jugales de Palaeothentes bolivier~is.
P3 MI M2 M3 M4 M I - 4 P3-M4 Specimen L W L W L W L W L W L L
Upper Dentition
SAL 621 (1) 5.5 3.0 't.4 't.9 3.6 4.7 - - - -
SAL 621 (r) 5.4 2.8 4.6 4.8 3.7 4.7 2.4 3.2
Lower Dentition
PU 21977 (type) 2.6 2.2 5.2 3.0 . . . . .
SAL 621 (1) 2.8 2.3 5.8 3.2 4.3 3.2 3.0 2.5
SAL 621 (r) 2.8 2.4 5.7 3.3 - - - - 2.9 2.6
m
2.3 1.9 15.0 17.9
2.1 2.0 15.0 17.7
maxil lary f ragment with roots of P~, P~-M" complete, and alveoli of M~-+; partial left mandi- bular ramus with Pa-M~ (Mr-3 missing postero- ling'ual c o r n e r s ) ; partial right mandibular ramus with anterior edge of M,_, present ; and an isolated upper right incisor.
LOCAI.ITY
SAL 621 is from Tapia l Pampa (fig. 2, F-5) .
DIAGNOSIS Large palaeothentine (table 2) ; P,~ ~ in height
to M~ trigonid ; smaller than Palacothentes chubu-
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tensis ; cons iderab ly larger and with more promi- nent Ps than con t emporaneous Pa laeo then t e s lucina and A c d e s t i s praecursor ; M~-q higher c rowned than in o ther known Palaeo then t inae .
DESCRIPTION Small but distinct mental foramen below middle
of M 1 ; ventral edge of mandibular ramus mar- ked ly convex ; depth of ramus below labial side of M~ = 7.2 mm, b read th of same = 3.7 m m : Ps two rooted, large, equal in height to t r igonid of M~ : poster ior end of Ps much broader than ante- rior end, and with small cuspule on anter ior edge about m i d w a y up c rown ; M~ tr igonid only sl ightly higher than t a lon id ; Mj paraconid b i furcated (sensu Marshal l , 1 9 8 0 ) : on M H lingual cusps h igher and more distinct than labial c u s p s : talo- nids wider than t r igonids on M~-4: infraorbital foramen opens over center of Po ; P" tiny. two rooted (as seen from partial roots on right maxil- l a r y ) : ps two rooted, lar.qe, anter ior root larger
A~ /
q ~
Fig. 6. - - Palaeothentes boliviensis PATTERSON ~ M,~RSHALL, 1978, p. 83. SAL 621, a partial left mandibular ramus with Pa-M 4 (MI_ s missing posterolingual corners): a, labial; b, occlusal; c, lingual views. Scale - 5 ram.
Palaeothentes boliviensis PA'rTEaSON ~ M,~USHALL, 1978. p. 83. SAL 621. branche horizontale gauche de mandibule avec P~-M 4 (le coin post~rolingual de MI_ a manque): a, rue tabiale; b, rue occlusale; c, rue linguale. Echelle: 5 ram.
than poster ior root. c rown slightly b roader poste- r iorly than anter ior ly (but c rown cons iderably na r rower and more e longate than in o ther Palaeo- t hen t i nae ) , and c rown about same height as M1 ; pa c rown tilted toward M 1, lacks enamel along posterol ingual edge, enamel thin a long anterol in- gual edge : M TM cons iderably h igher c r o w n e d than in o ther Palaeo then t inae , sharp decrease in size from M 1 to M ~ ; ends of M 1 subequal in breadth ; anter ior ends of M 23 marked ly wider than poste- rior e n d s ; labial sides of c rowns of M la higher than lingual s ides : c rown of M ~ not preserved, but three rooted as evidenced by alveoli (figs. 6, 7).
t
Fig. 7. - - Palaeothentes boliviensis PAT- TERSON ~ MARSHALL, 1978, p. 83. SAL 621, a right maxillary with P'~-MS: a, labial; b, occlusal; c, lingual views. Scale ~ 5 ram.
Palaeothentes boliviensis PATTERSON MARSHALL, 1978, p. 83. SAL 621, maxil- laire droit avec pS-Ma : a, rue labiale ; b, rue occlusale ; c. rue linguale. Echelle: 5 ram.
