ESCAPA, I.H., J. STERLI, D. POL, & L. NICOLI. 2008. Jurassic

Revista de la Asociación Geológica Argentina 63 (4): 613 - 624 (2008) 613

JURASSIC TETRAPODS AND FLORA OF CAÑADÓN ASFALTO FORMATION IN CERRO CÓNDOR AREA, CHUBUT PROVINCE

Ignacio H. ESCAPA1, Juliana STERLI2, Diego POL1 and Laura NICOLI3

1 CONICET. Museo Paleontológico Egidio Feruglio. Trelew, Chubut. Email: [email protected], [email protected] 2 CONICET. Museo de Historia Natural de San Rafael, San Rafael, Mendoza. Email: [email protected] 3 CONICET. Departamento de Ciencias Geológicas, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires. Buenos Aires. Email: [email protected]

ABSTRACT The plant and tetrapod fossil record of the Cañadón Asfalto Formation (Middle to Late Jurassic) found in Cerro Cóndor area (Chubut Province) is summarized here. The flora is dominated by conifers (Araucariaceae, Cupressaceae sensu lato) but also includes ferns and equisetaleans. The tetrapod fauna is composed of dinosaur taxa described in the 70's as well as other remains recently described and other vertebrate groups such as amphibians, turtles, and mammals. The amphibian remains have been interpreted as representatives of a new species of Notobatrachus, considered one of the most basal members of the anuran lineage. Similarly, turtle remains have been recently recognized as a new species of basal turtle, bringing valuable infor- mation about the early evolution of this group. The dinosaur remains are largely dominated by saurischian taxa, represented by basal forms of Eusauropoda and Tetanurae. In addition, three different mammalian species have been identified and considered as early representatives of an endemic Gondwanan mammalian fauna. The fossil record of this formation represents the most completely known biota from the continental Middle to Late Jurassic of the Southern Hemisphere and one of the most complete of the entire world. Keywords: Jurassic, Patagonia, Paleobiogeography, Flora, Fauna.

RESUMEN: Flora y tetrápodos del Jurásico de la Formación Cañadón Asfalto en el área de Cerro Cóndor, provincia de Chubut. Se resume bre- vemente el registro de plantas y tetrápodos fósiles de la Formación Cañadón Asfalto (Jurásico Medio a Superior) en el área de Cerro Cóndor, provincia de Chubut. La flora está conformada por coníferas de las familias Araucariaceae y Cupressaceae sensu lato dominando la asociación, la cual se completa con helechos y equisetales en proporciones menores. La fauna de tetrápodos se compone por los clásicos dinosaurios descriptos en los 70`s, a los que se suman nuevos restos pertenecientes a este grupo, así como anfibios, tortugas y mamíferos coleccionados en la última década. Los restos de anfibios han sido inter- pretados como representantes de una nueva especie de Notobatrachus, considerado uno de los miembros más basales del lina- je de los anuros. De igual modo, los restos de tortugas han sido recientemente reconocidos como una nueva especie de tor- tuga basal la cual aporta valiosa información acerca de la evolución temprana de este grupo. Los restos de dinosaurios se encuentran mayormente dominados por saurisquios, representados por formas basales de Eusauropoda y Tetanurae. Asimismo, tres diferentes especies de mamíferos han sido identificadas y consideradas como representantes basales de una fauna de mamíferos endémica de Gondwana. El registro de las formas clásicas en conjunto con los grupos taxonómicos recientemente descriptos, representan la biota del Jurásico Medio a Superior continental más completa de Gondwana, y una de las más completas a nivel global.

Palabras clave: Jurásico, Patagonia, Paleobiogeografía, Flora, Fauna.

INTRODUCTION Silva Nieto et al. (2003) have identified vial system on the lacustrine previous de- two members in the Cañadón Asfalto posits (Cabaleri et al. 2005). Alternatively, The Jurassic Cañadón Asfalto Formation Formation: Las Chacritas in the lower some of the fluvial deposits traditionally crops out along the middle Chubut river section and Puesto Almada in the upper referred to the Cañadón Asfalto Forma- valley (Fig. 1). This unit transitionally portion of the unit. The lower member is tion have been considered a different overlies volcanic rocks of the Lonco Tra- mostly dominated by lacustrine sedi- unit: the Cañadón Calcáreo Formation pial Formation and is uncomformably ments with volcanic intercalations at the (Proserpio 1987, Figari and Courtade overimposed by the Cretaceous Chubut base, while the upper one is mainly silici- 1993). From a sequence stratigraphy Group (Page et al. 1999). clastic and it represents a prograding flu- viewpoint, Figari et al. (1996) interpreted 614 I.H. ESCAPA, J. STERLI, D. POL AND L. NICOLI

