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First record of stereospondyls (Tetrapoda, Temnospondyli) in the Upper Triassic of Southern Brazil
Gondwana Research 15 (2009) 131–136
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GR Letter
First record of stereospondyls (Tetrapoda, Temnospondyli) in the Upper Triassic of Southern Brazil Sérgio Dias-da-Silva a,⁎, Eliseu Vieira Dias b, Cesar Leandro Schultz c a
Centro de Ciências Rurais, Universidade Federal do Pampa, Campus de São Gabriel, Avenida Antônio Trilha, 1847, Bairro Centro, CEP 97.300-000, São Gabriel, Rio Grande do Sul, Brasil Centro Universitário Positivo, Núcleo de Ciências Biológicas e da Saúde, Rua Prof. Pedro Viriato Parigot de Souza, 5.300, CEP 81.280-330, Curitiba, Paraná, Brasil Laboratório de Paleovertebrados, Departamento de Paleontologia e Estratigrafia, Instituto de Geociências, Universidade Federal do Rio Grande do Sul, Avenida Bento Gonçalves, 9.500 prédio 43.127/110 B, CEP: 91.540-000, Porto Alegre, Rio Grande do Sul, Brazil
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Article history: Received 21 October 2007 Received in revised form 16 July 2008 Accepted 16 July 2008 Available online 24 July 2008 Keywords: Temnospondyli Western Gondwana Paleobiogeography Rosário do Sul Group Santa Maria Supersequence
a b s t r a c t Stereospondyls survived the Permo-Triassic extinctions in a refuge probably located in the landmass that nowadays comprises Australia. Subsequently, they radiated to other parts of Pangaea, reaching their highest distribution and diversification during the Early Triassic. An incomplete interclavicle from the Caturrita Formation represents their first record in the Upper Triassic of Brazil. Previously, Upper Triassic South American stereospondyls were restricted to Argentina. This new record reinforces a former hypothesis that suggests the presence of a more diverse stereospondyl fauna in South America during the Late Triassic than previously assumed. Additionally, the presence of a stereospondyl and a phytosaur in the Caturrita Formation reinforces the hypothesis of a change to more humid climatic conditions in the Paraná Basin during the Upper Triassic. The record of Early Triassic stereospondyls in South America suggests that they first colonized Brazil and/or Uruguay, spreading from South Africa during the Early Triassic, subsequently reaching Argentina. Up till now, there is no record of Middle Triassic stereospondyls in either Argentina and Brazil, probably due to either taphonomic bias or insufficient prospecting. Despite the lack of direct evidence, one should not dismiss an earlier stereospondyl colonization of Argentina still during the Early or Middle Triassic. © 2008 International Association for Gondwana Research. Published by Elsevier B.V. All rights reserved.
1. Introduction Stereospondyls are derived temnospondyls that invaded Gondwana during the Late Permian (Warren et al., 2000). According to these authors, they probably survived the Permo-Triassic extinctions in a refuge within the landmass that nowadays comprises Australia. The sister taxon of Stereospondyli, the archegosaurs, is present in Northern Gondwana (in Permian deposits from Brazil and India) (Price, 1948, Cox and Hutchinson, 1991 and Warren et al., 2000). Their absence from Kazakhstan and Siberia support the hypothesis of a route across northern Gondwana, still during early Late Permian, reaching a refuge in eastern Gondwana very close to the PermoTriassic boundary (Warren et al., 2000). The presence of a derived stereospondyl (Trucheosaurus major) in Upper Permian deposits from Australia supports this hypothesis (Marsicano and Warren, 1998; Warren et al., 2000). Subsequently, they radiated to other parts of Gondwana and Laurasia, reaching their highest distribution and diversification during the Early Triassic. Indeed, all representative clades of stereospondyls are widespread in deposits from Gondwana
⁎ Corresponding author. Fax: +55 5532326075. E-mail addresses: [email protected] (S. Dias-da-Silva), [email protected] (E.V. Dias), [email protected] (C.L. Schultz).
(South America, South Africa, Madagascar, Antarctica, Australia, and India, see Schoch and Milner, 2000; Yates and Warren, 2000, Warren and Marsicano, 2000, Damiani, 2001, Sidor et al., 2007). As stated by Steyer (2002, 2003), the Early Triassic radiation of stereospondyls could probably have been facilitated by their possible marine readaptation (cf. the marine stereospondyls of Madagascar). However, taking into account the high level of coalition of Pangaea during the Triassic, a migration through fresh water bodies is also probable. Temnospondyl stereospondyls are among the most frequently encountered tetrapods in Triassic continental deposits. Late Triassic stereospondyl temnospondyls were only known in South America from deposits located in central-western Argentina. There are four described Upper Triassic (Carnian to Norian) Argentinean stereospondyl taxa: the mastodonsaurid Promastodontosaurus bellmanni from the Ischigualasto Formation (Ischigualasto Basin); the chigutisaurids Pelorocephalus mendonzensis and P. cacheutensis, both from the Cacheuta Formation (Cuyana Basin) and P. tenax, from the Rio Blanco Formation (Cuyana Basin). In addition, an undetermined brachyopoid is recorded in the Cacheuta Formation (see Bonaparte, 1963; Marsicano, 1999, 2005). In contrast, the temnospondyl record in Brazil and Uruguay is a mixture of non-stereospondyl temnospondyls, basal stereospondyls and advanced stereospondyls restricted to Upper Permian–Lower Triassic levels. From the Upper Permian, there are two long snouted archegosaurids already described, Prionosuchus plummeri, from
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Northern Brazil (Pedra de Fogo Formation, Parnaíba Basin) (Price,1948; Cox and Hutchinson, 1991) and Bageherpeton longignathus, from Southern Brazil (Morro Pelado Member, Rio do Rasto Formation, Paraná Basin) (Dias and Barberena, 2001). In addition, basal representatives of stereospondyls, namely rhinesuchids, are recorded in Upper Permian deposits from Brazil: an unclassified mandible (from Morro Pelado Member) (Malabarba et al., 2003), the long snouted Australerpeton cosgriffi, and a short snouted unclassified rhinesuchid skull, both from the locality of Serra do Cadeado (Rio do Rasto Formation) (Barberena, 1998; Barberena and Dias, 1998; Dias and Schultz, 2003). One could argue that subsequent stereospondyls found in South American Triassic strata are descendants of rhinesuchids. However, phylogenetic data of stereospondyls suggest that there is no direct relationship between them and Lower Triassic taxa from South America (see Yates and Warren, 2000). In other words, rhinesuchids colonized Gondwana during the Permian and disappeared in the landmass that nowadays comprises South America prior to the PermoTriassic extinctions. This group survived as a relict occurrence in South Africa during the Lower Triassic. Hence, the subsequent stereospondyl fauna from South America represents a reinvasion of this landmass during the Early Triassic. Moreover, according to Damiani (2004), the taxonomy of rhinesuchids is problematic and a forthcoming revision of their anatomy and taxonomy is necessary in order to resolve their phylogenetic relationships.
