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Ichnotaxonomic revision of Ameghinichnus, a mammalian ichnogenus from the Middle Jurassic La Matilde Formation, Santa Cruz province, Argentina
SILVINA DE VALAISMuseo Patagónico de Ciencias Naturales, Av. Roca 1280, (8332), General Roca, Río Negro, Argentina. Fax: 54-2941-420030. E-mail: [email protected]
Abstract
The ichnological assemblage from the Estancia Laguna Manantiales, from the Middle Jurassic La Matilde Formation, Santa Cruz province, Argentina, is exceptional both in diversity and abundance. It is composed of mammal, dinosaur, invertebrate, and root traces. The most significant and abundant specimens are those assigned to the ichnogenus Ameghinichnus Casamiquela, 1961. This ichnogenus is revised and an emendation of its diagnosis is suggested. The inclusion of all the known specimens to the type ichnospecies, Ameghinichnus patagonicus Casamiquela, 1961, is challenged and some specimens are placed in a new ichnospecies, Ameghinichnus manantialensis isp. nov. Similar tracks from other ichnological localities worldwide were previously referred to Ameghinichnus, but only Eopentapodiscus(Ellenberger, 1970), from South Africa is considered as a junior synonym of Ameghinichnus. The ichnotaxobases used to classify tracks with mammalian affinities at ichnogeneric and ichnospecific levels are evaluated and re-assessed ichnotaxonomic criteria are proposed. Different criteria used to distinguish mammalian imprints from non-mammalian tracks are commented.
Key words: Ameghinichnus, ichnotaxonomy, mammal tracks, Jurassic, Argentina
Resúmen
La asociación icnológica de la Estancia Laguna Manantiales, de la Formación La Matilde, Jurásico Medio, provincia de Santa Cruz, Argentina, es excepcional tanto en diversidad como en abundancia. La misma est compuesta por trazas de mamíferos, dinosaurios, invertebrados y de raíces. Los especímenes más significativos y abundantes son aquellos correspondientes al icnogénero Ameghinichnus Casamiquela, 1961. Se revisa el icnogénero y se sugiere una enmienda a su diagnosis. Se cuestiona que todos los ejemplares pertenezcan a la icnoespecie tipo, Ameghinichnus patagonicusCasamiquela, 1961, y algunos especímenes son ubicados en una icnoespecie diferente, Ameghinichnus manantialensisisp. nov. Huellas similares provenientes de otras localidades icnológicas del mundo han sido previamente referidas a Ameghinichnus, pero sólo se considera sinónimo junior de Ameghinichnus a Eopentapodiscus (Ellenberger, 1970), de Sudáfrica. Se evalúan las icnotaxobases usadas para clasificar huellas con afinidad mamaliana a nivel icnogenérico e icnoespecífico, y se propone una nueva evaluación de los criterios icnotaxonómicos. Se discuten distintos criterios usados para diferenciar huellas mamalianas de las no mamalianas.
Palabras claves: Ameghinichnus, icnotaxonomía, huellas mamalianas, Jurásico, Argentina
Introduction
The first ichnotaxonomic studies of Jurassic tetrapod ichnofossils from Argentina were carried out by Casamiquela (1960, 1961, 1964), followed by more recent compilations of South American tetrapod tracks by Leonardi (1994) and Leonardi and de Oliveira Lima (1990).
Accepted by P. Gaubert: 22 Jul. 2009; published: 19 Aug. 2009 1
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The ichnological assemblage from the Jurassic La Matilde Formation, Santa Cruz province, Argentina, is the most significant in South America, both in terms of diversity and abundance, and is composed of mammal, dinosaur, invertebrate, and root traces (Casamiquela 1960, 1964; de Valais & Melchor 2003; de Valais et al. 2003; Coria & Paulina Caravajal 2004; Melchor et al. 2004; de Valais 2008). Probably the most significant and spectacular of these ichnotaxa is the ichnogenus Ameghinichnus Casamiquela, 1961, which is amongst the earliest evidence of mammalian activity in the whole fossil record (e.g. Martin & Rauhut 2005; Rougier et al. 2007a,b). Due to the importance of this assemblage, a modern ichnotaxonomical revision and a detailed study are required. The main goal of this contribution was therefore to present a comprehensive and updated ichnotaxonomic treatment of the ichnogenus Ameghinichnus from the Jurassic La Matilde Formation and to compare it with other similar mammalian and mammal-like ichnotaxa, thereby evaluating its stratigraphic distribution. Possible morphological and paleobiological characteristics of the trackmaker have also been inferred. This overview includes the revision of published and unpublished material both in situ and housed in different ichnological collections.
Materials and methods
Geological setting and stratigraphy
The La Matilde Formation covers an estimated area of approximately 20.000 km2 in the Santa Cruz province (Andreis et al. 1992), interdigitating both laterally and vertically with the Chon Aike Formation: together these two formations comprise the Bahía Laura Group (Stipanicic & Reig 1956; Lesta & Ferello 1972). The total thickness of the unit is estimated at 150 m - 200 m (Panza & Genini 1998). It is comprised of primary and reworked siliceous volcaniclastic sediments, mainly tuffs, lapilli-stone, tuffaceous sandstones and rare ignimbrites and breccias (e.g. de Barrio et al. 1999; Panza & Haller 2002), although interbedded lacustrine shales also occur in outcrops close to the Atlantic coast (e.g. Mazzoni et al. 1981). The formation has been interpreted as having formed in a lowland setting associated with an active volcanic environment, with swamps and water bodies probably derive from the adjacent floodplains (Mazzoni et al. 1981; Panza 1998; Melchor et al. 2004).
The formation has been dated on the basis on its fauna and flora fossil record (Stipanicic & Reig 1956; Stipanicic & Bonetti 1970), as well as radiometric dating of volcanics from the Chon Aike Formation (de Barrio et al. 1999), which together indicate a Callovian-Bajocian (Late Middle Jurassic) age, according to the time scale of Gradstein & Ogg (2004).
The ichnofossiliferous locality is situated at the Estancia Laguna Manantiales, 25 km northwest of the Petrified Forest Natural Monument of Jaramillo in Santa Cruz province, Argentina (Fig. 1). The strata here are almost horizontal with a measured thickness reaching up to 68 m (Melchor et al. 2004) and are overlain with angular discordance by the Aptian Bajo Tigre Formation, Baqueró Group (Andreis et al. 1992; Panza 1998; Cladera et al. 2002). The analyzed section includes primary ash-fall, reworked tuffs, welded tuffs, tuffaceous siltstones fine-grained sandstones, and rhyolitic ignimbrites (Melchor et al. 2004).
Until now, five different vertebrate ichnogenera have been recognized from the Estancia Laguna Manantiales locality. Casamiquela (1961, 1964) named and described Ameghinichnus patagonicus, related to mammal activity, and Delatorrichnus goyenechei, Sarmientichnus scagliai, and Wildeichnus navesi, assigned to dinosaurs. More recently, de Valais and Melchor (2003) mentioned the presence of footprints comparable to Grallator Hitchcock, 1858. Among the invertebrate ichnotaxa, the most abundant is Hexapodichnus casamiquelai de Valais, Melchor and Genise, 2003, likely assigned to a pterygote insect.
The first specimens recovered from the La Matilde Formation were collected during the 60s by Casamiquela (1960, 1964). The collection was later enlarged by Bonaparte and others (Casamiquela 2002; Melchor et al. 2004). Recently, expeditions carried out by the author and colleagues have yielded new specimens, increasing the available data from this ichnological locality.
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The specimens examined, both as natural molds and casts, are published and unpublished material housed in ichnological collections in Argentina. For the tracks not collected, plaster replicas were prepared. All measurements on the footprints follow the conventions and methodology of Leonardi (1987) and Thulborn (1990). The track and trackway measurements were taken as indicated in Figure 2, and summarized in Tables 1 and 2. General morphological features referred to the symmetry of the trackways follow the convention of Trewin (1994).
FIGURE 1. Location map of the Estancia Laguna Manantiales, Santa Cruz province, Argentina. The star indicates the ichnofossiliferous locality.