Figure 1: Geological map of the Cerro Cóndor area, Chubut Province. Modified from Silva Nieto et al. (2002). the Cañadón Asfalto basin as a rift deve- tion has been referred to the Middle to ceous age (Silva Nieto et al. 2007). loped from the Triassic through the late Upper Jurassic (Callovian-Oxfordian) ba- The aim of this work is to summarize re- Cretaceous. These authors recognized a sed on its paleontological content (Fren- cent advances in the knowledge of the series of four major megasequences, the guelli 1949a, Tasch and Volkheimer Cañadón Asfalto Formation paleobiota second one corresponding with the Ca- 1970, Volkheimer 1971, Silva Nieto et al. in the Cerro Cóndor area, Chubut pro- ñadón Asfalto Formation. More recently, 2007). However, its age interpretation, vince. During the last ten years an inten- Silva Nieto et al. (2007) suggested that the which is mostly based on the fossils reco- sive fieldwork has been conducted and Cañadón Asfalto basin could be formed vered around the type locality (Cerro numerous new fossil localities have been by several pull-apart depocenters which Cóndor area), could not be entirely accu- discovered. There, several new plant, are not strictly contemporary. According rate for the remaining localities. For ins- reptile, mammal and amphibian taxa we- to these authors, each one of the depo- tance, recent palynological records from re unearthed from lacustrine sediments. centers would constitute an isolated ba- the upper section of the Cañadón As- In this contribution we are mainly focu- sin with its own evolutionary history. falto Formation in the northern area of sing on fossil tetrapods and plants, In general, the Cañadón Asfalto Forma- Cerro Cóndor suggest an early Creta- although the record of fresh water inver- Jurassic tetrapods and flora of Cañadón Asfalto Formation ... 615

