Abstract - The record of non-mammaliaformes eucynodonts from the Carnian-Norian Ischigualasto Formation is diverse and abundant, including a medium to large size herbivore and small carnivores. Here is described a new small eucynodont from the Ischigualasto Formation, on the basis of a partial skull. The new taxon is characterized by palatal process of the premaxilla extending posterior to the level of the first postcanine; deep and large maxillary laterodorsal fossa that opens at the level of the root of the upper canine; and postorbital bar diverging posterolaterally at very low angle (35.6°) from the anteroposterior axis of the skull. Results from a phylogenetic analysis supports the new genus placement as a probainognathian eucynodont, more derived than Probainognathus Romer, and more closely related to Ecteninion Martinez, May & Forster and Trucidocynodon Oliveira, Soares & Schultz than to any other eucynodont. Ecteniniidae is proposed as a new clade including the new genus, Ecteninion and Trucidocynodon, and in the phylogenetic hypothesis represents the sister-group of Prozostrodontia (Prozostrodon Bonaparte & Barberena, Tritylodontidae and Mammaliaformes). Additionally, the new taxon from the Ischigualasto Formation shows that the Scaphonyx-Exaeretodon-Herrerasaurus biozone has similar cynodont diversity than the supposedly contemporaneous Hyperodapedon Assemblage Zone of Santa Maria 2 Sequence, in Southern Brazil.
Field of Science
A New Non-mammaliaform Eucynodont from the Ischigualasto Formation of Argentina
Martínez, R. N., Eliana Fernandez, E., and O. A. Alcober. 2013. A new non-mammaliaform eucynodont from the Carnian-Norian Ischigualasto Formation, Northwestern Argentina. Revista Brasileira de Paleontologia 16: 61-76. doi:10.4072/rbp.2013.1.05
Abstract - The record of non-mammaliaformes eucynodonts from the Carnian-Norian Ischigualasto Formation is diverse and abundant, including a medium to large size herbivore and small carnivores. Here is described a new small eucynodont from the Ischigualasto Formation, on the basis of a partial skull. The new taxon is characterized by palatal process of the premaxilla extending posterior to the level of the first postcanine; deep and large maxillary laterodorsal fossa that opens at the level of the root of the upper canine; and postorbital bar diverging posterolaterally at very low angle (35.6°) from the anteroposterior axis of the skull. Results from a phylogenetic analysis supports the new genus placement as a probainognathian eucynodont, more derived than Probainognathus Romer, and more closely related to Ecteninion Martinez, May & Forster and Trucidocynodon Oliveira, Soares & Schultz than to any other eucynodont. Ecteniniidae is proposed as a new clade including the new genus, Ecteninion and Trucidocynodon, and in the phylogenetic hypothesis represents the sister-group of Prozostrodontia (Prozostrodon Bonaparte & Barberena, Tritylodontidae and Mammaliaformes). Additionally, the new taxon from the Ischigualasto Formation shows that the Scaphonyx-Exaeretodon-Herrerasaurus biozone has similar cynodont diversity than the supposedly contemporaneous Hyperodapedon Assemblage Zone of Santa Maria 2 Sequence, in Southern Brazil.
Abstract - The record of non-mammaliaformes eucynodonts from the Carnian-Norian Ischigualasto Formation is diverse and abundant, including a medium to large size herbivore and small carnivores. Here is described a new small eucynodont from the Ischigualasto Formation, on the basis of a partial skull. The new taxon is characterized by palatal process of the premaxilla extending posterior to the level of the first postcanine; deep and large maxillary laterodorsal fossa that opens at the level of the root of the upper canine; and postorbital bar diverging posterolaterally at very low angle (35.6°) from the anteroposterior axis of the skull. Results from a phylogenetic analysis supports the new genus placement as a probainognathian eucynodont, more derived than Probainognathus Romer, and more closely related to Ecteninion Martinez, May & Forster and Trucidocynodon Oliveira, Soares & Schultz than to any other eucynodont. Ecteniniidae is proposed as a new clade including the new genus, Ecteninion and Trucidocynodon, and in the phylogenetic hypothesis represents the sister-group of Prozostrodontia (Prozostrodon Bonaparte & Barberena, Tritylodontidae and Mammaliaformes). Additionally, the new taxon from the Ischigualasto Formation shows that the Scaphonyx-Exaeretodon-Herrerasaurus biozone has similar cynodont diversity than the supposedly contemporaneous Hyperodapedon Assemblage Zone of Santa Maria 2 Sequence, in Southern Brazil.