General Ichnotaxonomical and Ichnological ConsiderationsThe nomenclature of the trace fossils follows the International Code of Zoological Nomenclature (Fourth
edition 1999; ICZN). The earliest treatments of ichnotaxonomy interpreted the trace fossils as part of an animal or plant, usually introducing zoological or botanical terms in their diagnosis and descriptions. However, in 1961 the ICZN included the trace fossils or “work of an animal”.
In this contribution, the general ichnotaxomonic concepts of vertebrate trace fossils follow the criteria of Bertling et al. (2006) and de Valais and Melchor (2008). These concepts imply on a simplistic level that the ichnotaxonomical treatment must be based on morphological features of the footprints and trackways. This includes those features with anatomical and behavioural implications, and should be independent not only of the age of the footprint-bearing succession, but also the locality of provenance and the possible tracemaker of the trace fossil. Ideally, the erection of a new ichnotaxon should be based on a large sample size in order to consider the full variability of the footprint population (e.g. to establish the range of the length:width ratio of the track and the range of the angles among the digit impressions). The use of footprint size in vertebrate ichnotaxonomy as an ichnotaxobase (morphological characteristics for ichnotaxonomical identification; Bromley 1990) must be restricted to an ichnospecific level, but always in association with other characteristics.
Ichnotaxonomical considerations of mammal and mammal-like tracksThe biological diversity achieved by the different groups of mammals in their evolutionary history results
in a high ichnological diversity that makes the study of tracks a very complex endeavour (e.g. Murie 1974; Rezendes 1995). Consequently, it is almost impossible to try to distinguish a set of ichnotaxobases at
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ichnogenerical and ichnospecifical levels applicable to all the taxonomic groups inside Mammalia. The present ichnotaxonomical approach refers only to tracks produced by a purported basal or primitive, conservative foot structure. Thus, it is considered that the basal mammals would have been, according to the vertebrate track record, small-sized, quadrupedal and erect animals, having fore and hindlimbs with subequal and pentadactyl manus and pes (e.g. Ji et al. 2002 and references therein; Kielan-Jaworowska & Hurum 2006; Rougier 2002). It is important to consider that the primitive pentadactyl trackmaker could have had a functionally tetradactyl, or even tridactyl or didactyl, manus and pes, but this particular functionality is not discussed here.
The ichnotaxobases used by different authors to classify mammal and mammal-like footprints, both at ichnogenerical and ichnospecifical levels are varied (e.g. Vialov 1966; Scrivner & Bottjer 1986; Sarjeant & Langston 1994; Lockley & Foster 2003; McCrea et al. 2004). In this study, considering the previously mentioned concepts, the ichnogeneric taxobases proposed are: 1) general morphology of the tracks, 2) number, orientation and morphology of the digit imprints, 3) relative positions and size difference between manus and pes impressions, and 4) presence or absence of phalangeal pads and tail marks. These features, allowing to differentiate mammals and mammal-like tracks at the ichnogenerical level, take into account mostly the qualitative aspects of the analyzed tracks.
TABLE 1. Summary of measurements of track and trackway parameters of Ameghinichnus patagonicus and A.
manantialensis. Linear measurements in millimeters. For abbreviations, see Figure 2.
The ichnospecific taxobases proposed herein are: 1) range of length:width ratio of hind and forefoot, 2) rotation of the tracks in relation to the midline, 3) proportion of digit lengths, 4) range of the angles between the digit impressions, 5) presence and shape of claw marks, and 6) pace angulation and stride length. These
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features, allowing to separate mammal and mammal-like tracks in an ichnospecifical level, take into account the quantitative aspects of the tracks.
Institutional Abbreviations
MACN Colección de Paleontología de Vertebrados del Museo Argentino de Ciencias Naturales “Bernardino Rivadavia” (-SC, Santa Cruz Collection), Buenos Aires, Argentina
MLP Museo de La Plata, La Plata, Buenos Aires province, ArgentinaMPEF-IC Colección de Icnología del Museo Paleontológico “Egidio Feruglio”, Trelew, Chubut
province, ArgentinaMPM-PIc Colección de Icnología del Museo Regional Provincial “Padre Manuel Jesús Molina”, Río
Gallegos, Santa Cruz province, Argentina PVL Colección de Paleontología de Vertebrados del Instituto Miguel Lillo, San Miguel de
Tucumán, Tucumán province, Argentina
FIGURE 2. Diagram with the conventions of footprint and trackway measurements used in this paper. A, parameters corresponding to the tracks; B, parameters corresponding to trackways with alternate arrangement of the manus-pes sets; C, parameters corresponding to trackways with opposite arrangement of the manus-pes sets; D, detail of the measured angles between the impression of the digits. Abbreviations: L, track length, distance between the distal tip of digit III and the proximal boundary of the sole; TL, total track length, distance between the distal tip of digit III and the proximal boundary of the sole, taking into account the bilobate outline; W, track width, distance between the distal tip of digits I and V measured perpendicular to the track axis; I, length of digit I; II, length of digit II; III, length of digit III; IV, length of digit IV; V, length of digit V; I-II, angle formed by the axis of digits I and II; II-III, angle formed by the axis of digits II and III; III-IV, angle formed by the axis of digits III and IV; IV-V, angle formed by the axis of digits IV and V; I-V, angle formed by the axis of digits I and V; Pa, pace angulation, angle formed by the segments joining corresponding points of three consecutive tracks; SL, stride length, distance between the same point of two consecutive tracks on the same side of the trackway; H, hop, distance between the same point of two consecutive groups of manus-pes sets; DM, divarication of the track from the midline, angle formed by the longitudinal track axis with the midline; D mp, distance manus-pes, distance between the more distal boundary of the hand print and the more proximal boundary of the footprint; IW, inner trackway width between tracks, distance between the parallel, medial tangents to the closest tracks of two consecutive sets of opposite side, taking parallel to the midline; OW, outer trackway width between tracks, distance between the parallel, external tangents to the footprints, taking parallel to the midline.
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TABLE 2. Detailed measurements of track and trackway parameters of Ameghinichnus manantialensis. Linear measurements in millimeters. For abbreviations, see Figure 2.
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Type ichnospecies. Ameghinichnus patagonicus Casamiquela, 1961, from late Middle Jurassic, La Matilde Formation, Santa Cruz province, Argentina.
Emended diagnosis. Quadrupedal trackways with nearly homopod, symmetric, pentadactyl manus and pes impressions. The manus-pes sets of each body side display an alternate or opposite configuration in relation to the midline, always with the hand impressions located medially to the footprint and with inward rotation from midline. The footprints display outward rotation from midline, and are slightly larger than the handprints. Both manus and pes are wider than long, with the digit impressions straight. The length and angles between the digit imprints are subequal, and the angle between digits I-V is large. Tail mark often impressed, sinuous and continuous where tracks are in alternating arrangement, or straight and discrete where tracks are in opposite configuration.
Remarks and comparisons. The authorship of the ichnogenus Ameghinichnus and its type ichnospecies Ameghinichnus patagonicus is frequently referred to as Casamiquela, 1964 (e.g. Olsen & Galton 1984; Leonardi 1994; Sarjeant 2000). However, these names were mentioned the first time by Casamiquela (1960:
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12), with neither description of the imprints nor diagnosis, though the holotype is mentioned and illustrated, and there is a brief description of the possible trackmaker. The ICZN (Art. 13.1) does not validate an ichnotaxon published after 1930 without its corresponding description, therefore the name created by Casamiquela (1960) is here considered as a nomen nudum. This does not disqualify it from being used later as a valid name, such as Casamiquela (1961) does, where the author presents a suitable description of the ichnotaxon, satisfying the requirements of the ICZN.