tebrates is also remarkable (Tasch and water invertebrates have been found as sheath. Volkheimer 1970, Silva Nieto et al. 2007). well. Ferns: The ferns are a minor component The new specimens from Cañadón As- at Frenguelli site, but they are represen- Flora falto Formation are mostly dominated by ted by at least two morphospecies (see conifer branches, seed and pollen cones also Frenguelli 1949a). The low represen- Jurassic floras in southern Argentina are and isolated seeds with minor amounts tation of Pteridophyta in this locality is mostly known from Neuquén and Santa of equisetaleans, ferns and possible seed probably related with taphonomic bias Cruz provinces, but not much has been ferns. The conifers represent about 90 more than with a real representation of accomplished from the Chubut province. percent of the specimens recovered whi- the original flora. Considering that this However plant bearing sequences in le all the remaining groups represent the plant assemblage is dominated by plant Chubut province are widely distributed, 10 percent remnant. The high number of parts with higher preservational potential including Early trough Late Jurassic de- specimens collected has allowed a de-tai- (e.g. conifers branches, cones, seeds), a posits. Jurassic lithoestratigraphic units led description of some taxa, specialy high degree of selection and allochtho- from Chubut province bearing plant as- conifers referred to Araucariaceae and nous conditions ruled plant burying de- semblages are: 1) Taquetrén Formation Cupressaceae sensu lato families. One of position. (Bonetti 1964, Herbst and Anzótegui the most relevant characteristics of the Most of fern remains are assignable to 1968, Escapa et al. 2008a), 2) Pampa de flora is the complete absence of Cyca- the genus Sphenopteris (Fig. 2f), a morpho- Agnia Group (Herbst 1966), 3) Lonco dophyta (Cycadales and Bennetittales) taxon used to characterize only vegetati- Trapial Formation (Cortés and Baldoni and Ginkgophyta, which are usually do- ve parts. It is interesting to note that so- 1984) and 4) Cañadón Asfalto Formation minant in Early Jurassic floras. The ano- me additional fern-like remains are pro- (Frenguelli 1949a and b, Cortés and Bal- malous absence of these plant groups bably related to pteridosperms (seed doni 1984). In this regard, there have during the Middle and Late Jurassic in ferns), a group that shows vegetative sys- been constant discussions about the pro- Cerro Cóndor, which is reverted from tems similar to true ferns. per denomination of all of these geolo- the Early Cretaceous, could probably be Araucariaceae: Conifers of this family are gical units (see Silva Nieto et al. 2003 and a response to certain broad environmen- represented in the Frenguelli site by citations therein) but no consensus has tal/paleoclimatic changes associated with numerous well preserved leafy twigs, been achieved yet. For this reason, in this the dynamics of paleoclimatic belts du- female cones (Fig. 2d), and isolated ovu- paper we follow the formational names ring the Jurassic (Rees et al. 2000). liferous complexes of at least two spe- such as were originally used in the des- Equisetales: Several specimens of Equise- cies, one of them previously reported as cription of these floras. tum-like (Equisetaceae) axis and foliage Araucarites cutchensis (Frenguelli 1949a). In particular the