The record of stereospondyls from the Brazilian Lower Triassic (Sanga do Cabral Formation, Paraná Basin) comprises dermal skull fragments tentatively attributed to ‘lydekkerinids’ and rhytidosteids (Lavina and Barberena, 1985; Dias-da-Silva et al., 2005) and the rhytidosteid Sangaia lavinai (Dias-da-Silva et al., 2006; Dias-daSilva and Marsicano 2006). In Uruguay, strata close to the PermoTriassic boundary have yielded a poorly preserved dvinosauroid and mastodonsauroids, and the laidlerid Uruyiella liminea, both from the Buena Vista Formation (Marsicano et al., 2000; Piñeiro et al., 2007a,b,c). The new stereospondyl described herein constitutes the first undoubted occurrence of a member of this group in Upper Triassic strata from Brazil (Caturrita Formation, Paraná Basin). Indeed, this is the only stereospondyl record for the whole Santa Maria Supersequence (sensu Zerfass et al., 2003), which includes also the Santa Maria Formation and its plentiful tetrapod record. The Caturrita Formation also bears a rich tetrapod fauna including dinosaur remains, non-mammalian therapsids, procolophonids and sphenodontids (see Langer et al., 2007). The presence of an amphibian within this fauna corroborates the sedimentological evidences towards a more humid climate at the time of deposition of these layers, represented by an increase in the rate of arenous fluvial/lacustrine deposits formed at the transition from Santa Maria to Caturrita Formation (the Santa Maria 2 third order Sequence from Zerfass et al., 2003).
Fig. 1. In A, Triassic Sequences from Southern Brazil. See the stratigraphic position of Mammaliamorpha Cenozone. Abreviations of the ages: Any, Anysian; Car, Carnian; Ind, Induan; J, Jurassic; K, Cretaceous; Lad, Ladinian; Nor, Norian; Ole, Olenekian; P, Permian; Rha, Rhaetic. In B, geographic location of the Botucaraí Oucrop in South America. The simbol (⁎) indicates the location of the outcrop. Modified from Zerfass et al. (2003), and Vega-Dias and Schultz (2004).
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Fig. 2. Composite photograph of the southern margin of the “Botucaraí Outcrop” (above) and its schematic section (below). D = Disconformity; SD= Subaqüous Dunes; SL= Sigmoidal Lobes; TB= Lacustrine Turbidites. The arrows indicate the level from where the fossil was recovered. UFRGS PV 1059 T was found in a disconformity between the SD facies and the SL facies.
Institutional abbreviations. UFRGS, Universidade Federal do Rio Grande do Sul; PV, Paleovertebrate collection; T, Triassic. 2. Geological Setting The Triassic infilling of the Paraná Basin in southern Brazil (Rosário do Sul Group) is entirely non-marine (Pierini et al., 2002; Zerfass et al., 2003). In terms of sequence stratigraphy, according to Zerfass et al. (2003) the Middle–Upper Triassic of the Rio Grande do Sul State corresponds to a second order sequence (Fig. 1), denominated Santa Maria Supersequence. It is divided into three third-order sequences: the Santa Maria 1 (Ladinian age), Santa Maria 2 (Carnian age) and Santa Maria 3 (Rhaetian–Early Jurassic age) sequences. Each of these
third-order sequences begins with fluvial deposits of low sinuosity rivers covered by transgressive shallow lacustrine rocks. The stereospondyl material here discussed was collected at the northern margin of the so-called “Botucaraí Outcrop”, a road cut sited at the margins of BR-287 road, near the Botucaraí Hillock, 6 km west of the entrance to Candelária City, Rio Grande do Sul State (coordinates 29° 40′ 48″ S ; 52° 50′ 24″ W). The siltstones and fine-grained sandstones beds that crop out in this area are lithostratigraphycally included in the Upper Triassic Caturrita Formation (Andreis et al., 1980) and are interpreted as deposited in a fluvial-deltaic environment (Fig. 2). This unit is part of the Santa Maria 2 third order Sequence of Zerfass et al. (2003). Recently, the same author (Zerfass, 2007) after a detailed mapping of an area located about 100 km W
Fig. 3. Stereospondyl interclavicle UFRGS PV 1059 T from the Upper Triassic of Southern Brazil in ventral view. In A photograph; in B, interpretative drawing; in C, estimated outline. Scale bar equals 10 mm (C not to scale).
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from the Botucarai Outcrop, encountered a disconformity between the Santa Maria and Caturrita formations and interpreted the last one as an individual third-order sequence, called Caturrita Sequence. If such disconformity could be extended to the area of the Botucaraí Outcrop, it would be placed below the level where the stereospondyl was found (so this level clearly belongs to the Caturrita Formation, based on its facies and paleofauna). The nearest fossil bearing outcrop from the Santa Maria Formation (which includes Hyperodapedon, Barberenachampsa and Exaeretodon) is located 7 km W (and at least 30 m below) from the Botucaraí Outcrop.
vicle the distance between ridges is even more obvious. The dorsal surface of UFRGS PV 1059 T is flat, with no signal of processes or depressions. Therefore is uninformative for taxonomic purposes.