Osteoderm Microstructure of “Rauisuchian” Archosaurs from South America
Cerda, I. A., J. B. Desojo, T. M. Scheyer and C. L. Schultz. In Press. Osteoderm microstructure of “rauisuchian” archosaurs from South America. Geobios (accepted manuscript) doi: http://dx.doi.org/10.1016/j.
Abstract - In this contribution we analyze and discuss the microanatomy and histology of postcranial osteoderms of a number of “rauisuchians” from different localities of South America (Argentina and Brazil). The studied sample includes osteoderms of Fasolasuchus tenax, Prestosuchus chiniquensis, Saurosuchus galilei and an undetermined rauisuchian from Brazil. The bone microanatomy of the osteoderms is variable: whereas some specimens have a rather compact structure, others show a diploe architecture with a central cancellous core bordered by two compact cortices. Both external and basal cortices are mainly composed of poorly vascularized, fine and coarse parallel fibred bone and networks of interwoven and mineralized fiber bundles. The internal region of the non-remodeled specimens consists of a well-vascularized core in which the intrinsic fibers exhibit important variations (even in the same specimen), ranging from coarse, parallel-fibred to woven-fibred bone tissues. Lines of arrested growth (LAGs) are well recorded in both basal and external cortices. Differences in the bone microstructure (compact vs. diploe) could be related to the age, sex and reproductive status of the sampled individuals. Hence, age estimation based on the count of LAGs in rauisuchian osteoderms appears to be reliable only in the early stages of ontogeny. The bone microstructure suggests that rauisuchian osteoderms were originated through a mechanism that involves both intramembranous and metaplastic ossifications.
Abstract - In this contribution we analyze and discuss the microanatomy and histology of postcranial osteoderms of a number of “rauisuchians” from different localities of South America (Argentina and Brazil). The studied sample includes osteoderms of Fasolasuchus tenax, Prestosuchus chiniquensis, Saurosuchus galilei and an undetermined rauisuchian from Brazil. The bone microanatomy of the osteoderms is variable: whereas some specimens have a rather compact structure, others show a diploe architecture with a central cancellous core bordered by two compact cortices. Both external and basal cortices are mainly composed of poorly vascularized, fine and coarse parallel fibred bone and networks of interwoven and mineralized fiber bundles. The internal region of the non-remodeled specimens consists of a well-vascularized core in which the intrinsic fibers exhibit important variations (even in the same specimen), ranging from coarse, parallel-fibred to woven-fibred bone tissues. Lines of arrested growth (LAGs) are well recorded in both basal and external cortices. Differences in the bone microstructure (compact vs. diploe) could be related to the age, sex and reproductive status of the sampled individuals. Hence, age estimation based on the count of LAGs in rauisuchian osteoderms appears to be reliable only in the early stages of ontogeny. The bone microstructure suggests that rauisuchian osteoderms were originated through a mechanism that involves both intramembranous and metaplastic ossifications.
Provincialization of Terrestrial Faunas Following the End-Permian Mass Extinction.