Deposits of the Upper Triassic-Lower Jurassic Elliot Formation, from the Karoo basin of South Africa, have yielded an abundant ichnofauna with several vertebrate ichnotaxa displaying different degrees of affinity with Ameghinichnus (Ellenberger 1970, 1972, 1974, 1975; Olsen & Galton 1984). Olsen and Galton (1984) revised these ichnotaxa and synonymized several specimens originally in different ichnotaxa under the ichnogenus Ameghinichnus which they regarded as a subjective junior synonym. These ichnotaxa are, in alphabetical order: Acropentapodiscus, Amphibiopodiscus, Aristopentapodiscus, Dicynodontipus (= Calibarichnus), Dinopentapodiscus , Eoameghinichnus (= Ameghinichnus), Eopentapodiscus , Grypopentapodiscus, and Pseudameghinichnus (= Ameghinichnus).
Herein, a new ichnotaxonomical analysis of this South African ichnofauna is considered, and the ichnotaxa Amphibiopus, Aristopentapodiscus and Calibarichnus are considered distinct (i.e. not synonym with) from Ameghinichnus. The reasons are as follows:
Ameghinichnus is distinguishable from Amphibiopodiscus Ellenberger, 1970 (Amphibiopus in errore by Olsen & Galton 1984), which is represented by moderately preserved tracks and few morphological details. It displays pentadactyl manus and pes impressions like Ameghinichnus but with outward curved digit impressions and no sole marks (i.e. metatarsal or metacarpal impressions and posterior sole margin), even in deep impressed tracks (Ellenberger 1970, 1974).
Aristopentapodiscus Ellenberger, 1970 displays pentadactyl manus and pes impressions, but it differs from Ameghinichnus by having long and acuminate digit imprints, often lightly curved, and low total divarication (Ellenberger 1970, 1975).
A manus-pes set was originally included in Calibarichnus Casamiquela, 1964 by Ellenberger (1970). Melchor and de Valais (2006) have referred this ichnogenus to Dicynodontipus Lilienstern, 1944, on the basis of its general morphology (i.e. pentadactyly, digit impressions anteriorly directed comprising similar, low angles). The inclusion of the specimen in Dicynodontipus is accepted, thus it is excluded from Ameghinichnus.
With regard to Eopentapodiscus Ellenberger, 1970, it contains relatively large symmetrical tracks, with subequal and splayed digit imprints, and manus and pes impressions that are both subequal in size and shape, matching the Ameghinichnus diagnosis. So, the interpretation of Eopentapodiscus as a junior synonym of Ameghinichnus is accepted.
It was not possible to be confident about the position of Grypopentapodiscus, Acropentapodiscus, Dinopentapodiscus, Eoameghinichnus, and Pseudameghinichnus with regard to Ameghinichnus because of the following criteria. Olsen and Galton (1984) compared Ameghinichnus with Grypopentapodiscus (= cf. Aristopentapodiscus) (Ellenberger, 1970). The general morphology of the tracks of the latter ichnogenus is similar to Ameghinichnus, with a pentadactyl footprint but with a relatively larger length:width ratio and a lower total divarication (Ellenberger 1970, 1975). However, the lack of proper descriptions and illustrations, make the ichnotaxonomical comparisons with Ameghinichnus difficult and inconclusive.
Acropentapodiscus Ellenberger, 1970 is composed of tracks with a variable general morphology with poor to moderate preservation, mainly with digit imprints and few general details (Ellenberger 1970, 1975). Dinopentapodiscus Ellenberger, 1970 displays a similar general aspect to Ameghinichnus (Ellenberger 1970, 1975), but the poor preservation prevents the analysis of the whole track morphology and its details. The specimens included in Pseudameghinichnus (Ellenberger 1970), originally placed as Ameghinichnus and later assigned to Pseudameghinichnus (Ellenberger 1975), are rounded in shape and poorly preserved limiting a clear differentiation between the impressions of the digits (Ellenberger 1970, 1975). Eoameghinichnus(Ellenberger, 1970) was erected on the basis of a single specimen, originally designed as Ameghinichnus, and
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reassigned to the new ichnogenus by Ellenberger (1975) due to its size being five times that of the other known specimens of Ameghinichnus. This single specimen is a deep and partially preserved track, with only three digit impressions visible (Ellenberger 1970, 1975). Thus, a confident ichnotaxonomical assignment for these ichnotaxa is not possible here.
Besides the specimens from the Karoo basin, other mentions of materials referred to Ameghinichnus are present in the literature. Several manus and pes sets from the Towaco Formation (Lower Jurassic) of the Newark basin, USA, have been assigned to Ameghinichnus isp. (see Olsen & Rainforth 2001, and references therein). They display a general morphology very similar to those of Ameghinichnus, with pentadactyl tracks and wide spread between digits I-V with phalangeal pads and rare claw marks. Lockley et al. (2004) have accepted this assignment to Ameghinichnus, an opinion shared herein.
Gierliński et al. (2004, 2005) presented a relatively larger pentadactyl track, as long as wide, poorly preserved, from the Lower Jurassic of Sołtyków, Poland, and compared it with Ameghinichnus. The specimen displays a similar morphology to those included in the ichnogenus, but the preservation of the track prevents an ichnotaxonomical assigment with confidence. Thus, the Polish specimen is provisionally included in the ichnogenus until better preserved specimens allow confirmation or refutation of the proposed affinities with Ameghinichnus.
Holotype. MLP 60-X-31-14A, trackways with six manus-pes sets with opposite arrangement about the midline (associated with the paratype MLP 60-X-31-14B) (trackway 1 in Figs. 3b, 3e).
Emended diagnosis. Ameghinichnus preserved as manus and pes tracks with a length:width ratio of 0.7. Manus digit impressions are subequal in length, with a relative digit length: I<II=V<IV<III, angles between III-IV<I-II≈II-III≈IV-V, I-V averages 151º. Manus impressions display an inward rotation of about -16º in relation to the midline, and are located aligned-to-posterior to pes impressions. Pes digit impressions are subequal in length, with relative length: I<IV≈III=V<II, angles between III-IV<II-III<I-II<IV-V, I-V averages 152º. Pes display an outward rotation of about 31º in relation to the midline. Claw marks are absent and there are no marked phalangeal pads. When manus-pes sets display alternate arrangement about the midline, manus and pes pace angulation is about 143º and 114º, respectively, and manus and pes stride length is about 83 mm and 81.2 mm, respectively.
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FIGURE 3. Photographs of the type series of Ameghinichnus patagonicus. A, MLP 60-X-31-1; B, MLP 60-X-31-14B, holotype (right trackway: 1) and MLP 60-X-31-14A, paratype (left trackway: 2), the black arrows indicate the moving direction of the trackmaker; C, PVL 2303; D, PVL 2302, the white arrow indicates the bilobate outline; E, detail of the two first manus-pes sets of MLP 60-X-31-14B; F, MLP 60-X-31-15; G, MLP 60-X-31-3. A-C, D, F and G, paratypes. Scale bars: 2 cm in D and E, 5 cm in the rest. m, manus imprint; p, pes imprint.
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FIGURE 4. Photographs of specimens of Ameghinichnus patagonicus. A, MPM-PIc-3768 (first manus-pes set to the left) and 3769 (first manus-pes set to the right); B, MPEF-IC 1016 at left, indicated with a 1, MPEF-IC 1015 at rigth, indicated with a 2; C, MPEF-IC 1023; D, MACN 18619; E, MPEF-IC 1041; F, MACN-SC 4354; G, MACN 18622, the white arrows indicate the bilobate outline; H, detail of the third manus-pes sets of MPM-PIc-3952; I, MPM-PIc-3952. Scale bars: 2 cm in C, E, F, and H, 5 cm in A, D, G, and I, and 10 cm in B. The black arrow in C, E, and F indicates the tail mark. m, manus imprint; p, pes imprint.
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Remarks and comparisons. The ichnospecies Ameghinichnus mirabilis (Ellenberger, 1970) nov. comb., from the Elliot Formation in the Karoo basin, is composed of large-sized, symmetric manus and pes impressions subequal in size, with digit imprints splayed and subequal in length. Ameghinichnus patagonicusdisplays a track morphology comparable to A. mirabilis, but as it lacks the trackway parameters and is larger in size. It is not possible to assure the synonymy between both ichnospecies.