Middle to Late Jurassic have been recovered from the Frenguelli Even when ovuliferous complexes of Cañadón Asfalto taphoflora was initially site (Fig. 2e). The specimens collected are Araucariaceae show relatively high size reported by Frenguelli (1949a), who des- represented by articulate vegetative sho- variation within individual species (see cribed a few specimens collected by Dr. ots, with internodes bounded by foliar Harris 1979, Rees and Cleal 2004), it can- Miguel Flores from probable lacustrine whorls. The leaves show a basal sheath not explain the two principal morpholo- sediments at the Cañadón Asfalto locality and a distal free part always shorter than gies observed in our specimens. There- (15 kilometers southern Cerro Cóndor vi- the sheath. fore, the size range and morphology bet- llage). Eleven taxa, including ferns, seed Equisetalean remains of Jurassic-Creta- ween the Cañadón Asfalto Formation ferns and conifers were briefly mentio- ceous age have been normally referred to specimens do not correspond with two ned from this locality. In a later paper, the form-genus Equisetites, even though ontogenetic steps of the same species, Frenguelli (1949b) described in more de- not significant morphological differences since both present mature characters tail two species of the genus Palyssia (Co- distinguish it from the extant genus such as a prominent central seed and a niferophyta). However, the interpreta- Equisetum. The low number of differen- distal ligule (Fig. 2a). The presence of tions and systematic assignations that Fren- ces observed between them could have a Araucariaceae of at least two very dis- guelli made to these specimens have been taphonomic explanation more than a real tinctive sizes constitutes a common fea- highly questioned. In the same Cerro morphological base. Other equisetalean ture with other Mesozoic localities from Cóndor area, from a new locality named genus mentioned from some Jurassic lo- Argentina (e.g. Araucarites baqueroensis and "Frenguelli site", we collected and descri- calities is Neocalamites, which is more A. minumus, Archangelsky 1966). bed numerous compression-impression common for Triassic outcrops. Opposite The Araucariaceae family shows a Sou- plant specimens with preserved organic to our specimens, Neocalamites shows lea- thern Hemisphere distribution, but du- tissues. Along with plant remains frag- ves with a reduced or absent foliar sheath ring the Mesozoic it was present in both mentary vertebrate remains and fresh and linear leaves always longer than the Hemispheres (see Florin 1940, Stockey 616 I.H. ESCAPA, J. STERLI, D. POL AND L. NICOLI

Figure 2: Flora of Frenguelli site, cañadón Lahuinco, Cerro Cóndor area. a) Araucarites cutchensis ovuliferous complex (MEF-Pb 1794). Scale bar 0.5 cm b) Cupressaceae sensu lato ovuliferous cone (MEF-Pb 2463). Scale bar 1 cm. c) Cupressaceae sensu lato pollen cones organically attached to leafy twigs of Elatocladus sp (MEF-Pb 2429). Scale bar 1 cm. d) Araucaria sp. Ovuliferous cone organically attached to a branch of Brachyphyllum sp. (MEF-Pb 1647). Scale bar 1cm. e) Equisetum sp. Fragment of ribbed axis showing foliar whorls on nodes (MEF-Pb 2008). Scale bar 1 cm. f) Sphenopteris sp. (MEF-Pb 2015). Scale bar 0.5 cm g) Brachyphyllum sp. (MEF-Pb 1803). Scale bar 1cm. Jurassic tetrapods and flora of Cañadón Asfalto Formation ... 617