2.1. The age and faunal content of the Caturrita Formation Rubert and Schultz (2004) proposed the “Ictidosaur Association Zone” for the fossiliferous beds of the Caturrita Formation based on the presence of a distinct tetrapod association characterized by little nonmammalian “ictidosaurian” cynodonts, including Riograndia guaibensis, Irajatherium hernandezi, Brasilodon quadrangularis and Brasilitherium riograndensis. In addition to the non-mammalian cynodonts, the procolophonid Soturnia caliodon, the dinosaurs Guaibasaurus candelariensis and Unaysaurus tolentinoi, the dicynodont Jachaleria candelariensis, the sphenodontid Clevosaurus brasiliensis, an indeterminate phytosaur and footprints attributed to prosauropod dinosaurs also characterized the Caturrita tetrapod fauna. For the complete set of taxonomic references, see da Silva et al. (2007) and Langer et al. (2007). The putative “ictidosaurs” mentioned above were recently moved (Soares, 2004) to Tritheledontidae (Riograndia and Irajatherium) and Brasilodontidae (Brasilodon and Brasilitherium) which are considered stem-groups of Mammalia, and thus included in the clade Mammaliamorpha (Soares and Schultz, 2006). Therefore, Schultz and Soares (2006) proposed to change the name “Ictidosaur Association Zone” for the fossiliferous levels of the Caturrita Formation to the “Mammaliamorpha Cenozone”. This cenozone is correlated with the “early Coloradian stage” from Argentina, which is considered early Norian in age (Rubert and Schultz 2004). 3. Systematic Paleontology Temnospondyli von Zittel 1888 Stereospondylomorpha Yates and Warren 2000 Stereospondyli von Zittel 1888 Mastodonsauroidea? (sensu Damiani, 2001) indet. 3.1. Material UFRGS PV 1059 T, an incomplete interclavicle (Fig. 3A, B). 3.2. Locality and Horizon Botucaraí Hillock, 6 km west of the entrance to Candelária City, Rio Grande do Sul State, Brazil. Upper Carnian to Lower Norian of Paraná Basin (Rubert and Schultz, 2004; Bonaparte and Sues, 2006; Langer et al., 2007). 3.3. Description The material consists of an incomplete interclavicle of flattened rhomboidal shape (11 mm tick, 112 mm wide, and 161 mm long). The ventral surface of the interclavicles is covered by a coarse spider web reticulate pattern, characterized by straight ridges that radiate from the ossification centre. The ridges are shallow (deepness of about 1.5 mm) and are interconnected by relatively wide crests; nodes or pustules are absent. This type of ornamentation is similar to that present in Almasaurus (Warren and Snell, 1991), Siderops (Warren and Marsicano, 2000) and indeterminate brachyopoid material from Argentina (Marsicano, 1993). Nevertheless, in the Brazilian intercla-
Fig. 4. Interclavicular pattern amongst different groups of stereospondyls. In A, Metoposauridae (modified from Chowdhury, 1965); in B, mastodonsauroid Mastodonsaurus giganteous (modified from Schoch and Milner, 2000); in C indeterminate brachyopoid from Argentina (modified from Marsicano,1993); in D, mastodonsauroid Promastodonsaurus bellmanni with attached clavicles (modified from Bonaparte, 1963). Since these elements are for comparison to UFRGS PV 1059 T (being of different sizes), none of them is to scale.
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According to the strong ossification degree of this dermal bone and its heavy ornamentation, the specimen probably belonged to an adult individual (see Steyer 2000, and Steyer et al., 2004 for the somatic age criteria of the temnospondyls). In spite of the poor preservation of the external borders of the material it presents the flattened rhomboidal shape, little longer than wide, typical of stereospondylomorphs. A strip of ornamentation, which presumably extended to the anterior tip of the interclavicle thus, separates the clavicular articular facets; the clavicles when articulated did not completely overlap the interclavicular blade. According to Warren and Snell (1991), this is the condition present in Mastodonsauridae and Almasauridae, and some Permian taxa as Eryops. Conversely, in the Triassic Metoposauridae, Trematosauridae, Capitosauridae, Benthosuchidae, Plagiosauridae, and Siderops the clavicular facets meet anteriorly so the interclavicular stem lacks any ornamentation (Warren and Snell, 1991). The centre of ossification of the interclavicle is apparently located posterior to the level of the maximum width of the interclavicular blade. In metoposaurids (Fig. 4A), the centre of ossification is situated markedly posterior to this point, while in mastodonsaurids (including Promastodontosaurus) and the rhinesuchid Australerpeton just posteriorly located (Warren and Snell, 1991; Dias and Schultz, 2003). This condition presumably occurs in the Brazilian specimen. 4. Discussion Non-stereospondyl temnospondyls are quite rare in Mesozoic deposits. In fact, by the beginning of the Triassic all major stereospondyl clades were already established in Pangaea (e.g. Schoch and Milner, 2000; Warren and Marsicano, 2000; Yates and Warren, 2000; Damiani, 2001). Although the interclavicle here described is not associated with cranial material that would assure a more accurate taxonomic assignation, it is more likely to represent a stereospondyl temnospondyl taxon. Within Stereospondyli, the general rhomboidal shape, the pattern of sculpture and the thickness of the Brazilian interclavicle relate it with those described for mastodonsauroids (Schoch and Milner, 2000, and Damiani, 2001) (Fig. 4B) and almasaurids (Warren and Snell, 1991). Upper Triassic South American stereospondyls with interclavicular elements preserved are restricted to the mastodonsauroid Promastodontosaurus bellmanni and indeterminate brachyopoid material both from the Upper Triassic of central-western Argentina (Fig. 4C) (Bonaparte, 1963; Marsicano, 1993). In UFRGS PV 1059 T, the centre of ossification is presumably located behind the level of the maximum width of the interclavicular blade. A condition quite similar to that found to the neighbor Argentinean mastodonsauroid Promastodontosaurus (Bonaparte, 1963) (Fig. 4D). In fact, UFRGS PV 1059 T is remarkably similar to the interclavicle of Mastodonsaurus giganteous (Fig. 4B), especially regarding the pattern of ornamentation. Therefore, it is reasonable to assume that this group might have been present in Upper Triassic environments from Southern Brazil. Further corroboration provided by more complete material is necessary to reinforce this hypothesis. The tetrapod content of the Upper Triassic Caturrita Formation is rich and diversified; however, stereospondyls were unknown from this unit until now. In spite of the difficulty to assign this new specimen to a less inclusive group, its presence in the Upper Triassic of Brazil corroborate the hypothesis of Marsicano (2005), who suggested that temnospondyls were probably more diversified in this part of Gondwana during the Late Triassic than it is evidenced by the fossil record. So far, the discovery of this stereospondyl constitutes a single record for the Middle–Upper Triassic package of southern Brazil. This package includes the Santa Maria and Caturrita formations, both characterized by the presence of abundant fossil terrestrial tetrapod faunas. Nevertheless, the presence of aquatic or even semi-aquatic