Ameghinichnus patagonicus can be distinguished from the specimens from the Newark basin, USA, mentioned as Ameghinichnus n. isp. by Olsen and Rainforth (2001: fig. 59) by their lack of the sharp claw marks, as well as being almost half the size.
The specimen presented by Gierliński et al. (2004, 2005) from the Lower Jurassic of Sołtyków, Poland, is interpreted here as a left track. It lacks sufficient details to make a comparison with Ameghinichnus patagonicus to define an ichnotaxonomical relationship.
Description. The specimens of Ameghinichnus patagonicus are represented by numerous tracks and trackways produced by a quadrupedal trackmaker. Table 1 summarizes the measurements from 28 trackways accounting for 405 imprints.
The trackways are composed of manus-pes sets, both pentadactyl tracks, which are nearly symmetrical in relation to the major imprint axis. Manus and pes digit impressions are slender, with a maximum width up to 1.5 mm and may be parallel-sided. They lack phalangeal pads and claw marks, though have a distal swelling.
The average width and length of the hand impressions are 11.5 mm and 8.2 mm, respectively. Digit impressions are subequal in size and shape, with an average length, in decreasing order, of: I: 2.8 mm, II and V: 3.2 mm, IV: 3.4 mm, and III: 3.5 mm. The angles formed by them are relatively equidistant, having an average of: I-II: 42º, II-III: 42º, III-IV: 37º, and IV-V: 42º; the I-V displays an angle with a mean of 151º. Manus imprints show an outward (negative) rotation relative to the midline, with a mean of -16º.
The average width of the footprints is 13 mm, while the average length is 9 mm. Digit impressions are subequal as in the case of the manus, with an average length of: I: 3.0 mm, IV: 3.6 mm, III and V: 3.7 mm, and II: 4.0 mm. The average angles formed by them are as follows: I-II: 42º, II-III: 30º, III-IV: 26º, and IV-V: 58º; the I–V displays an angle with a mean of 152º. Pes imprints show an inward (positive) rotation relative to the midline with an average of 31º.
Both manus and pes sole display metacarpal and metatarsal imprints, a posterocentered depression, and a posterior bilobate outline which is only visible in the best- preserved tracks. When this posterior bilobated outline is present, the length of the track (named here as total length, see figure 2) is about 9.2 mm for hand prints and 10.9 mm for footprints (Figs. 3d, 4g).
The manus-pes sets can display two arrangements: either ipsilateral with the manus and pes imprints on the same side of the body of the trackmaker in alternate arrangement (sensu Trewin 1994; e.g. Figs. 3a,g), or both sets accounting the four limbs of the trackmaker in a transverse group as opposite arrangement (sensu Trewin 1994), with one manus and pes set on one side, opposite the corresponding pair on the other side (e.g. Fig. 3e, trackway 2 in 4b). In both cases, the footprints are located externally and overstep or slightly overlap the manus.
When the sets have an alternate arrangement, the trackways display an average pace angulation of 143º for the manus, and of 114º for the pes. The average stride length of the manus and pes imprints is 83 mm and 81.2 mm, respectively. The inner trackway width between manus imprints averages 2.7 mm, and the width between footprints averages of 17.5 mm, whereas the average outer trackways width is 23.6 mm for manus and 38.8 mm for pes.
When the sets have a transverse or opposite arrangement, the distance between two consecutive groups, named herein as a hop or jump, displays a mean of 91.6 mm.
The trackways may show tail marks, in a continuous and curved or sinuous pattern when the sets have an alternative arrangement (e.g. Fig. 4c, trackway 1 in 4b), or discrete (average length of 7.7 mm) and straight when they are opposite (e.g. Fig. 4e, trackway 2 in 4b). Both kinds of tail marks have an average width of 4.1 mm.
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Holotype. MPEF-IC 1028, trackways with three manus-pes sets with alternate arrangement about the midline (Fig. 5a).
Paratypes. MLP 60-X-31-13, 65-XI-12-1 (three slabs with the same collection number), MPM-Pic-2098 (Figs. 5b–e).
Etymology. Manantialensis (Latin), in reference to the Estancia Laguna Manantiales (Santa Cruz province, Argentina), the locality where the footprints were discovered.
Diagnosis. Ameghinichnus preserved as manus and pes tracks with a length:width ratio of 0.7 and 0.6 respectively. Manus digit impressions are subequal in length, with relative digit length: I<V<IV<II≈III, angles between between II-III<III-IV<I-II˜IV-V. Manus impressions display an inward rotation of about -38° in relation to the midline, and are located aligned to anteriorly to pes. Pes digit impressions are subequal in length, with relative length: I< III<IV≈V<II, angles between III-IV<II-III<I-II<IV-V. Pes impressions display an outward rotation of about 26° in relation to the midline. Both I–V angles for pes and manus are about 107°. Claw marks are absent and there are no evident phalangeal pads. When manus-pes sets display an alternating arrangement about the midline, manus and pes pace angulation averages 156° and 110º respectively, and manus and pes stride length is about 116 mm and 119 mm respectively.
Remarks and comparisons. The morphology of these tracks allows them to be included in the ichnogenus Ameghinichnus: quadrupedal trackways with symmetric pentadactyl manus and pes impressions, manus slightly smaller than pes, subequal and splayed digit impressions. But given its particular features, this group of tracks is different enough from the other specimens of the ichnogenus to deserve a separate ichnospecies level designation. A. manantialensis differs from A. patagonicus by having different digit length proportions and divarication angles, and the manus located aligned-to-anterior to the pes impression. In addition, the impressions of the hands are, on average, 63 % longer and 60 % wider relative to Ameghinichnus patagonicus, whereas the footprints are, on average, 50 % longer and 72 % wider.
The tracks assigned to Ameghinichnus isp. from the Lower Jurassic Newark basin of USA (see Olsen & Rainforth 2001, and references therein) differ from A. manantialensis in the presence of clear sharp claw marks in some of the digits. This could be preservation differences due to sediment texture (e.g. mud or sand), and more specimens are needed to define the assignation of the tracks.
Ameghinichnus mirabilis (Ellenberger, 1970) nov. comb., from the Upper Triassic-Lower Jurassic Karoo basin of South Africa, differs from the new ichnospecies in having different proportion in the length of the digit imprints. However, an ichnotaxonomical assignment is uncertain, taking into consideration that the trackway parameters of A. mirabilis are unknown.
The left footprint from the Lower Jurassic of Sołtyków, Poland (Gierliński et al. 2004, 2005) is similar to Ameghinichnus manantialensis due to the angles between the digit impressions, but as a result of the scarse details, it is not possible to make a confident comparison with the new ichnospecies.
Description. The specimens are represented by three trackways, with a total of seventeen tracks, and two isolated manus-pes sets, produced by a quadrupedal trackmaker. Their measurements are summarized in Table 1 and detailed in Table 2.
The manus-pes sets, both pentadactyl and digitigrade to semidigitigrade tracks, are nearly symmetrical in relation to the major imprint axis. Manus and pes digit impressions are slender, with a maximum width up to 2 mm, and may display a parallel outline, exhibiting a distal swelling. They lack phalangeal pads and claw marks. Plantar and sole impressions display similar features to Ameghinichnus patagonicus (i.e. with metacarpal or metatarsal imprints, a posterocentered depression, and a posterior bilobate outline which is rarely visible).
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FIGURE 5. A–E, photographs of specimens of Ameghinichnus manantialensis. A, MPEF-IC 1028, holotype; B, MLP 65-XI-12-1; C, MLP 65-XI-12-1; D, MLP 60-X-31-13, the black arrow indicates the specimen; E, MPM-Pic-2098; B-E, paratypes; F, MPM-PIc-3957, Ameghinichnus? isp. Scale bars: 2 cm in F, and H, and 5 cm in the rest. m, manus imprint; p, pes imprint.