Sidor, C. A., D. A. Vilhena, K. D. Angielczyk, A. K. Huttenlocker, S. J. Nesbitt, B. R. Peecook, J. S. Steyer, R. M. H. Smith, and L. A. Tsuji. 2013. Provincialization of terrestrial faunas following the end-Permian mass extinction. Proceedings of the National Academy of Sciences (advance online publication)
doi: 10.1073/pnas.1302323110
Abstract - In addition to their devastating effects on global biodiversity, mass extinctions have had a long-term influence on the history of life by eliminating dominant lineages that suppressed ecological change. Here, we test whether the end-Permian mass extinction (252.3 Ma) affected the distribution of tetrapod faunas within the southern hemisphere and apply quantitative methods to analyze four components of biogeographic structure: connectedness, clustering, range size, and endemism. For all four components, we detected increased provincialism between our Permian and Triassic datasets. In southern Pangea, a more homogeneous and broadly distributed fauna in the Late Permian (Wuchiapingian, ~257 Ma) was replaced by a provincial and biogeographically fragmented fauna by Middle Triassic times (Anisian, ~242 Ma). Importantly in the Triassic, lower latitude basins in Tanzania and Zambia included dinosaur predecessors and other archosaurs unknown elsewhere. The recognition of heterogeneous tetrapod communities in the Triassic implies that the end-Permian mass extinction afforded ecologically marginalized lineages the ecospace to diversify, and that biotic controls (i.e., evolutionary incumbency) were fundamentally reset. Archosaurs, which began diversifying in the Early Triassic, were likely beneficiaries of this ecological release and remained dominant for much of the later Mesozoic.
doi: 10.1073/pnas.1302323110
Abstract - In addition to their devastating effects on global biodiversity, mass extinctions have had a long-term influence on the history of life by eliminating dominant lineages that suppressed ecological change. Here, we test whether the end-Permian mass extinction (252.3 Ma) affected the distribution of tetrapod faunas within the southern hemisphere and apply quantitative methods to analyze four components of biogeographic structure: connectedness, clustering, range size, and endemism. For all four components, we detected increased provincialism between our Permian and Triassic datasets. In southern Pangea, a more homogeneous and broadly distributed fauna in the Late Permian (Wuchiapingian, ~257 Ma) was replaced by a provincial and biogeographically fragmented fauna by Middle Triassic times (Anisian, ~242 Ma). Importantly in the Triassic, lower latitude basins in Tanzania and Zambia included dinosaur predecessors and other archosaurs unknown elsewhere. The recognition of heterogeneous tetrapod communities in the Triassic implies that the end-Permian mass extinction afforded ecologically marginalized lineages the ecospace to diversify, and that biotic controls (i.e., evolutionary incumbency) were fundamentally reset. Archosaurs, which began diversifying in the Early Triassic, were likely beneficiaries of this ecological release and remained dominant for much of the later Mesozoic.
Overview of the Triassic Pterosaur Record
Another paper from the upcoming volume on Triassic archosaurs.
Dalla Vecchia, F. 2013. Triassic Pterosaurs. From Nesbitt, S. J., Desojo, J. B. & Irmis, R. B. (eds) 2013. Anatomy, Phylogeny and Palaeobiology of Early Archosaurs and their Kin. Geological Society, London, Special Publications, 379, http://dx.doi.org/10.1144/SP379.14
Abstract - Pterosaurs are a clade of highly specialized, volant archosauromorphs recorded from the Upper Triassic to the uppermost Cretaceous. Problematic remains referred to the Pterosauria are reported from the Triassic of Europe and both North and South America, but unequivocal pterosaur specimens are only known from the Alps (Italy, Austria and Switzerland: Preondactylus buffarinii, Austriadactylus cristatus, Peteinosaurus zambellii, Eudimorphodon ranzii, Carniadactylus rosenfeldi, Caviramus schesaplanensis and Raeticodactylus filisurensis) and Greenland (‘Eudimorphodon’ cromptonellus). Pterosaurs are diagnosed mostly by features associated with the advent of powered flight. They are generally considered to be archosaurians more closely related to dinosaurs than to crocodilians, but non-archosaurian positions have also been proposed. There is a lack of general agreement about ingroup relationships, particularly among the basal pterosaurs. Triassic pterosaurs differ from other non-pterodactyloid pterosaurs in features of the dentition and caudal vertebral column. A ‘Big Bang’ model for their early history fits better with the fossil record: the earliest unequivocal pterosaurs show a sudden and geographically limited appearance in the fossil record, as well as a relatively high burst of diversity and considerable morphologic disparity. Absence of pterosaur remains from deposits where they are expected to be found suggests that they had not yet evolved in pre-Norian times.