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forms within these faunas, in the whole Santa Maria 1 Sequence and in the lower part of Santa Maria 2 Sequence is rare (restricted only to a few proterochampsid archosaurs (Chañaresuchus, Cerritosaurus and Barberenachampsa). Besides, no fossil fishes or aquatic invertebrates were encountered associated to the tetrapods. In spite of the preservation of these fossils in floodplain deposits, the availability of permanent water bodies would be insufficient to maintain aquatic forms of life. Towards the top of the Santa Maria 2 Sequence, the transition from Santa Maria to Caturrita Formation is characterized by an increase of sandy facies represented by fluvial\deltaic deposits. This indicates a change to more humid climatic conditions at that time, and the presence of a phytosaur and an amphibian in the faunal assemblage of the Caturrita Formation reinforces such hypothesis. Regarding the paleobiogeography of advanced stereospondyls in South America, the presence of rhytidosteids in Lower Triassic deposits from Brazil, as well as mastodonsaurids and the enigmatic Uruyiella liminea in Permo-Triassic deposits from Uruguay (Dias-daSilva et al., 2005, 2006; Piñeiro et al., 2007a,b,c) suggests that they first colonized Brazil and Uruguay, probably spreading from South Africa. Later, they reached Argentina during late Early, Middle or Late Triassic. It is important to point out that Lower Triassic deposits are quite rare in Argentina. Therefore, an alternative scenario cannot be dismissed, with stereospondyls colonizing the Argentinean Gondwana still during Early or Middle Triassic. Unfortunately, the small amount of information regarding the Lower Triassic in Argentina is an obstacle to clarify the sequence of events related to the diversification of stereospondyls in this part of Gondwana. Besides, to the present, there is no record of stereospondyls in Middle Triassic deposits from both Argentina and Brazil. Alternative explanations for their absence in the Middle Triassic of South America are either taphonomic bias or insufficient prospecting in deposits of this age. Stereospondyls (and other aquatic animals), tend to be less represented than other vertebrate groups, due to taphonomic bias, because the fluvial style causes a direct impact on the taphonomic mode of preservation. According to Fonseca and Scherer (1998) and Pires et al. (2005) the Triassic was marked by a large degree of seasonality, with large dry periods replaced by shorter periods of humidity. The increasing of humidity towards the top of the Triassic succession modified the fluvial environments from anastomosed to braided systems (Fonseca and Scherer, 1998). In braided systems, intense reworking tends to destroy delicate bones. Therefore, animals with slender skeletons (e. g. stereospondyls and phytosaurs) are likely to be less represented in this kind of depositional environment. In conclusion, further prospecting efforts are necessary in order to clarify the likely sequence of events related with the diversification of stereospondyls in South American Gondwana which would further contribute to our understanding of the evolution of West Gondwana (Vaughan and Pankhurst, 2008), as well as the paleobiogeography of crustal fragments in the erstwhile Gondwana assembly (cf. Meert and Lieberman, 2008). Acknowledgements SDS would like to thank the Universidade Federal do Pampa/UFSM, for the facilities provided during the present study, Claudia Marsicano for a critical review of an earlier version of this manuscript, Cristina Machado-Bertoni for her useful taphonomic insights, Juan Carlos Cisneros for the interpretative drawing of the Brazilian interclavicle (Fig. 3B), and Lúcia Helena do Canto Vinadé for English revision. In addition, we thank Jean Sébastien Steyer and an anonymous referee for their suggestions that greatly improved the manuscript. References Andreis, R., Bossi, G.E., Montardo, D.K., 1980. O Grupo Rosário do Sul (Triássico) no Rio Grande do Sul. 659–673. In: Monaco, O.A. (Ed.), Anais do XXXI Congresso Brasileiro de Geologia, Camboriú, Santa Catarina. Sociedade Brasileira de Geologia, São Paulo, Brazil, p. 1309.
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Piñeiro, G., Marsicano, C., Goso, C., Morosi, E., 2007c. Temnospondyl diversity of the Permian-Triassic Colônia Orozco Local Fauna (Buena Vista Formation) of Uruguay. Revista Brasileira de Paleontologia 10, 169–180. Pires, E.F., Sommer, M.G., Scherer, C.M.S., 2005. Late Triassic climate in southernmost Parana Basin (Brazil): evidence from dendrochronological data. Journal of South American Earth Sciences 18, 213–221. Pierini, C., Mizusaki, A.M., Scherer, C.M.S., Alves, D.B., 2002. Integrated stratigraphic and geochemical study of the Santa Maria and Caturrita formations (Triassic of the Paraná Basin), southern Brazil. Journal of South American Earth Sciences 15, 669–681. Price, L.I., 1948. Um anfíbio labirintodonte da Formação Pedra do Fogo, Estado do Maranhão. Boletim do Ministério da Agricultura - Departamento Nacional de Produção Mineral, divisão de Geologia e Mineralogia, vol. 124, pp. 7–32. Rubert, R.R., Schultz, C.L., 2004. Um novo horizonte de correlação para o Triássico Superior do Rio Grande do Sul. Pesquisas 31, 71–88. Schoch, R.R., Milner, A.R., 2000. In: Wellnhofer, P., München (Eds.), Handbuch der Paläoherpetologie, Encyclopedia of Paleoherpetology – Stereospondyli, Part 3B. Verlag Dr. Friedrich Pfeil, München, Germany. Schultz, C.L., Soares, M.B., 2006. Proposta de nova denominação para a Cenozona de Ictidosauria do Triássico Superior (Formação Caturrita do Rio Grande do Sul). Ciência and Natura, Edição Especial-Agosto/2006 (V Simpósio Brasileiro de Paleontologia de Vertebrados), p. 41. Sidor, C.A., Steyer, J.S., Damiani, R., 2007. Parotosuchus (Temnospondyli: Mastodonsauridae) from the Triassic of Antarctica. Journal of Vertebrate Paleontology 27, 232–235. Soares, M.B., 2004, Novos materiais de Riograndia guaibensis (Cynodontia, Tritheledontidae) do