1982, 1994, Stockey and Ko 1986, Del lle 1913, Archangelsky 1963, Villar de three dinosaur taxa (Patagosaurus fariasi Fueyo and Archangelsky 2002 and refe- Seoane 1998, Llorens and Del Fueyo Bonaparte, Volkheimeria chubutensis Bona- rences therein), specially Araucaria (and 2003), represented by vegetative and re- parte, and Piatnitzkysaurus floresi Bona- associated morphogenera). Particularly in productive organs of Athrotaxis ungeri. parte). Subsequent field work conducted Patagonia, Araucariaceae played an im- Following this, the Middle Jurassic Cu- during the 80's by Bonaparte resulted in portant role in most Jurassic and Cre- pressaceae s.l. of Cañadón Asfalto For- a large number of dinosaur remains from taceous environments as indicated by its mation, together with another species re- this unit (most of which have been refe- wide distribution and abundance (see cently described (Escapa et al. 2008b), rred to P. fariasi). The known tetrapod Spegazzini 1924, Frenguelli 1949a, Cal- could represent the oldest record of the diversity from this unit has been signifi- der 1953, Stockey 1978). family for the Southern Hemisphere, and cantly increased in the last five years, In some particular cases, the ovuliferous one of the oldest at global level. mainly through the development of co- cones have been found organically atta- Other conifers: Some specimens bound ve- llaborative projects conducted by Dr. ched to leafy twigs. The general morpho- getative shoots that due their morpho- Oliver Rauhut, Dr. Guillermo Rougier, logy of the branches is comparable to logy cannot be assigned to any of the and the Museo Paleontológico Egidio Fe- some species of Brachyphyllum morphoge- mentioned families. The general mor- ruglio (Trelew). The results of these pro- nus. Cuneate leaves are arranged in a he- phology of these specimens is compara- jects have provided not only new dino- lix closely appressed to the shoot axis. ble with the morphogenera Pagiophyllum saur taxa but also new taxa from other Isolated vegetative shoots present occa- and Brachyphyllum (Fig. 2, g). However, taxonomic groups, including amphibians, sional branches that show an irregular without cuticular or reproductive charac- mammals, turtles, and pterosaurs. arrangement. ters it is not possible to relate these leafy Amphibians: Frog remains recently collec- Cupressaceae sensu lato: Conifers previously twigs with any natural group because so- ted from the Zitarroza site in the Ca- reported as Palyssia (Frenguelli 1949 a me species of this morphogenus have ñadón Bagual locality have been interpre- and b) have been recently included in Cu- been found in organic connection with ted as a new species of Notobatrachus, N. pressaceae sensu lato (= Taxodiaceae + reproductive structures of different coni- reigi Báez and Nicoli (2008). The holoty- Cupressaceae sensu stricto) since the new fer families (e.g., Araucariaceae, Cheiro- pe is represented by a single specimen specimens (Figs. 2b and c) show a com- lepidaceae). preserved as partially articulated cranial bination of reproductive-vegetative cha- (mandible, suspensorium and maxillary racters typical for the basal forms of this Tetrapod fauna arch remains) and postcranial impres- family (Escapa et al. 2008b). The seed sions. Additional cranial and postcranial cones are normally single and terminally The tetrapod record of the Cañadón As- disarticulated material, also referable to attached to distal branches. They show a falto Formation is the most diverse Ju- this species, has been found in sediments simple organization, represented by heli- rassic assemblage in South America. In of the Queso Rallado and Frenguelli lo- cally disposed bracts, which support particular, this unit contrasts with the calities. Notobatrachus reigi is a large-sized small, inverted ovules. The bracts are fragmentary remains recovered in other frog (Fig. 3) that shares with the type spe- rhomboidal in shape with an acute apex Jurassic units of Patagonia, including Ro- cies of the genus, N. degiustoi, not only its and a quite distinctive abaxial keel. On ca Blanca (Lower Jurassic), Cerro Carne- morphology and general proportions but the other hand, the pollen cones are ter- rero (Lower to Middle Jurassic), and Tor- also the presence of a parasphenoid with minally disposed in clusters. Vegetative dillo (Upper Jurassic) formations. The a trifid cultriform process, a long maxilla organs are organized in two orders of only possible exception is the Cañadón with a dorsally directed pars palatina, branching that are covered by helically Calcáreo Formation where well preser- amphicoelous presacral vertebrae, free inserted univein leaves, dorsiventrally ved remains of three dinosaur taxa have ribs associated with robust transverse flattened with a decurrent insertion and a been recently found (Rich et al. 1999, processes, cleithrum medially expanded, distal free part, mostly diverging from the Rauhut et al. 2005, Rauhut 2006), al- radioulna lacking a well-developed ole- axis in one plane producing a distichous though some authors have recently sug- cranon process, a discrete intermedium appearance. Leafy twigs of this morpho- gested that the age of this unit is Lower in the carpus, and unfused tibiale and fi- logy, when are found isolated, are nor- Cretaceous rather than Upper Jurassic bulare. However, a maxilla with a distinct mally included into the morphogenus (Silva Nieto et al. 2007). pterygoid process and lacking teeth at Elatocladus. The first tetrapod record of the Cañadón least along the posterior two-thirds of its It is interesting to note that the oldest Asfalto Formation was published by Bo- length) and a complete maxillary arch record of Cuppressaceae s.l. in the Sou- naparte (1979) who discovered a sauro- distinguish this species from N. degiustoi. thern Hemisphere is dated back to the pod bone-bed in the vicinities of Cerro Living toads and frogs conform a well- late Early Cretaceous of Argentina (Ha- Cóndor village, from which he described corroborated monophyletic assemblage 618 I.H. ESCAPA, J. STERLI, D. POL AND L. NICOLI