The hand impressions range from 17.8 mm to 20.6 mm wide, with an average of 18.9 mm, from 12.6 mm to 15.1 mm long, with an average of 13.7 mm, and about 16 mm total length. Digit impressions are subequal in size and shape, with an average length, in decreasing order, of: I: 4.2 mm, V: 5.2 mm, IV: 5.7 mm, II: 6.3 mm, and III: 6.4 mm. The angles formed by the digit imprints are relatively equidistant, having an average of:
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I-II: 35°, II-III: 22°, III-IV: 26°, and IV-V: 34°; the I-V angle ranges from 102° to 110°, with an average of 107°. Manus imprints show an outward rotation relative to the midline, which ranges from -32° to -40°, with a mean of -38°.
The footprints range from 20.5 mm and 25.8 mm wide, with an average of 22.3 mm, from 12.6 mm to 18.0 mm long, with an average of 14.3 mm, and about 17.1 mm total long. Digit impressions are subequal as in the case of the manus, but with an average length of: I: 5.0 mm, III: 5.5 mm, IV≈V: 5.8 mm and 5.9 mm, respectively, and II: 6.1 mm. The angles formed average: I-II: 35°, II-III: 29°, III-IV: 16°, and IV-V: 40°; the I-V displays an angle from 101° to 117°, with an average of 107°. Pes imprints show an inward rotation relative to the midline, which ranges from 8° to 41°, with a mean of 26°.
The specimens display only one arrangement, with the ipsilateral manus and pes imprints in alternating configuration. There is no trackway displaying an opposite arrangement, possibly due to preservation bias in this small sample. The hand imprints are located aligned or anterior and medial to the footprints and may even touch them. The inner trackway width between opposite manus imprints is about -8 mm, and the width between pes is about 20.5 mm. The average outer trackway width is 28.7 mm and 61.4 mm for hand imprints and footprints, respectively. The pace angulation ranges from 146° to 160°, with an average angle of 156° for the manus, and only one measurement of 110° for the pes. The stride length ranges from 99 mm to 119 mm, with a mean of 110.4 mm for the manus, and 109.5 mm for the pes. The inner trackway width between manus and pes is about -8 mm, and 20.5 mm, respectively. The outer trackway width is 28.7 mm for manus and 61.4 mm for pes.
Ameghinichnus? isp.Figure 5f
Materials. MPM-PIc-3957.Description. Specimen MPM-PIc-3957 is a poorly preserved partial imprint, where the lack of details
makes it impossible to distinguish if it is a hand or a pes impression. The track is 23 mm long and, as preserved, 18.1 mm wide. The only complete digit impression is III which is 14.7 mm long. It also presents partially preserved impressions of digits II and IV. There are no phalangeal pads or claw marks.
Remarks. The morphology of the preserved portion of the track is similar to Ameghinichnus, but the ichnotaxonomical assignment is uncertain. In addition, it is twice as large as the average for Ameghinichnus patagonicus, for which reason this track is here described.
Specimen with uncertain ichnogenerical assignment
Material. MPEF-IC 1039, its uncollected mould, and a plaster cast (MPEF-IC 1042; Fig. 6a).Description. MPEF-IC 1039 is a natural cast of an uncollected trackway, preserved as positive hypichnia.
The trackway is composed of eight elongated oblique possible subtracks. The traces range from 48.7 mm to 54 mm long, with a mean of 50.2 mm, and from 20.3 mm to 23.5 mm wide, with a mean of 22.6 mm. The outer trackway width averages 88 mm, whereas the inner trackway width averages 36 mm. The averages of the stride length and the pace angulation are 163 mm and 108°, respectively.
Remarks. The specimen lacks morphological details to make an ichnotaxonomical assignment. On the basis of its general aspect, the specimen resembles Ameghinichnus where each elongated trace corresponds to a very deep undertrack of an ipsilateral manus-pes set. If this interpretation is correct, the traces display an outward rotation in relation to the midline, and the sense of movement of the trackmaker on Fig. 6a is from a to b. Some trackways comparable to specimen MPEF-IC 1039 were observed in preliminary neoichnological studies in modern small mammals in the Playa Fracasso, Chubut province, Argentina. In these cases, quadruped mammals impressed the tracks of their four limbs in an apparent bipedal configuration (Fig. 6b).
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FIGURE 6. Comparison between an ichnofossil and a modern trackway. A, MPEF-IC 1042, plaster cast of the uncollected specimen with uncertain ichnogenerical assignment. The movement direction of the trackmaker is from a to b; B, trackway made by a quadruped mammal with an apparent bipedal disposition, from Playa Fracasso, Chubut province, Argentina. Scale bar: 10 cm.
Discussion
Stratigraphic distribution of AmeghinichnusIn the vertebrate track record from the Triassic, footprints assigned to small-sized therapsids (i.e.
Dicynodontipus von Lilienstern 1944) are widely distributed in outcrops from Argentina (Melchor & de Valais 2006, and references therein). They were entirely replaced in the Jurassic by purported true mammals with a highly developed locomotion system, as represented by Ameghinichnus, the most abundant component of the La Matilde ichnofauna. Besides the most numerous and previously known ichnospecies A. patagonicusCasamiquela, 1961, a set of larger tracks is assigned herein to the new ichnospecies, A. manantialensis.
Another three ichnological assemblages from the Jurassic have yielded specimens assigned to Ameghinichnus, though their facies and paleoenvironment are rather different. The first finding corresponds to several manus-pes sets assigned to Ameghinichnus from the Walter Kidde Dinosaur Park, Riker Hill, New Jersey, in the upper Towaco Formation (Hettangiano, about 197 Myr) from the Newark basin (Olsen & Rainforth 2001). Numerous vertebrate tracks were collected from a second locality in the Early Jurassic upper Elliot Formation, of the Stormberg Group of the Karoo basin of South Africa (Ellenberger 1970). Several specimens from this locality were originally assigned to a different ichnogenus, considered herein as junior synonyms of Ameghinichnus (= Eopentapodicus). The third locality corresponds to the early Hettangiano Zagaje Formation from Sołtyków, Poland (Gierliński et al. 2004), with a single track of Ameghinichnus.
All the localities are dated as Early Jurassic in age, so the specimens are at least 25 Myr older than those from the La Matilde Formation (Callovian-Bajocian; late Middle Jurassic), extending back the record of the ichnogenus.
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Mammalian nature of tracks and paleobiology of the trackmaker “Mammals” are here considered sensu lato, not following a strict phylogenetic definition (e.g. Rougier
2002). The record of mammal tracks begins with few occurrences during the early Mesozoic Era, or even mammal-like specimens in Permian facies, and a remarkable increase in the number of records of mammalian ichnotaxa since the Early Cretaceous (e.g. Sarjeant & Langston 1994; Rainforth & Lockley 1996; Sarjeant 2000; Lockley & Foster 2003; Abbassi & Lockley 2004).
After an analysis of the characteristics and morphologies of the purported primitive or basal mammal trackmakers, those suggested in this paper to distinguish mammal and mammal-like from non-mammal tracks, are: 1) an overall similarity to conservative mammal tracks; 2) pentadactyl manus and pes (in general); 3) digit impressions subequal in size and shape; 4) mesaxonic tracks; 5) no sprawling gait; 6) advanced gait indicating important locomotion development (e.g. running, galloping or hopping gaits), related with 5); and 7) relatively small-sized tracks. The presence of pentadactyly in the imprints does not demonstrate by itself a mammalian origin because many tetrapod groups, apart from mammals, have pentadactyl feet and two pairs of limbs joined to two girdles (e.g. Ziswiler 1980; Kardong 1999). Therefore, it is necessary to observe the co-occurrence of several of the features mentioned above to be able to evaluate the type of trackmaker. Ideally, in order to study this combination of features, analysis must be based on a large sample size and the full variability of the footprint population must be considered.
However, the current bone fossil record of basal mammals is scarce and precludes a consensus amongst early mammalian researchers with regards the structure of the limbs of the first true mammals and their ancestor group, the therapsids. Therefore, an increased knowledge of the fossil record is needed to define more precisely the anatomy of the taxonomical groups involved.