Triássico Superior do Rio Grande do Sul, Brasil:análise osteológica e implicações filogenéticas. Ph.D. thesis, Universidade Federal do Rio Grande do Sul. Soares, M.B., Schultz, C.L., 2006. A hipótese filogenética Brasilodontidae-Mammalia e sua implicação na redefinição do Clado Mammaliamorpha. Ciência and Natura, Edição Especial-Agosto/2006 (V Simpósio Brasileiro de Paleontologia de Vertebrados), p. 40. Steyer, J.S., 2000. Ontogeny and phylogeny in temnospondyls: a new method of analysis. Zoological Journal of the Linnean Society 130, 449–467. Steyer, J.S., 2002. The first articulated trematosaur ‘amphibian’ from the Lower Triassic of Madagascar: implications for the phylogeny of the group. Palaeontology 45, 771–793. Steyer, J.S., 2003. A revision of the Early Triassic ‘‘Capitosaurs’’ (Stegocephali, Stereospondyli) from Madagascar, with remarks on their comparative ontogeny. Journal of Vertebrate Paleontology 23, 544–555. Steyer, J.S., Laurin, M., Castanet, J., de Ricqle`s, A., 2004. First histological and skeletochronological data on temnospondyl growth: palaeoecological and palaeoclimatological implications. Palaeogeography, Palaeoclimatology, Palaeoecology 206, 193–201. Vaughan, A.M., Pankhurst, R.J., 2008. Tectonic overview of the West Gondwana margin. Gondwana Research 13, 150–162. Vega-Dias, C., Schultz, C.L., 2004. Postcranial material of Jachaleria candelariensis Araújo and Gonzaga 1980 (Therapsida, Dicynodontia), Upper Triassic of Rio Grande do Sul, Brazil. Paleobios, PaleoBios 24, 7–31. von Zittel, K., 1888. Ueber “Labyrinthodon rütimeyeri Wiedersheim”. N. Jb. Min. Geol. Paläont. 1888, 257–258. Warren, A.A., Marsicano, C.A., 2000. A Phylogeny of the Brachyopoidea (Temnospondyli, Stereospondyli). Journal of Vertebrate Paleontology 20, 462–483. Warren, A.A., Snell, N., 1991. The postcranial skeleton of Mesozoic temnospondyl amphibians: a review. Alcheringa 15, 43–64. Warren, A.A., Damiani, R., Yates, A.M., 2000. Paleobiogeography of Australian Fossil Amphibians. Historical Biology 15, 171–179. Yates, A.M., Warren, A.A., 2000. The phylogeny of the ‘higher’ temnospondyls (Vertebrata: Choanata) and its implications for the monophyly and origins of the Stereospondyls. Zoological Journal of the Linnean Society 128, 77–121. Zerfass, H. 2007. Geologia da Folha Agudo, SH.22-V-C-V, escala 1:100.000. Serviço Geológico do Brasil - CPRM, CD-ROM. Zerfass, H., Lavina, E.L., Schultz, C.L., Garcia, A.J.V., Faccini, U.F., Chemale Jr., F., 2003. Sequence stratigraphy of continental Triassic strata of southernmost Brazil: a contribution to southwestern Gondwana palaeogeography and palaeoclimate. Sedimentary Geology 161, 85–105.
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Gondwana Research j o u r n a l h o m e p a g e : w w w. e l s e v i e r. c o m / l o c a t e / g r
GR Letter
First record of stereospondyls (Tetrapoda, Temnospondyli) in the Upper Triassic of Southern Brazil Sérgio Dias-da-Silva a,⁎, Eliseu Vieira Dias b, Cesar Leandro Schultz c a
Centro de Ciências Rurais, Universidade Federal do Pampa, Campus de São Gabriel, Avenida Antônio Trilha, 1847, Bairro Centro, CEP 97.300-000, São Gabriel, Rio Grande do Sul, Brasil Centro Universitário Positivo, Núcleo de Ciências Biológicas e da Saúde, Rua Prof. Pedro Viriato Parigot de Souza, 5.300, CEP 81.280-330, Curitiba, Paraná, Brasil Laboratório de Paleovertebrados, Departamento de Paleontologia e Estratigrafia, Instituto de Geociências, Universidade Federal do Rio Grande do Sul, Avenida Bento Gonçalves, 9.500 prédio 43.127/110 B, CEP: 91.540-000, Porto Alegre, Rio Grande do Sul, Brazil
b c
a r t i c l e
i n f o
Article history: Received 21 October 2007 Received in revised form 16 July 2008 Accepted 16 July 2008 Available online 24 July 2008 Keywords: Temnospondyli Western Gondwana Paleobiogeography Rosário do Sul Group Santa Maria Supersequence
a b s t r a c t Stereospondyls survived the Permo-Triassic extinctions in a refuge probably located in the landmass that nowadays comprises Australia. Subsequently, they radiated to other parts of Pangaea, reaching their highest distribution and diversification during the Early Triassic. An incomplete interclavicle from the Caturrita Formation represents their first record in the Upper Triassic of Brazil. Previously, Upper Triassic South American stereospondyls were restricted to Argentina. This new record reinforces a former hypothesis that suggests the presence of a more diverse stereospondyl fauna in South America during the Late Triassic than previously assumed. Additionally, the presence of a stereospondyl and a phytosaur in the Caturrita Formation reinforces the hypothesis of a change to more humid climatic conditions in the Paraná Basin during the Upper Triassic. The record of Early Triassic stereospondyls in South America suggests that they first colonized Brazil and/or Uruguay, spreading from South Africa during the Early Triassic, subsequently reaching Argentina. Up till now, there is no record of Middle Triassic stereospondyls in either Argentina and Brazil, probably due to either taphonomic bias or insufficient prospecting. Despite the lack of direct evidence, one should not dismiss an earlier stereospondyl colonization of Argentina still during the Early or Middle Triassic. © 2008 International Association for Gondwana Research. Published by Elsevier B.V. All rights reserved.
1. Introduction Stereospondyls are derived temnospondyls that invaded Gondwana during the Late Permian (Warren et al., 2000). According to these authors, they probably survived the Permo-Triassic extinctions in a refuge within the landmass that nowadays comprises Australia. The sister taxon of Stereospondyli, the archegosaurs, is present in Northern Gondwana (in Permian deposits from Brazil and India) (Price, 1948, Cox and Hutchinson, 1991 and Warren et al., 2000). Their absence from Kazakhstan and Siberia support the hypothesis of a route across northern Gondwana, still during early Late Permian, reaching a refuge in eastern Gondwana very close to the PermoTriassic boundary (Warren et al., 2000). The presence of a derived stereospondyl (Trucheosaurus major) in Upper Permian deposits from Australia supports this hypothesis (Marsicano and Warren, 1998; Warren et al., 2000). Subsequently, they radiated to other parts of Gondwana and Laurasia, reaching their highest distribution and diversification during the Early Triassic. Indeed, all representative clades of stereospondyls are widespread in deposits from Gondwana
⁎ Corresponding author. Fax: +55 5532326075. E-mail addresses: [email protected] (S. Dias-da-Silva), [email protected] (E.V. Dias), [email protected] (C.L. Schultz).