named Anura (Frost et al. 2006). Notoba- America. Only two species, considered Turtles: Turtle remains, represented by trachus posses many but not all of the the most basal known salientian (Ford cranial and postcranial elements have be- derived features that characterize this as- and Cannatella 1993, Báez and Basso en found in Queso Rallado locality (Fig. semblage, thus, although its relationships 1996, Gao and Wang 2001) have been 4). These remains were identified as a have been discussed, it has been always recovered from Triassic sediments: Tria- new species named Condorchelys antiqua by considered one of the most basal mem- dobatrachus massinoti, represented by a sin- Sterli (2008). The peculiar mixture of bers of the anuran lineage (Stipanicic and gle, incomplete, partially articulated spe- plesiomorphic (such as the presence of Reig 1957, Casamiquela 1961, Hecht cimen from the Lower Triassic of Ma- an open interpterygoid vacuity, a primiti- < 1962, Griffiths 1963, Estes and Reig dagascar (Piveteau 1937, Estes and< Reig ve basicranium, broad vertebral scutes in 1973, Báez and Basso 1996,< Rocek 2000, 1973, Rage and Rocek 1989, Rocek and the carapace, among others) and derived Gao and Wang 2001, Gao and Chen Rage 2000), and Czatkobatrachus polonicus, characters (such as the morphology of 2004). In the last years, the inclusion of known from disarticulated bones of the the tympanic cavity, the absence of teeth, Notobatrachus in several phylogenetic Early Triassic fissure deposits at the among others) found in this turtle sug- analyses has corroborated its basal posi- Czatkowice locality in Poland (Evans and gests that C. antiqua does not belong to tion, which is even basal to the common Borsuk-Bialynicka 1998, Borsuk-Bialy- any of the modern turtle groups, but it ancestor of all extant species (Báez and nicka and Evans 2002). The Jurassic fos- represents an earlier stage in turtle evolu- Basso 1996, Gao and Wang 2001, Gao sil frogs collected outside South America tion (Sterli 2008). This result agrees with and Chen 2004). Consequently, this are not significantly more abundant: Rha- the hypothesis proposed by Joyce (2007) Jurassic frog is not contained in Anura dinosteous parvus from Late Jurassic Mo- about turtle evolution where some fossil but in Salientia, the more inclusive taxon rrison Formation of Utah (Henrici 1998) turtles had differentiated before the split that encloses Anura and all amphibians and Prosalirus bitis from the Early Jurassic of modern turtles into the two main ex- more closely related to anurans than to Kayenta Formation of Arizona (Shubin tant groups (Cryptodira and Pleurodira). salamanders. and Jenkins 1995, Jenkins and Shubin The new data brought by this new spe- It is interesting to note that, even when 1998), both only known by fragmentary, cies from Cerro Cóndor, together with the Triassic and Jurassic fossil record of disarticulated material, and Eodiscoglossus the results obtained by Joyce (2007) and salientians is scarce and fragmentary, No- santojae, from the Late Bathonian of Sterli and Joyce (2007), shed new eviden- tobatrachus is especially well preserved. Spain, represented by several specimens ce to understand the early history of this The type species, Notobatrachus degiustoi is partially articulated (Hecht 1970, Estes clade and, consequently, the origin of superbly preserved as numerous, fine and Reig 1973, Evans et al. 1990, Sanchiz modern turtle groups. The oldest almost impressions of disarticulated and par- 1998). Most of these Mesozoic species complete turtle remains were found in tially articulated skeletons, even at diffe- already posses the derived, particular the Upper Triassic of Germany and Ar- rent ontogenetic stages (Estes and Reig anatomy that characterize anuran and, gentina, however isolated fragments of 1973, Báez and Basso 1996, Báez and Ni- thus, they do not contribute significantly turtles were found in other localities in coli 2004). All the specimens of N. degius- to our understanding of the sequence of Thailand and Greenland (Baur 1887, Fra- toi have been recorded in many outcrops acquisitions that conduce to that particu- as 1913, Broin 1985, Jenkins et al. 1994, of the La Matilde Formation of the De- lar Bauplan or of the processes that un- Rougier et al. 1995). All these discoveries seado Massif area in the Santa Cruz pro- derlie its evolution. In summary, al- around the world during the Upper vince. Notoriously, the single other spe- though recent studies based on DNA se- Triassic show that turtles were well-spre- cies known from pre-Cretaceous sequen- quences of living amphibian have sug- ad by that time and that they should have ces in South America until now, Vieraella gested that the origin of Anura should originated before. During the Lower Ju- herbsti, also comes from southern Pata- have occurred in the Triassic (Roelants rassic the fossil turtle record is sparse and gonia, particularly the Early Jurassic Roca and Bossuyt 2005, Roelant et al. 2007), or only three species were described. The Blanca Formation of Santa Cruz. This even earlier (San Mauro et al. 2005), the most complete of these findings is Ka- species, however, is represented by only fossil record of this lineage is still defi- yentachelys aprix (North America) repre- one specimen, preserved as incomplete, cient. In this context, the presence of a sented by cranial and postcranial remains partially articulated ventral and dorsal relatively well-preserved basal salientia in (Gaffney et al. 1987). The other two Lo- impressions (Reig 1961, Estes and Reig the Cañadón Asfalto Formation not only wer Jurassic turtles are not so complete: 1973, Báez and Basso 1996). Few other contributes to our knowledge of the one is represented only by an isolated remains, either ascribed to the crown- early evolutionary history of the anuran, skull that was assigned to Australochelys group Anura or considered as outside the but also invites us to continue working in africanus (South Africa) and the other fin- anuran node, have been described from this sequence considering the potentiality ding is represented only by a carapace Triassic and Jurassic rocks outside South of its content of fossil frogs. and a plastron assigned to Indochelys spatu- Jurassic tetrapods and flora of Cañadón Asfalto Formation ... 619