Dalla Vecchia, F. 2013. Triassic Pterosaurs. From Nesbitt, S. J., Desojo, J. B. & Irmis, R. B. (eds) 2013. Anatomy, Phylogeny and Palaeobiology of Early Archosaurs and their Kin. Geological Society, London, Special Publications, 379, http://dx.doi.org/10.1144/SP379.14
Abstract - Pterosaurs are a clade of highly specialized, volant archosauromorphs recorded from the Upper Triassic to the uppermost Cretaceous. Problematic remains referred to the Pterosauria are reported from the Triassic of Europe and both North and South America, but unequivocal pterosaur specimens are only known from the Alps (Italy, Austria and Switzerland: Preondactylus buffarinii, Austriadactylus cristatus, Peteinosaurus zambellii, Eudimorphodon ranzii, Carniadactylus rosenfeldi, Caviramus schesaplanensis and Raeticodactylus filisurensis) and Greenland (‘Eudimorphodon’ cromptonellus). Pterosaurs are diagnosed mostly by features associated with the advent of powered flight. They are generally considered to be archosaurians more closely related to dinosaurs than to crocodilians, but non-archosaurian positions have also been proposed. There is a lack of general agreement about ingroup relationships, particularly among the basal pterosaurs. Triassic pterosaurs differ from other non-pterodactyloid pterosaurs in features of the dentition and caudal vertebral column. A ‘Big Bang’ model for their early history fits better with the fossil record: the earliest unequivocal pterosaurs show a sudden and geographically limited appearance in the fossil record, as well as a relatively high burst of diversity and considerable morphologic disparity. Absence of pterosaur remains from deposits where they are expected to be found suggests that they had not yet evolved in pre-Norian times.
Six New Papers from the Forthcoming Volume 'Anatomy, Phylogeny, and Palaeobiology of Early Archosaurs and their Kin.
You can access the abstracts electronically here.
Mastrantonio, B. M., Schultz, C. L., Desojo, J. B., and J. Bittencourt Garcia. 2013. The braincase of Prestosuchus chiniquensis (Archosauria: Suchia)From: Nesbitt, S. J., Desojo, J. B. & Irmis, R. B. (eds) 2013. Anatomy, Phylogeny and Palaeobiology of Early Archosaurs and their Kin. Geological Society, London, Special Publications, 379, doi:10.1144/SP379.10
Abstract - The osteology of an almost complete braincase of the rauisuchian archosaurs Prestosuchus chiniquensis from the Middle Triassic of Brazil is described for first time, based on two specimens (UFRGS-PV-0629-T and UFRGS-PV-0156-T). A comparative description with other taxa of rauisuchians is presented that forms the basis of a phylogenetic analysis. To perform the phylogenetic analysis, we describe and discuss each character codification for a modified version of the recent matrices of Gower (2002), Gower & Nesbitt (2006) and Brusatte et al.(2010). The analysis resulted in two most parsimonious trees that differ from the topologies recovered by Gower (2002) in a few aspects within Rauisuchia, and Prestosuchus chiniquensis was unequivocally depicted as deeply nested within Pseudosuchia, as the sister taxon of Batrachotomus kuperferzellensis in both topologies, supported by a single synapomorphy: the reduced to small fissure of the post-temporal fenestra between parietal, supraoccipital and exoccipital-opisthotic.
Sues, H.-D., Desojo, J. B., and M. D. Ezcurra. 2013. Doswelliidae: a clade of unusual armoured archosauriforms from the Middle and Late Triassic. From: Nesbitt, S. J., Desojo, J. B. & Irmis, R. B. (eds) 2013. Anatomy, Phylogeny and Palaeobiology of Early Archosaurs and their Kin. Geological Society, London, Special Publications, 379, first published on April 23, 2013, doi:10.1144/SP379.13
Abstract - Doswelliidae is a clade of armoured non-archosaurian archosauriform reptiles more closely related to Archosauria than are Proterosuchidae, Erythrosuchidae and possibly Euparkeria capensis. It is currently known from the late Middle Triassic (Ladinian) of Germany, the late Middle to early Late Triassic (Ladinian–Carnian) of Argentina and Brazil, and the Late Triassic (Carnian–Norian) of the USA. To date, two unambiguous synapomorphies diagnose Doswelliidae: (i) osteoderm ornamentation coarse, incised, and composed of central regular pits of subequal size and shape, and (ii) osteoderms with anterior articular lamina. Five taxa are currently recognized: Archeopelta arborensis, Doswellia kaltenbachi, Doswellia sixmilensis, Tarjadia ruthae and a new taxon from Germany. Based on skeletal features and occurrence, doswelliid archosauriforms may have had a semi-aquatic mode of life.