(South America, South Africa, Madagascar, Antarctica, Australia, and India, see Schoch and Milner, 2000; Yates and Warren, 2000, Warren and Marsicano, 2000, Damiani, 2001, Sidor et al., 2007). As stated by Steyer (2002, 2003), the Early Triassic radiation of stereospondyls could probably have been facilitated by their possible marine readaptation (cf. the marine stereospondyls of Madagascar). However, taking into account the high level of coalition of Pangaea during the Triassic, a migration through fresh water bodies is also probable. Temnospondyl stereospondyls are among the most frequently encountered tetrapods in Triassic continental deposits. Late Triassic stereospondyl temnospondyls were only known in South America from deposits located in central-western Argentina. There are four described Upper Triassic (Carnian to Norian) Argentinean stereospondyl taxa: the mastodonsaurid Promastodontosaurus bellmanni from the Ischigualasto Formation (Ischigualasto Basin); the chigutisaurids Pelorocephalus mendonzensis and P. cacheutensis, both from the Cacheuta Formation (Cuyana Basin) and P. tenax, from the Rio Blanco Formation (Cuyana Basin). In addition, an undetermined brachyopoid is recorded in the Cacheuta Formation (see Bonaparte, 1963; Marsicano, 1999, 2005). In contrast, the temnospondyl record in Brazil and Uruguay is a mixture of non-stereospondyl temnospondyls, basal stereospondyls and advanced stereospondyls restricted to Upper Permian–Lower Triassic levels. From the Upper Permian, there are two long snouted archegosaurids already described, Prionosuchus plummeri, from
1342-937X/$ – see front matter © 2008 International Association for Gondwana Research. Published by Elsevier B.V. All rights reserved. doi:10.1016/j.gr.2008.07.002
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Northern Brazil (Pedra de Fogo Formation, Parnaíba Basin) (Price,1948; Cox and Hutchinson, 1991) and Bageherpeton longignathus, from Southern Brazil (Morro Pelado Member, Rio do Rasto Formation, Paraná Basin) (Dias and Barberena, 2001). In addition, basal representatives of stereospondyls, namely rhinesuchids, are recorded in Upper Permian deposits from Brazil: an unclassified mandible (from Morro Pelado Member) (Malabarba et al., 2003), the long snouted Australerpeton cosgriffi, and a short snouted unclassified rhinesuchid skull, both from the locality of Serra do Cadeado (Rio do Rasto Formation) (Barberena, 1998; Barberena and Dias, 1998; Dias and Schultz, 2003). One could argue that subsequent stereospondyls found in South American Triassic strata are descendants of rhinesuchids. However, phylogenetic data of stereospondyls suggest that there is no direct relationship between them and Lower Triassic taxa from South America (see Yates and Warren, 2000). In other words, rhinesuchids colonized Gondwana during the Permian and disappeared in the landmass that nowadays comprises South America prior to the PermoTriassic extinctions. This group survived as a relict occurrence in South Africa during the Lower Triassic. Hence, the subsequent stereospondyl fauna from South America represents a reinvasion of this landmass during the Early Triassic. Moreover, according to Damiani (2004), the taxonomy of rhinesuchids is problematic and a forthcoming revision of their anatomy and taxonomy is necessary in order to resolve their phylogenetic relationships.
The record of stereospondyls from the Brazilian Lower Triassic (Sanga do Cabral Formation, Paraná Basin) comprises dermal skull fragments tentatively attributed to ‘lydekkerinids’ and rhytidosteids (Lavina and Barberena, 1985; Dias-da-Silva et al., 2005) and the rhytidosteid Sangaia lavinai (Dias-da-Silva et al., 2006; Dias-daSilva and Marsicano 2006). In Uruguay, strata close to the PermoTriassic boundary have yielded a poorly preserved dvinosauroid and mastodonsauroids, and the laidlerid Uruyiella liminea, both from the Buena Vista Formation (Marsicano et al., 2000; Piñeiro et al., 2007a,b,c). The new stereospondyl described herein constitutes the first undoubted occurrence of a member of this group in Upper Triassic strata from Brazil (Caturrita Formation, Paraná Basin). Indeed, this is the only stereospondyl record for the whole Santa Maria Supersequence (sensu Zerfass et al., 2003), which includes also the Santa Maria Formation and its plentiful tetrapod record. The Caturrita Formation also bears a rich tetrapod fauna including dinosaur remains, non-mammalian therapsids, procolophonids and sphenodontids (see Langer et al., 2007). The presence of an amphibian within this fauna corroborates the sedimentological evidences towards a more humid climate at the time of deposition of these layers, represented by an increase in the rate of arenous fluvial/lacustrine deposits formed at the transition from Santa Maria to Caturrita Formation (the Santa Maria 2 third order Sequence from Zerfass et al., 2003).
Fig. 1. In A, Triassic Sequences from Southern Brazil. See the stratigraphic position of Mammaliamorpha Cenozone. Abreviations of the ages: Any, Anysian; Car, Carnian; Ind, Induan; J, Jurassic; K, Cretaceous; Lad, Ladinian; Nor, Norian; Ole, Olenekian; P, Permian; Rha, Rhaetic. In B, geographic location of the Botucaraí Oucrop in South America. The simbol (⁎) indicates the location of the outcrop. Modified from Zerfass et al. (2003), and Vega-Dias and Schultz (2004).
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Fig. 2. Composite photograph of the southern margin of the “Botucaraí Outcrop” (above) and its schematic section (below). D = Disconformity; SD= Subaqüous Dunes; SL= Sigmoidal Lobes; TB= Lacustrine Turbidites. The arrows indicate the level from where the fossil was recovered. UFRGS PV 1059 T was found in a disconformity between the SD facies and the SL facies.