Figure 3: Skeletal reconstruction of Notobatrachus reigi from the Cañadón Asfalto Formation at Cerro Cóndor, based on the reconstruction of N. degiustoi (Báez and Nicoli, 2004). a) Skeleton in dorsal aspect, pectoral girdle and hyobranchial skeleton not shown. b) Skull in ventral aspect. References: in grey, bones attributed to N. reigi (catalogued as MPEF-PV 3006, 3045, 3051, and 3181), in white, unknown elements.

Figure 4: Turtle remains found in the Cañadón Asfalto Formation at Cerro Cóndor (Queso Rallado locality) and shown in the reconstruction of the closely related turtle Kayentachelys aprix from the Lower Jurassic of Kayenta Formation, USA (modified from Gaffney et al. 1987). a) Dorsal view of the skull and carapace. b) Ventral view of the skull and carapace. References: in grey, turtle remains found in Queso Rallado Locality (based on MPEF-PV 1152 -holotype-, MPEF-PV 1783A, B and C, MPEF-PV 3131, MPEF-PV 3132, MPEF-PV 3134, MPEF-PV 3136, MPEF-PV 3147, and MPEF-PV 3160), in white, unknown elements. 620 I.H. ESCAPA, J. STERLI, D. POL AND L. NICOLI

gentoconodon fariasorum (Rougier et al 2007 b) is only known, until now, from an isolated molariform that possesses a combination of plesiomorphic and derived features. This molar is characterized by a distinctly crown dominated by a longitu- dinal series of three major cups, a morphology traditionally described as a triconodont molariform. Triconodont teeth are common during the Jurassic in the Laurasian landmasses and occur in several mammalian groups (e.g. Morganuco- dontidae, Amphilestidae, Triconodonti- dae, etc.), having apparently appeared independently in each lineage, and, thus, its presence is not useful to establish phylogenetic relationships and taxonomic as- signments (Rougier et al. 2007b). This, together with the fragmentary condition of Argentoconodon only allowed Rougier et al. Figure 5:. Skeletal reconstructions: a) Piatnitzkysaurus floresi (based on PVL 4073 and MACN-PV (2007b) to attribute this species to the CH895) and b) Patagoasurus fariasi (based on PVL 4170, PVL 4076, MACN-PV CH932, MACN-PV Theriimorpha clade. CH933, MACN-PV CH935, MACN-PV CH936) from the Cañadón Asfalto Formation the Cañadón Asfalto Formation at Cerro Cóndor. References: in grey, elements known from the holotype or refe- The other two recently discovered and rred specimens, in white, unknown elements. described mammalian species of Caña- dón Asfalto Formation are Asfaltomylos lata (India) (Gaffney and Kitching 1994, differentiation of the crown-group tur- patagonicus (Rauhut et al. 2002, Martin and Datta et al. 2000). During the Middle tles (Joyce 2007). Following the first hy- Rauhut 2005) and Henosferus molus (Rou- Jurassic the turtle record continues being pothesis, the crown-group turtles should gier et al. 2007a). Both share a derived tri- scarce and fragmentary and only few spe- have originated as soon as the oldest bosphenic molar pattern associated with cies from Russia, Thailand, China and known turtle appeared during the Upper plesiomorphic mandibular features (like Mongolia were described (Tong et al. Triassic. However, following the second the presence of a mandibular trough that 2002, Matzke et al. 2004, Sukhanov hypothesis, the turtle crown should have could be related with the presence of 2006). Fortunately, from the Upper appeared during the Middle to Late Ju- postdentary bones partially attached to Jurassic to the present, the fossil turtle rassic. As both hypotheses differ in a ti- the lower jaw). These taxa have been in- record is more abundant, and it shows me span of 60 million years approxima- terpreted as sister taxa, integrating the that during the Upper Jurassic turtles tely (between Upper Triassic and Middle family Henosferidae (Rougier et al. 2007 spread over other environments like la- Jurassic), all the findings belonging to a). Henosferidae represents a basal mem- goons and open seas. Condorchelys antiqua that period of time are very important to ber of Australosphenida, an assemblage represents the oldest continental turtle understand basal turtle relationships and of Gondwanan mammals that probably from the Jurassic of South America. Re- the origin and diversification of living also includes Monotremata (Luo et al. garding the tempo and mode in the di- turtles. It is in this context where Condor- 2002, Rauhut et al. 2002, Martin and versification of living turtle groups, there cheys antiqua from the Middle to Upper Rauhut 2005, Rougier et al. 2007a). The are two main hypotheses. Some authors Jurassic Cañadón Asfalto Formation be- presence of a tribosphenic molar pattern believe that all living and fossil turtles comes an important fossil in turtle evolu- in this group suggests that this pattern (with the exception of some fossil tur- tion. had evolved independently in two dis- tles) belong to some of the two clades of Mammals: Several mammalian specimens tinct mammal lineages, the Gondwanan living turtles, Pleurodira or Cryptodira (Mammalia sensu Luo et al. 2002), which Australosphenida and the Laurasian as- (Gaffney et al. 2007). On the contrary, represent at least three species of two di- semblage named Boreosphenida (Luo et other authors pointed out that many fos- fferent mammalian groups, have been real. 2002). It is interesting to note that the sil turtles do not belong to any of the covered from the Queso Rallado Locality other single Jurassic Australosphenida living turtle clades, instead of that, they (Rauhut et al. 2002, Rougier et al. 2007a, and also the oldest known representative would have originated previously to the b). Among them, the recently erected Ar- of the group, Ambondro mahbo, has been Jurassic tetrapods and flora of Cañadón Asfalto Formation ... 621