On the basis of the characteristics suggested as distinctive of mammal tracks and existing evidences, the assignment of Ameghinichnus to Mammalia Linnaeus, 1758 is supported here, an opinion shared by several other authors (e.g. Casamiquela 1961, 1964, 1974; Bonaparte 1978; Rainforth & Lockley 1996; Kielan-Jaworowska et al. 2004). Nevertheless, it is important to mention that some authors consider that such tracks could have been made by a different of group of vertebrates, such as advanced therapsids (Olsen & Galton 1984; Olsen et al. 1992; Olsen & Rainforth 2001).
With regard to the opinion of a mammalian origin, there is insufficient information available to determine the taxonomic group inside Mammalia to which Ameghinichnus is related. Casamiquela (1961, 1964) assigned Ameghinichnus to the marsupials or the “pantotheres”. Later, the same author (Casamiquela 1974: 77) suggested that the tracks should be assigned to the primitive Theria, Holotheria (Patriotheria) or again “pantotheres”. Bonaparte (1978) claimed that there was not enough postcranial data to assign the trackmaker to a particular group inside Mammalia. Later, on the basis of the inferred galloping gait, it was suggested a possible origin within the multituberculates (Kielan-Jaworowska & Gambaryan 1994; Kielan-Jaworowska et al. 2004; Bonaparte, pers. comm. in Gurovich 2006). Leonardi (1994) referred them as holotheres with reservations, although Sarjeant (2000) questioned this assignment because for the presence of the tail mark.
Recently, some bone fossils from the Jurassic Cañadón Asfalto Formation, in Chubut province, Argentina, have been assigned to different groups of Mammalia (Rauhut et al. 2002; Forasiepi et al. 2004; Martin & Rauhut 2005; Gurovich 2006; Rougier et al. 2007 a,b; Gaetano & Rougier 2008). Among the bone fossils found, an appreciable amount of postcranial material assigned to the limbs is still unpublished (Rougier, G., com. pers. 2006; Gaetano & Rougier 2008).
The trackways of Ameghinichnus, or at least A. patagonicus, may display two different configurations, in both cases with the pes located externally and oversteping or slightly overlapping the manus. In the first one, the ipsilateral imprints are in an alternating arrangement, in some cases associated with a continuous and curved or sinuous tail mark (e.g. trackway 1 in Fig. 4b). In the second arrangement, both sets accounting for the four limbs of the trackmaker are in a group as transverse or opposite arrangement. In some cases, the four imprints are nearly transversely lined up (e.g. trackway 2 in Fig. 4b), but usually, the manus are located somewhat posterior to the pes, lined up transversely or with a slight displacement between each other relative to the direction of travel (e.g. Fig. 3e). This second arrangement can be associated with a discrete and straight
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tail mark, parallel or semi-parallel to the midline (e.g. trackway 2 in Fig. 4b). This is not the first mention of this kind of gait, the hopping gait, even with an associated tail mark having already been discussed in the literature (e.g. Brasilichnium Leonardi, 1981, from the Triassic Botucatú Formation; trackways assigned to rodent from the Miocene Browns Park Formation, Lockley et al. 2007).
Casamiquela (1964) related both dispositions with two kinds of gait: the first, a walking gait, and the second, a jumping or hopping gait with transition to a galloping gait (running to galloping gait after Leonardi 1987). They are distinguished by symmetric and asymmetric gaits, respectively (Grillner et al. 2000; Abourachid 2003).
The ability to gallop would have allowed the producer of Ameghinichnus to move at high speeds (Casamiquela 1974), and to escape predators efficiently (e.g. Sarmientichnus trackmaker, a likely running theropod; Casamiquela 1974; Melchor et al. 2004). The long tail would have allowed the producer of Ameghinichnus to reduce the instability of a galloping gait, giving a third point of support. This in turn enabled the gravitational centre to move towards a more stable position with regards to the triangle of support, similar to a tripod (Kardong 1999; Willey et al. 2004).
The size of the specimens of Ameghinichnus from the La Matilde Formation displays certain variability, considering the different size of the tracks of A. patagonicus, A. manantialensis and the other tracks assigned only at the ichnogenus level (MPM-PIc-3957). It is possible that this range might represent an artificial division of a continuous ontogenetic growth series, or different phylogenetically related taxa.
Conclusions
Agreements on common and simple ichnotaxonomic criteria are needed to facilitate communication between researchers and highlight the utility of trace fossils in paleoenviromental, paleoecological, behavioural, and census studies. These conventions are especially important for vertebrate ichnology, a field where the ichnotaxonomy of the tracks are frequently based on the age of footprint bearing rocks, supposed producer, and provincial names as the main ichnotaxobases.
The application of the proposed ichnotaxobases to the mammal ichnofauna from the Middle Jurassic La Matilde Formation resulted in the recognition of two ichnospecies of Ameghinichnus and a potentially different track. The most abundant tracks were assigned to Ameghinichnus patagonicus Casamiquela, 1961. At the same time, a set of similar tracks (previously subsumed as A. patagonicus) are assigned to a new ichnospecies, Ameghinichnus manantialensis. The characteristics of the imprints indicate a mammal affinity, but the scarcity of available postcranial skeletal material for Jurassic mammals precludes a phylogenetical identification to a taxon within Mammalia as the possible trackmaker of Ameghinichnus.
Mammal body fossils are scarce in the Jurassic of Gondwana, particularly in South America. Consequently the presence of these tracks provides important evidence of the evolution and diversity of the mammals.
Acknowledgments
This research was funded by a grant from The Jurassic Foundation. I thank F. González and F. Giménez for their assistance during the field trips in Santa Cruz Province, and technical staff of the Museo Paleontológico Egidio Feruglio for the preparation of part of the specimens. The comments by J. Genise and R. Melchor on early drafts of the manuscript have been much appreciated. I am grateful to the following museum curators for providing access to their collections: A. Kramarz (Museo Argentino de Ciencias Naturales Bernardino Rivadavia, Buenos Aires), J. Powel (Instituto Miguel Lillo, Tucumán), S. Bargo and M. Reguero (Museo de La Plata, Buenos Aires), E. Ruigomez (Museo Paleontológico Egidio Feruglio, Chubut), A. Dondas (Museo de Ciencias Naturales Lorenzo Scaglia, Buenos Aires), and M. Palacios (Museo Regional Provincial Padre
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Manuel Jesús Molina, Santa Cruz). I am indebted to the Secretaria de Cultura of Santa Cruz province (Argentina) for permissions to work in the area. I am especially grateful to Mr. Naves, owner of the farm, for his kind help and company. E. Rainforth shared photographs of the Ellenberger collection (Montpellier) of tracks from South Africa, and R. Melchor shared photographs of some specimens from the La Matilde Formation. Y. Gurovich, N. Parker and E. Manning helped with the English redaction. M. Lockley, G. Rougier and P. Gaubert made valuable comments that greatly improved the manuscript.
References
Abbassi, N. & Lockley, M.G. (2004) Eocene bird and mammal tracks from the Karaj Formation, Tarom Mountains, Northwestern Iran. Ichnos, 11, 349–356.
Abourachid, A. (2003) A new way of analysing symmetrical and asymmetrical gaits in quadrupeds. Comptes Rendus Biologies, 326, 625–630.
Andreis, R.R., Cúneo, R. & Zalba, P.E. (1992) Patagonia Field Trip Guide. 4 Reunión Argentina de Sedimentología. Museo Paleontológico Egidio Feruglio, 37 pp.
Bertling, M., Braddy, S., Bromley, R.G., Demathieu, G.R., Genise, J., Mikuláš, R., Nielsen, J.K., Nielsen, K.S.S., Rindsberg, A.K., Schlirf, M. & Uchman, A. (2006) Names for trace fossils: a uniform approach. Lethaia, 39, 265–286.
Bonaparte, J.F. (1978) El Mesozoico de América del Sur y sus tetrápodos. Fundación Miguel Lillo, Opera Lilloana, 26, Tucumán, 596 pp.
Bonaparte, J.F. (1983) Jurassic tetrapods from South America and dispersal routes. In: Jacobs, L.L. (Ed.), Aspects of vertebrate history: Essay in honor of Edwin Harris Colbert. Museum of Northern Arizona Press, pp. 73–98.