COMMENTS P a l a e o t h e n t e s bol iviensis was previous ly k n o w n
only from its type. a f ragment of a r ight mandi- bular ramus with Pa-M1. T h e d iscovery of S A L 621 adds grea t ly to our knowledge of the a n a t o m y of this species and helps clar i fy its possible af f in i ty with o ther known Palaeo then t inae .
14
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Palaeothentes boliviensis is smaller than P. chubutensis (AMV.GmNO, 1897) from beds of Deseadan age of Patagonia , southern Argentina, and P. aratae AMEGHINO, 1887 from beds of San- tacrucian age of P a t a g o n i a ; it is markedly larger than other named species of Palaeothent inae (for comparat ive measurements see Marshall , 1980). P. boliviensis differs from other Palaeothentinae in having markedly higher crowned molars, and in pa being considerably nar rower (more bladelike) and in lacking enamel along its posterolingual surface. These features demonstra te that P. boli- viensis is more specialized than other Palaeothen- tinae for dealing with an abrasive food source. P. boliviensis is thus too specialized to be ancestral to any later known palaeothentine.
B. Pat terson 6 L.G. Marshal l (1978, p. 90) des- cribed a very f ragmenta ry left mandibular ramus from Salla as probably representing a large poly- dolopoid. W e feel that the criteria used by B. Pat terson ~ L.G. Marshal l in assigning this spe- cimen to that marsupial group is valid, al though it is difficult to conceive that a palaeothentine and a polydolopoid of similar size should and could coexist in the same fauna. T h e possibility thus exists that the specimen described by B. Pat terson
L.G. Marshal l may represent the lower dentition of the same specimen as represented by GB 088 which is apparent ly not a polydolopoid but a palaeothentine. Clarification of this possibility must, however, await the discovery of more com- plete specimens, including associated upper and lower dentitions.
? Palaeothentinae gen . e t sp . i n d e t .
G E O B C ) L no. GB 088, a f ragment of a right maxil lary with P~-M 4 lacking all traces of enamel and deeply worn (fig. 8) is apparent ly a palaeo- thentine. It is from the << nivel superior >> at Kollu Huichinca (fig. 2, F-8) .
A large infraorbital foramen opens over the posterior root of pa. p3 is two rooted and the axis of the crown is oriented in the same axis as M 14 with the anterior root larger than the posterior root and the posterior end of the tooth broader than the anterior .A large inclined wear surface occurs along the posterolingual surface of p8 and is confluent with the wear surface on M s. A sharp size decrease occurs from M 1 to M 4. T h e occlusal shape of M 1; is similar to other Pa/aeo- thentinae - - the labial sides of the teeth are higher than the lingual s ides ; the anterior end of M ~ is subequal to or is slightly broader than the poste- rior e n d ; and the anterior ends of M '~a are notably broader than the posterior ends (M 4 is too poorly preserved to comment on) .
GB 088 compares structural ly with other Pa /aeo- thentinae and differs primarily in its enormous size. It is about twice as large as the Santacrucian species Palaeothentes aratae and the Deseadan species P. chubutensis, the largest palaeothen- tines known (see Marshal l , 1980). Linear tooth dimensions of GB 088 include P'~ L ----- 9.6 mm, W = 5.2 ram; M s L ---- 6.8 mm, W ~ 7.5 m m ; M 2 L --- 5.1 mm, W ~- 7.2 mm ; M 3 L ---- 3.8 mm, W --- 5.0 ram; M 1-~ L -- 17.'t ram; Pa-M4 L ~- 25.8 ram. Unfor tunate ly , this specimen is too f rag- menta ry to serve as a type, al though it clearly represents a new taxon.
Fig. 8. - - ?Palaeothentinae ten. et sp. indet. GB 088, a fragment of a right maxillary with P3-M4 very broken: a, labial; b, occlusal; c, lingual views. Scale -, 5 ram. ? Palaeothentinae ten. et sp. ind~t. GB 088. maxillaire droit fragmentaire avec pa-M 4 tr~s endommag~es: a. rue labia|e; b, rue occlusale ; c, rue linguale. Echelle : 5 ram.
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A c k n o w l e d g m e n t s
Aspects of this study were supported by the Gordon Science Foundation Grant DEB-7901976 to LGM. The Barbour Fund of Princeton University. and by National figures of specimens were drawn by Elizabeth Liebman.
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