Institutional abbreviations. UFRGS, Universidade Federal do Rio Grande do Sul; PV, Paleovertebrate collection; T, Triassic. 2. Geological Setting The Triassic infilling of the Paraná Basin in southern Brazil (Rosário do Sul Group) is entirely non-marine (Pierini et al., 2002; Zerfass et al., 2003). In terms of sequence stratigraphy, according to Zerfass et al. (2003) the Middle–Upper Triassic of the Rio Grande do Sul State corresponds to a second order sequence (Fig. 1), denominated Santa Maria Supersequence. It is divided into three third-order sequences: the Santa Maria 1 (Ladinian age), Santa Maria 2 (Carnian age) and Santa Maria 3 (Rhaetian–Early Jurassic age) sequences. Each of these
third-order sequences begins with fluvial deposits of low sinuosity rivers covered by transgressive shallow lacustrine rocks. The stereospondyl material here discussed was collected at the northern margin of the so-called “Botucaraí Outcrop”, a road cut sited at the margins of BR-287 road, near the Botucaraí Hillock, 6 km west of the entrance to Candelária City, Rio Grande do Sul State (coordinates 29° 40′ 48″ S ; 52° 50′ 24″ W). The siltstones and fine-grained sandstones beds that crop out in this area are lithostratigraphycally included in the Upper Triassic Caturrita Formation (Andreis et al., 1980) and are interpreted as deposited in a fluvial-deltaic environment (Fig. 2). This unit is part of the Santa Maria 2 third order Sequence of Zerfass et al. (2003). Recently, the same author (Zerfass, 2007) after a detailed mapping of an area located about 100 km W
Fig. 3. Stereospondyl interclavicle UFRGS PV 1059 T from the Upper Triassic of Southern Brazil in ventral view. In A photograph; in B, interpretative drawing; in C, estimated outline. Scale bar equals 10 mm (C not to scale).
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from the Botucarai Outcrop, encountered a disconformity between the Santa Maria and Caturrita formations and interpreted the last one as an individual third-order sequence, called Caturrita Sequence. If such disconformity could be extended to the area of the Botucaraí Outcrop, it would be placed below the level where the stereospondyl was found (so this level clearly belongs to the Caturrita Formation, based on its facies and paleofauna). The nearest fossil bearing outcrop from the Santa Maria Formation (which includes Hyperodapedon, Barberenachampsa and Exaeretodon) is located 7 km W (and at least 30 m below) from the Botucaraí Outcrop.
vicle the distance between ridges is even more obvious. The dorsal surface of UFRGS PV 1059 T is flat, with no signal of processes or depressions. Therefore is uninformative for taxonomic purposes.
2.1. The age and faunal content of the Caturrita Formation Rubert and Schultz (2004) proposed the “Ictidosaur Association Zone” for the fossiliferous beds of the Caturrita Formation based on the presence of a distinct tetrapod association characterized by little nonmammalian “ictidosaurian” cynodonts, including Riograndia guaibensis, Irajatherium hernandezi, Brasilodon quadrangularis and Brasilitherium riograndensis. In addition to the non-mammalian cynodonts, the procolophonid Soturnia caliodon, the dinosaurs Guaibasaurus candelariensis and Unaysaurus tolentinoi, the dicynodont Jachaleria candelariensis, the sphenodontid Clevosaurus brasiliensis, an indeterminate phytosaur and footprints attributed to prosauropod dinosaurs also characterized the Caturrita tetrapod fauna. For the complete set of taxonomic references, see da Silva et al. (2007) and Langer et al. (2007). The putative “ictidosaurs” mentioned above were recently moved (Soares, 2004) to Tritheledontidae (Riograndia and Irajatherium) and Brasilodontidae (Brasilodon and Brasilitherium) which are considered stem-groups of Mammalia, and thus included in the clade Mammaliamorpha (Soares and Schultz, 2006). Therefore, Schultz and Soares (2006) proposed to change the name “Ictidosaur Association Zone” for the fossiliferous levels of the Caturrita Formation to the “Mammaliamorpha Cenozone”. This cenozone is correlated with the “early Coloradian stage” from Argentina, which is considered early Norian in age (Rubert and Schultz 2004). 3. Systematic Paleontology Temnospondyli von Zittel 1888 Stereospondylomorpha Yates and Warren 2000 Stereospondyli von Zittel 1888 Mastodonsauroidea? (sensu Damiani, 2001) indet. 3.1. Material UFRGS PV 1059 T, an incomplete interclavicle (Fig. 3A, B). 3.2. Locality and Horizon Botucaraí Hillock, 6 km west of the entrance to Candelária City, Rio Grande do Sul State, Brazil. Upper Carnian to Lower Norian of Paraná Basin (Rubert and Schultz, 2004; Bonaparte and Sues, 2006; Langer et al., 2007). 3.3. Description The material consists of an incomplete interclavicle of flattened rhomboidal shape (11 mm tick, 112 mm wide, and 161 mm long). The ventral surface of the interclavicles is covered by a coarse spider web reticulate pattern, characterized by straight ridges that radiate from the ossification centre. The ridges are shallow (deepness of about 1.5 mm) and are interconnected by relatively wide crests; nodes or pustules are absent. This type of ornamentation is similar to that present in Almasaurus (Warren and Snell, 1991), Siderops (Warren and Marsicano, 2000) and indeterminate brachyopoid material from Argentina (Marsicano, 1993). Nevertheless, in the Brazilian intercla-
Fig. 4. Interclavicular pattern amongst different groups of stereospondyls. In A, Metoposauridae (modified from Chowdhury, 1965); in B, mastodonsauroid Mastodonsaurus giganteous (modified from Schoch and Milner, 2000); in C indeterminate brachyopoid from Argentina (modified from Marsicano,1993); in D, mastodonsauroid Promastodonsaurus bellmanni with attached clavicles (modified from Bonaparte, 1963). Since these elements are for comparison to UFRGS PV 1059 T (being of different sizes), none of them is to scale.