Bromley, R.G. (1990) Trace fossils: Biology and Taphonomy. Special Topics in Paleontology 3, Unwin Hyman, London, 310 pp.
Casamiquela, R.M. (1960) El hallazgo del primer elenco (icnológico) jurásico de vertebrados terrestres de Latinoamérica (noticia). Revista de la Asociación Geológica Argentina, 15, 5–14.
Casamiquela, R.M. (1961) Sobre la presencia de un mamífero en el primer elenco (icnológico) de vertebrados del Jurásico de la Patagonia. Physis, 22, 225–233.
Casamiquela, R.M. (1964) Estudios icnológicos. Problemas y métodos de la icnología con aplicación al estudio de pisadas mesozoicas (Reptilia, Mammalia) de la Patagonia. Colegio Industrial Pío IX, Buenos Aires, Argentina, 229 pp.
Casamiquela, R.M. (1974) Sobre la significación de Ameghinichnus patagonicus, un mamífero brincador del Jurásico Medio de Santa Cruz (Patagonia). Actas I Congreso Argentino de Paleontología y Bioestratigrafía, Tucumán, II, 1974, pp. 71–85.
Casamiquela, R.M. (2002) Icnitas de vertebrados (Mamíferos, Dinosaurios) del Mesojurásico. In: Haller, M.J. (Ed.), Geología y Recursos Naturales de Santa Cruz, Relatorio del 15 Congreso Geológico Argentino, II, pp. 433–438.
Cladera, G., Andreis, R., Archangelsky, S. & Cúneo, R. (2002) Estratigrafía del Grupo Baqueró, Patagonia (provincia de Santa Cruz, Argentina). Ameghiniana, 39, 3–20.
Coria, R.A. (1989) Primer registro icnológico de dinosaurio en el Jurásico Medio de la Argentina. Abstracts 6 Jornadas Argentinas de Paleontología de Vertebrados, San Juan, 1989, pp. 107–108.
Coria, R.A. & Paulina Carabajal, A. (2004) Nuevas huellas de Theropoda (Dinosauria: Saurischia) del Jurásico de Patagonia, Argentina. Ameghiniana, 41, 393–398.
De Barrio, R.E., Panza, J.L. & Nullo, F.E. (1999) Jurásico y Cretácico del Macizo del Deseado, provincia de Santa Cruz. In: Caminos, R. (Ed.), Geología Argentina. Anales Instituto de Geología y Recursos Naturales, 29, SEGEMAR, Buenos Aires, pp. 511–527.
De Valais, S. (2008) Icnología de tetrápodos Triásicos y Jurásicos de Argentina: aportes al origen de las aves y los mamíferos. Unpublished PhD thesis, Universidad de Buenos Aires, Buenos Aires, Argentina, 316 pp.
De Valais, S. & Melchor, R.N. (2003) Nuevos aportes sobre la icnofauna de la Formación La Matilde (Jurásico Medio), provincia de Santa Cruz, Argentina. Ameghiniana, 40 (Supplement), 53R–54R.
De Valais, S. & Melchor, R.N. (2008) Ichnotaxonomy of bird-like footprints: an example from the Late Triassic-Early Jurassic of Northwest Argentina. Journal of Vertebrate Paleontology, 28, 145–159.
De Valais, S., Melchor, R.N. & Genise, J.F. (2003) Hexapodichnus casamiquelai, isp. nov.: an arthropod trackway from the La Matilde Formation (Middle Jurassic), Santa Cruz, Argentina. Asociación Paleontológica Argentina, Publicación Especial, 9, 35–41.
Ellenberger, P. (1970) Les niveaux paleontologiques de premiere apparition des mammiferes primordiaux en Afrique du Sud et leur ichnologie. Establissement de zones stratigraphiques detaillees dans le Stormberg du Lesotho (Afrique
TERMS OF USEThis pdf is provided by Magnolia Press for private/research use. Commercial sale or deposition in a public library or website is prohibited.
du Sud) (Trias superieur a Jurassique). Abstracts 2 Gondwana Symposium, South Africa, 1970, pp. 343–370.Ellenberger, P. (1972) Contribution à la classification des pistes de vertébrés du Trias: les types du Stomberg d´Afrique
du Sud (I). Palaeovertebrata, Memoire Extraordinaire, Montpellier, 134 pp.Ellenberger, P. (1974) Contribution à la classification des pistes de vertébrés du Trias: les types du Stomberg d´Afrique
du Sud (II). Palaeovertebrata, Memoire Extraordinaire, Montpellier, 142 pp.Ellenberger, P. (1975) L´explosion démographique des petits quadrupèdes a allure de mammifères dans le Stormberg
supérieur (Trias) d´Afrique du sud aperçu sur leur origine au Permien (France et Karoo). Colloque international cu centre National de la Recherche Scientifique, 218. Problèmes actuaels de Paléontologie (Évolution des vertébrés), pp. 409–439.
Forasiepi, A.M., Rougier, G.W. & Martinelli, A. (2004) A new mammal from the Jurassic Cañadón Asfalto Formation, Chubut Province (Argentina). Journal of Vertebrate Paleontology, 24 (Supplement 3), 59A.
Gaetano, L.C. & Rougier, G.W. (2008) The Middle Jurassic triconodont Argentoconodon fariasorum: phylogeny and biogeography. Abstract 3 Congreso Latinoamericano de Paleontología de Vertebrados, Neuquen, 2008, p. 105.
Gierliński, G., Pienkowski, G. & Niedźwiedzki, G. (2004) Tetrapod track assemblage in the Hettangian of Sołtyków, Poland, and its paleoenvironmental background. Ichnos, 11, 195–213.
Gierliński, G., Niedwiedzki, G. & Pienkowski, G. (2005) Early Hettangian vertebrate ichnoassemblage from Poland. Abstracts of Tracking dinosaur origins. The Triassic/Jurassic terretrial transition, Conference, Utah, 3–4.
Gradstein, F.M. & Ogg, J.G. (2004) Geologic time scale 2004. Why, how, and where next! Lethaia, 37, 175–181.Grillner, S., Cangiano, L., Hu, G-Y., Thompson, R., Hill, R. & Wallén, P. (2000) The intrinsic function of a motor system
- from ion channels to networks and behavior. Brain Research, 886, 224–236.Gurovich, Y. (2006) Bio-Evolutionary aspects of Mesozoic Mammals: Description phylogenetic relationships and
evolution of the Gondwanatheria (Late Cretaceous and Paleocene of Gondwana). Unpublished PhD Thesis, Universidad de Buenos Aires, Buenos Aires, Argentina, 574 pp.
Hitchcock, E. (1858) Ichnology of New England. A repost on the sandstone of the Connecticut Valley especially its fossil footmarks. Natural Sciences in America Reprint. Arno Press, Boston, 220 pp.
Ji, Q., Luo, Z-X., Yuan, Ch-X., Wible, J.R., Zhang, J-P. & Georgi, A.J. (2002) The earliest known eutherian mammal. Nature, 416, 816–822.
Kardong, K.V. (1999) Vertebrados. Anatomía comparada, función, evolución. 2 Edición. Mc Graw Hill-Interamericana, Madrid, 732 pp.
Kielan-Jaworowska, Z. & Gambaryan, P.P. (1994) Postcranial anatomy and habits of Asian multituberculate mammals. Fossils and Strata, 36, 1–92.
Kielan-Jaworowska, Z. & Hurum, J.H. (2006) Limb posture in early mammals: sprawling or parasagittal. Acta Palaeontologica Polonica, 51, 393–406.
Kielan-Jaworowska, Z., Cifelli, R.L. & Luo, Z-X. (2004) Mammals from the Age of Dinosaurs: Origins, Evolution, and Structure. Columbia University Press, New York, 620 pp.
Leonardi, G. (1981) Novo Icnogênero de tetrápode Mesozóico da Formação Botucatu, Araraquara, SP. Anais da Academia Brasileira de Ciencias, 53, 795–805.