Langer, M. C., and J. Ferigolo. 2013. The Late Triassic dinosauromorph Sacisaurus agudoensis (Caturrita Formation; Rio Grande do Sul, Brazil): anatomy and affinities. From: Nesbitt, S. J., Desojo, J. B. & Irmis, R. B. (eds) 2013. Anatomy, Phylogeny and Palaeobiology of Early Archosaurs and their Kin. Geological Society, London, Special Publications, 379, first published on April 23, 2013, doi:10.1144/SP379.16
Abstract - Silesauridae is an exclusively Triassic group of dinosauromorphs, knowledge on the diversity of which has increased dramatically in the last few years. Silesaurid relationships are still contentious, as a result in part of different homology statements, particularly regarding the typical edentulous mandible tip of these animals. One of the most complete silesaurids yet discovered is Sacisaurus agudoensis from the Caturrita Formation (Late Triassic: Norian) of Rio Grande do Sul, Brazil, represented by numerous isolated bones recovered from a single site. The anatomy of S. agudoensis is fully described for the first time here, and comparisons are provided to other basal dinosauromorphs. S. agudoensis is a small-bodied animal (less than 1 m in length) that possesses a dentition consisting of leaf-shaped crowns with large denticles in the carinae, a plesiomorphic propubic pelvis with an almost fully closed acetabulum, elongate distal hindlimbs suggesting well-developed cursorial ability, and a laterally projected outer malleolus in the tibia. All previous numerical phylogenies supported a non-dinosaur dinosauromorph affinity for Silesauridae, but the reanalysis of one of those studies suggests that a position within Dinosauria is not unlikely, with silesaurids forming the basal branch of the ornithischian lineage.
Turner, A. H., and S. J. Nesbitt. 2013. Body size evolution during the Triassic archosauriform radiation. From: Nesbitt, S. J., Desojo, J. B. & Irmis, R. B. (eds) 2013. Anatomy, Phylogeny and Palaeobiology of Early Archosaurs and their Kin. Geological Society, London, Special Publications, 379, first published on April 23, 2013, doi:10.1144/SP379.15
Abstract - The first large (>1 m) diapsids appeared near the Permian–Triassic extinction and a subset of diapsids, the archosauriforms, expanded their body size range soon after in the Early–Middle Triassic. Here, we examine body size at key evolutionary events within Archosauriformes during the Triassic and through the end-Triassic extinction. Using femoral length as a body size proxy and a temporally calibrated phylogeny of Archosauriformes, we estimate ancestral body sizes using a maximum likelihood approach and test for the presence of an adapative radiation by comparing the fit of competing evolutionary models. Archosauriform body size is characterized by punctuated change with more change occurring early in the Triassic. Archosaurs crossing the Triassic–Jurassic boundary show a wide range in ancestral size, and dinosaurs (sauropodomorphs and theropods) are considerably larger in the Jurassic. Crocodylomorph origins are characterized by a drop in body size; however, both the relative amount of change and the rate of change are matched among other archosaur clades. Archosauriforms increase in absolute body size through the Triassic and evidence suggests that a directional trend in size increase occurred in the early Mesozoic. The morphological signature of adaptive radiation is rare in comparative data from extant animals but is present at the origination of Archosauriformes.