recovered from Bathonian sediments of semble the condition of Lapparentosaurus, reinforces the hypothesis of a Middle the Mahajanga Basin of Madagascar another fragmentary taxon known from Jurassic dinosaur fauna of pangeic distri- (Flynn et al. 1999), suggesting an extensi- the Middle Jurassic of Madagascar (Bo- bution. ve spread of this group in Gondwana naparte 1999). Although more remains during Middle Jurassic times (Rauhut et of this form are needed, Volkheimeria CONCLUSIONS al. 2002). seems to represent a very early stage in The similarities of Argentoconodon fariaso- the evolution of Sauropoda. Patagosaurus, The fossil record of Cañadón Asfalto rum with other taxa distributed in Lau- instead, is known from a large number of Formation represents the most complete rasia, in addition to the combination of remains (Bonaparte 1986, see also Coria taxonomic sampling of the continental plesiomorphic and derived features 1994 and Rauhut 2003) and constitutes Middle Late Jurassic of Gondwana, and found in this taxon and also in Asfalto- the best known basal eusauropod form one of the most complete at global level. mylos patagonicus and Henosferus molus, allo- the Southern Hemisphere. Basal eusau- In addition to the classic dinosaur biota wed Rougier et al. (2007b) to consider ropods dominated the herbivorous fauna described in the 70`s, new taxonomic them as early representatives of an ende- in the Middle Jurassic assemblages of groups are now represented as a result of mic Gondwanan mammal fauna not yet other regions (e.g. Europe, Russia, China) ten years of field works in Cerro Cóndor fully differentiated from the Laurasian and form the ancestral stock that gave area. New represented taxa include equi- forms during the Middle to Upper origin to Neosauropoda (the group the setaleans, ferns and conifers among Jurassic. In summary, these findings, con- later diversified and dominated the sau- plants and amphibians, turtles, dinosaurs, sidering their age and putative phyloge- ropod fossil record from the Late Juras- and mammals, among tetrapods. netic relationships, have provided inva- sic to the Late Cretaceous). Patagosaurus The known tetrapod taxa from the Ca- luable new evidence about the early evo- fariasi has been traditionally compared ñadón Asfalto Formation include mem- lution of mammals. with other Jurassic taxa from India (Ba- bers of groups with a worldwide distri- Dinosaurs: Two major groups of dino- rapasaurus), China (Shunosaurus, Omeisau- bution, denoting the lack of faunal diffe- saurs have been so far described from the rus), all of which form the set of basal rentiation between the southern and nor- Cañadón Asfalto Formation: Sauropoda eusauropods in recent phylogenetic ana- thern hemisphere by the Middle-Late and Theropoda. lyses (Upchurch 1998, Wilson 2002). Jurassic. The only exception to this pat- Sauropod dinosaurs constituted the ma- These forms, however, do not form a tern is the presence of australosphenids, jor component of the herbivorous fauna natural taxonomic group but rather re- a clade of small mammals only known given their abundance in this formation, present a set of different stages of the from the Southern Hemisphere. The fau- as also occur in most Jurassic and Creta- early evolutionary history of Eusauro- nal assemblage from the Cañadón As- ceous faunal assemblages of the Sou- poda. The worldwide distribution of all falto Formation is relevant not only from thern Hemisphere. The sauropod fossil these primitive forms shows that, so far, a biogeographical point of view but also record of the Cañadón Asfalto Forma- there is no evidence of regional differen- because they represent early members of tion is particularly important for unders- ces during the radiation of eusauropod the major Mesozoic radiation of their tanding the evolution of this group. The dinosaurs during the Middle Jurassic. respective groups (e.g. sauropods, thero- diversification of the major sauropods li- Theropods are the only carnivorous pods, turtles, anurans). These taxa thus neages occurred in the Jurassic, including group of Dinosauria and have a broad shed light on several evolutionary pro- the appearance of forms with body sizes fossil record from the Late Triassic. Two blems that were classically based on evi- exceeding those of any other terrestrial taxa are known from the Cañadón As- dence from the Northern Hemisphere. organism (an evolutionary trend that falto Formation: Piatnitzkysaurus floresi An interdisciplinary approach to these continued during the Cretaceous). Two (Bonaparte 1979) (Fig. 5a) and Condorrap- forms, as well as the analysis of the pale- sauropod taxa have been described by tor currumili (Rauhut 2005). As in the case obiogeographic and biostratigraphic sig- Bonaparte (1979), Volkheimeria chubutensis of the above mentioned sauropods, these nificance of these records, will provide and Patagosaurus fariasi (Fig. 5b), although taxa also form part of a primitive stock an integrative and supported reconstruc- Rauhut (2003) noted the possible presen- of theropods known as basal Tenta- tion of this Patagonian environment and ce of a third sauropod taxon among the nurans. Although Piatnitzkysaurus and its worldwide significance for un-ders- specimens referred to Patagosaurus. The Condorraptor may have been very closely tanding the evolution of the Jurassic former is only known from a series of related forms (Smith et al. 2007), they continental biota. presacral vertebrae, pelvic, and hindlimb form along with other basal tetanuran remains. The dorsal vertebrae show a se- theropods a worldwide distributed ACKNOWLEDGMENTS ries of plesiomorphic (primitive) charac- assemblage of taxa in recent phylogene- ters (Bonaparte 1999), some of which re- tic analyses (Smith et al. 2007), which The authors thank Ana María Zavattieri, 622 I.H. ESCAPA, J. STERLI, D. POL AND L. NICOLI

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