Leonardi, G. (1987) Glossary and manual of tetrapod palaeoichnology. Departamento Nacional da Produção Mineral, Brasilia, Brasil, 115 pp.
Leonardi, G. (1994) Annotated atlas of South America tetrapod footprints (Devonian to Holocene). Companhia de Pesquisa de Recursos Minerais, Rio de Janeiro, Brasil, 247 pp.
Leonardi, G. & de Oliveira Lima, F.H. (1990) A revision of the Triassic and Jurassic tetrapod footprints of Argentina and a new approach on the age and meaning of the Botucatu Formation footprints (Brazil). Revista Brasileira de Geociências, 20, 216–229.
Lesta, P. & Ferello, R. (1972) Región extraandina de Chubut y norte de Santa Cruz. In: Leanza, H. (Ed.), Geología Regional Argentina. Academia Nacional Ciencias Córdoba, pp. 601–653.
Liliernstern, von, H.R. (1944) Eine Dicynodontierfährte aus dem Chirotheriumsandstein von Hessberg bei Hildburghausenr. Paläontologische Zeitschrift, 23, 368–385.
Linnaeus, C. (1758) Systema naturae per regna tria naturae, secundum classic, ordines, genera, species cum characteribus, differentiis, synonums locis. Editio decima, reformata. Laurentii Salvii, Stockholm, 1, 824 pp.
Lockley, M.G. & Foster, J.R. (2003) Late Cretaceous mammal tracks from North America. Ichnos, 10, 269–276.Lockley, M., Culver, T.S. & Wegweiser, M. (2007) An ichnofauna of hopping rodent and arthropod trackways from the
Miocene of Colorado. In: Lucas, S.G., Spielmann, J.A. & Lockley, M.G. (Eds.), Cenozoic vertebrate tracks and traces. New Mexico Museum of Natural History and Science Bulletin, 42, pp. 59–66.
Lockley, M.G., Lucas, S.G., Hunt, A.P. & Gaston, R. (2004) Ichnofaunas from the Triassic-Jurassic boundary sequences of the gateway area, Western Colorado: implications for faunal composition and correlations with other areas. Ichnos, 11, 89–102.
Martin, T. & Rauhut, O.W.M. (2005) Mandible and dentition of Asfaltomylos patagonicus (Australosphenida, Mammalia) and the Evolution of tribosphenic teeth. Journal of Vertebrate Paleontology, 25, 414–425.
TERMS OF USEThis pdf is provided by Magnolia Press for private/research use. Commercial sale or deposition in a public library or website is prohibited.
Mazzoni, M.M., Spalletti, L.A., Iñíguez Rodrígues, A.M. & Teruggi, M.E. (1981) El Grupo Bahía Laura en el Gran Bajo de San Julián. Provincia de Santa Cruz. Actas 8 Congreso Geológico Argentino, 1981, 3, 485–507.
McCrea, R.T., Pemberton, S.G. & Currie, P.J. (2004) New ichnotaxa of mammal and reptile tracks from the Upper Paleocene of Alberta. Ichnos, 11, 323–339.
Melchor, R.N. & de Valais, S. (2006) A review of Triassic tetrapod track assemblages from Argentina: a reassessment. Palaeontology, 49, 355–379.
Melchor, R.N., de Valais, S. & Genise, J.F. (2004) Middle Jurassic mammalian and dinosaur footprints and petrified forests from the volcaniclastic La Matilde Formation. In: Bellosi, E. S. & Melchor, R. N (Eds.), Fieldtrip guidebook. I International Congress on Ichnology, Museo Egidio Feruglio, Trelew, pp. 47–63.
Murie, O.J. (1974) Animal tracks. Peterson Field Guides. 2 Edición. Houghton Miffin Company, New York, 375 pp.Olsen, P.E. & Galton, P.M. (1984) A review of the reptile and amphibian assemblage from the Stormberg of Southern
Africa, with special emphasis on the footprints and the age of the Stormberg. Palaeontology African, 25, 87–110. Olsen, P.E. & Rainforth, E.C. (2001) The “Age of Dinosaurs” in the Newark Basin, with special reference to the Lower
Hudson Valley. New York State Geological Association Guidebook, pp. 59–176. Panza, J.L. (1998) Hoja geológica 4769-IV “Monumento Natural Bosques Petrificados”, escala 1:250.000, provincia de
Santa Cruz. Boletín del Servicio Geológico Minero Argentino, 257, Buenos Aires, pp. 1–118 (unpublished).Panza, J.L. & Genini, A. (1998) Hoja Geológica 4769-IV, Monumento Natural Bosques Petrificados, escala 1:250000,
provincia de Santa Cruz. Servicio Geológico Nacional, Buenos Aires, 163 pp.Panza, J.L. & Haller, M.L. (2002) El volcanismo jurásico. In: Haller, M.J. (Ed.), Geología y Recursos Naturales de Santa
Cruz. Relatorio 15º Congreso Geológico Argentino, 2002, I–7, Santa Cruz, pp. 89–101.Rainforth, E.C. & Lockley, M.G. (1996) Tracks of diminutive dinosaurs and hopping mammals from the Jurassic of
North and South America. In: Morales, M. (Ed.), The continental Jurassic. Museum of Northern Arizona Bulletin 60, pp. 265–269.
Rauhut, O.W.M., Martin, T., Ortiz-Jaureguizar, E. & Puerta, P. (2002) A Jurassic mammal from South America. Nature, 416, 165–168.
Rezendes, P. (1995) Tracking and the art of seeing. How to read animal tracks and sign. Camben House Publishing, Inc, Ontario, 320 pp.
Rougier, G.W. (2002) Mesozoic mammals. Encyclopedia of Life Sciences, 11, 562–567.Rougier, G.W., Martinelli, A.G., Forasiepi, A.M. & Novacek, M.J. (2007a) New Jurassic mammals from Patagonia,
Argentina: a reappraisal of australosphenidan morphology and interrelationships. American Museum Novitates, 3566, 1–54.
Rougier, G.W., Garrido, A., Gaetano, L., Puerta, P.F., Corbitt, C. & Novacek, M.J. (2007b) First Jurassic Triconodont from South America. American Museum Novitates, 3580, 1–17.
Sarjeant, W.A.S. (2000) The mesozoic mammal footprint record reconsidered: with an account of new discoveries in the Cretaceous of Northwestern Alberta, Canada. Paleontology Society of Korea Special Publication, 4, 153–168.
Sarjeant, W.A.S. & Langston, W., Jr. (1994) Vertebrate footprints and invertebrate traces from the Chadronian (Late Eocene) of Trans-Pecos Texas. Texas Memorial Museum Bulletin 36, 86 pp.
Scrivner, P.J. & Bottjer, D.J. (1986) Neogene avian and mammalian tracks from Death Valley National Monument, California: their context, classification and preservation. Palaeogeography, Palaeoclimatology, Palaeoecology, 57, 285–331.
Stipanicic, O. & Reig, A.O. (1956) Posiciones estratigráficas y edades de las principales floras jurásicas argentinas. II Floras doggerianas y málmicas. Ameghiniana, 7, 101–118.
Stipanicic, O. & Reig, A.O. (1956) El “Complejo Porfírico de la Patagonia extraandina” y su fauna de anuros. Acta Geológica Lilloana, 1, 185–297.
Thulborn, T. (1990) Dinosaurs tracks. Chapman and Hall, London, 409 pp.Trewin, N.H. (1994) A draft system for the identification and description of arthropod trackways. Palaeontology, 37,
811–823.Vialov, O.S. (1966) Sledy zhiznedeiatel´nosti organizmow i ikh paleontogicheskoe znachenie. Kiev: Naukova Dumka.
Academy of Sciences, Ukranian, 219 pp.Willey, J.S., Biknevicius, A.R., Reilly, S.M. & Earls, K.D. (2004) The tale of the tail: limb function and locomotor
mechanics in Alligator mississippiensis. The Journal of Experimental Biology, 207, 553–563.Ziswiler, V. (1980) Zoología especial. Vertebrados. Tomo II: Amniotas. Ediciones Omega, Barcelona, España, 411 pp.