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According to the strong ossification degree of this dermal bone and its heavy ornamentation, the specimen probably belonged to an adult individual (see Steyer 2000, and Steyer et al., 2004 for the somatic age criteria of the temnospondyls). In spite of the poor preservation of the external borders of the material it presents the flattened rhomboidal shape, little longer than wide, typical of stereospondylomorphs. A strip of ornamentation, which presumably extended to the anterior tip of the interclavicle thus, separates the clavicular articular facets; the clavicles when articulated did not completely overlap the interclavicular blade. According to Warren and Snell (1991), this is the condition present in Mastodonsauridae and Almasauridae, and some Permian taxa as Eryops. Conversely, in the Triassic Metoposauridae, Trematosauridae, Capitosauridae, Benthosuchidae, Plagiosauridae, and Siderops the clavicular facets meet anteriorly so the interclavicular stem lacks any ornamentation (Warren and Snell, 1991). The centre of ossification of the interclavicle is apparently located posterior to the level of the maximum width of the interclavicular blade. In metoposaurids (Fig. 4A), the centre of ossification is situated markedly posterior to this point, while in mastodonsaurids (including Promastodontosaurus) and the rhinesuchid Australerpeton just posteriorly located (Warren and Snell, 1991; Dias and Schultz, 2003). This condition presumably occurs in the Brazilian specimen. 4. Discussion Non-stereospondyl temnospondyls are quite rare in Mesozoic deposits. In fact, by the beginning of the Triassic all major stereospondyl clades were already established in Pangaea (e.g. Schoch and Milner, 2000; Warren and Marsicano, 2000; Yates and Warren, 2000; Damiani, 2001). Although the interclavicle here described is not associated with cranial material that would assure a more accurate taxonomic assignation, it is more likely to represent a stereospondyl temnospondyl taxon. Within Stereospondyli, the general rhomboidal shape, the pattern of sculpture and the thickness of the Brazilian interclavicle relate it with those described for mastodonsauroids (Schoch and Milner, 2000, and Damiani, 2001) (Fig. 4B) and almasaurids (Warren and Snell, 1991). Upper Triassic South American stereospondyls with interclavicular elements preserved are restricted to the mastodonsauroid Promastodontosaurus bellmanni and indeterminate brachyopoid material both from the Upper Triassic of central-western Argentina (Fig. 4C) (Bonaparte, 1963; Marsicano, 1993). In UFRGS PV 1059 T, the centre of ossification is presumably located behind the level of the maximum width of the interclavicular blade. A condition quite similar to that found to the neighbor Argentinean mastodonsauroid Promastodontosaurus (Bonaparte, 1963) (Fig. 4D). In fact, UFRGS PV 1059 T is remarkably similar to the interclavicle of Mastodonsaurus giganteous (Fig. 4B), especially regarding the pattern of ornamentation. Therefore, it is reasonable to assume that this group might have been present in Upper Triassic environments from Southern Brazil. Further corroboration provided by more complete material is necessary to reinforce this hypothesis. The tetrapod content of the Upper Triassic Caturrita Formation is rich and diversified; however, stereospondyls were unknown from this unit until now. In spite of the difficulty to assign this new specimen to a less inclusive group, its presence in the Upper Triassic of Brazil corroborate the hypothesis of Marsicano (2005), who suggested that temnospondyls were probably more diversified in this part of Gondwana during the Late Triassic than it is evidenced by the fossil record. So far, the discovery of this stereospondyl constitutes a single record for the Middle–Upper Triassic package of southern Brazil. This package includes the Santa Maria and Caturrita formations, both characterized by the presence of abundant fossil terrestrial tetrapod faunas. Nevertheless, the presence of aquatic or even semi-aquatic
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forms within these faunas, in the whole Santa Maria 1 Sequence and in the lower part of Santa Maria 2 Sequence is rare (restricted only to a few proterochampsid archosaurs (Chañaresuchus, Cerritosaurus and Barberenachampsa). Besides, no fossil fishes or aquatic invertebrates were encountered associated to the tetrapods. In spite of the preservation of these fossils in floodplain deposits, the availability of permanent water bodies would be insufficient to maintain aquatic forms of life. Towards the top of the Santa Maria 2 Sequence, the transition from Santa Maria to Caturrita Formation is characterized by an increase of sandy facies represented by fluvial\deltaic deposits. This indicates a change to more humid climatic conditions at that time, and the presence of a phytosaur and an amphibian in the faunal assemblage of the Caturrita Formation reinforces such hypothesis. Regarding the paleobiogeography of advanced stereospondyls in South America, the presence of rhytidosteids in Lower Triassic deposits from Brazil, as well as mastodonsaurids and the enigmatic Uruyiella liminea in Permo-Triassic deposits from Uruguay (Dias-daSilva et al., 2005, 2006; Piñeiro et al., 2007a,b,c) suggests that they first colonized Brazil and Uruguay, probably spreading from South Africa. Later, they reached Argentina during late Early, Middle or Late Triassic. It is important to point out that Lower Triassic deposits are quite rare in Argentina. Therefore, an alternative scenario cannot be dismissed, with stereospondyls colonizing the Argentinean Gondwana still during Early or Middle Triassic. Unfortunately, the small amount of information regarding the Lower Triassic in Argentina is an obstacle to clarify the sequence of events related to the diversification of stereospondyls in this part of Gondwana. Besides, to the present, there is no record of stereospondyls in Middle Triassic deposits from both Argentina and Brazil. Alternative explanations for their absence in the Middle Triassic of South America are either taphonomic bias or insufficient prospecting in deposits of this age. Stereospondyls (and other aquatic animals), tend to be less represented than other vertebrate groups, due to taphonomic bias, because the fluvial style causes a direct impact on the taphonomic mode of preservation. According to Fonseca and Scherer (1998) and Pires et al. (2005) the Triassic was marked by a large degree of seasonality, with large dry periods replaced by shorter periods of humidity. The increasing of humidity towards the top of the Triassic succession modified the fluvial environments from anastomosed to braided systems (Fonseca and Scherer, 1998). In braided systems, intense reworking tends to destroy delicate bones. Therefore, animals with slender skeletons (e. g. stereospondyls and phytosaurs) are likely to be less represented in this kind of depositional environment. In conclusion, further prospecting efforts are necessary in order to clarify the likely sequence of events related with the diversification of stereospondyls in South American Gondwana which would further contribute to our understanding of the evolution of West Gondwana (Vaughan and Pankhurst, 2008), as well as the paleobiogeography of crustal fragments in the erstwhile Gondwana assembly (cf. Meert and Lieberman, 2008). Acknowledgements SDS would like to thank the Universidade Federal do Pampa/UFSM, for the facilities provided during the present study, Claudia Marsicano for a critical review of an earlier version of this manuscript, Cristina Machado-Bertoni for her useful taphonomic insights, Juan Carlos Cisneros for the interpretative drawing of the Brazilian interclavicle (Fig. 3B), and Lúcia Helena do Canto Vinadé for English revision. In addition, we thank Jean Sébastien Steyer and an anonymous referee for their suggestions that greatly improved the manuscript. References Andreis, R., Bossi, G.E., Montardo, D.K., 1980. O Grupo Rosário do Sul (Triássico) no Rio Grande do Sul. 659–673. In: Monaco, O.A. (Ed.), Anais do XXXI Congresso Brasileiro de Geologia, Camboriú, Santa Catarina. Sociedade Brasileira de Geologia, São Paulo, Brazil, p. 1309.
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