Niedźwiedzki, G., Brusatte, S. L., and R. J. Butler. 2013. Prorotodactylus and Rotodactylus tracks: an ichnological record of dinosauromorphs from the Early–Middle Triassic of Poland. From: Nesbitt, S. J., Desojo, J. B. & Irmis, R. B. (eds) 2013. Anatomy, Phylogeny and Palaeobiology of Early Archosaurs and their Kin. Geological Society, London, Special Publications, 379, first published on April 23, 2013, doi:10.1144/SP379.12
Abstract - We present the first comprehensive description of Prorotodactylus and Rotodactylus dinosauromorph tracks from the Early and Middle Triassic of the Holy Cross Mountains, Poland. We describe and comprehensively figure tracks that have been mentioned briefly in previous accounts as well as new, recently discovered material, and analyse the variation and stratigraphic distribution of these specimens. Tracks have been recorded from four sites – Koszary, Stryczowice, Wióry and Baranów – which span the early Olenekian – early Anisian (c.250–246 Ma). These tracks therefore represent an ichnological record of the evolutionary succession of early dinosauromorphs during the earliest part of their evolutionary history. Recognized track types include cf. Prorotodactylus isp., Prorotodactylus isp., Prorotodactylus mirus, Rotodactylus cursorius, Rotodactylus isp. and cf. Rotodactylus isp. At least three distinct Early and early Middle Triassic early dinosauromorph ichnofaunas can be recognized. The oldest, which is early Olenekian in age, is characterized by the presence of Prorotodactylus isp., cf.Prorotodactylus isp. and non-archosaurian archosauromorph or archosaur tracks (e.g. Synaptichnium isp., Protochirotherium isp.), recorded at the Stryczowice and Koszary sites. The following assemblage, recorded at the late Olenekian Wióry site, displays the highest ichnodiversity of dinosauromorphs, with four track types present (Prorotodactylus isp., Prorotodactylus mirus, Rotodactylus cursorius and cf. Rotodactylus isp.). The youngest site, Baranów, includes Rotodactylus isp., as well as other larger dinosauromorph tracks. The first body fossil evidence of dinosauromorphs is a few million years younger than the youngest Polish tracks, so Prorotodactylus and Rotodactylus tracks currently provide the oldest record of dinosauromorph morphology, biology and evolution.
Ezcurra, M. D., Butler, R. J., and D. J. Gower. 2013. ‘Proterosuchia’: the origin and early history of Archosauriformes.. From: Nesbitt, S. J., Desojo, J. B. & Irmis, R. B. (eds) 2013. Anatomy, Phylogeny and Palaeobiology of Early Archosaurs and their Kin. Geological Society, London, Special Publications, 379, first published on April 23, 2013, doi:10.1144/SP379.11
Abstract - The earliest history of Archosauriformes is mainly represented by members of Proterosuchidae and Erythrosuchidae, which are known worldwide from latest Permian to Middle Triassic beds. These two groups were historically combined within ‘Proterosuchia’, with approximately 30 nominal species. Two morphotypes have been recognized among proterosuchians: proterosuchids with a generally more sprawling gait and elongated and low skulls with an overhanging premaxilla, and the more heavily built erythrosuchids, with a probably less sprawling gait and large, presumably hypercarnivorous, skulls. The systematics of ‘Proterosuchia’ was relatively chaotic throughout most of the twentieth century, but currently there exists consensus regarding the non-monophyly of proterosuchians and their phylogenetic position outside all other archosauriforms. In contrast, the delimitation and taxonomic content of Proterosuchidae and Erythrosuchidae remain unstable. Few studies of proterosuchian palaeobiology have been carried out. Current lines of evidence favour a predominantly terrestrial lifestyle for proterosuchians. Limb bone histology indicates rapid continuous growth rates in Proterosuchus and Erythrosuchus before reaching sexual maturity. A better knowledge of proterosuchian anatomy, systematics, evolution and ecology is important for advancing understanding of the origin and early radiation of Archosauriformes and the patterns of biotic recovery following the Permo-Triassic mass extinction event. There remains much research to be carried out in proterosuchian palaeobiology.
Mastrantonio, B. M., Schultz, C. L., Desojo, J. B., and J. Bittencourt Garcia. 2013. The braincase of Prestosuchus chiniquensis (Archosauria: Suchia)From: Nesbitt, S. J., Desojo, J. B. & Irmis, R. B. (eds) 2013. Anatomy, Phylogeny and Palaeobiology of Early Archosaurs and their Kin. Geological Society, London, Special Publications, 379, doi:10.1144/SP379.10
Abstract - The osteology of an almost complete braincase of the rauisuchian archosaurs Prestosuchus chiniquensis from the Middle Triassic of Brazil is described for first time, based on two specimens (UFRGS-PV-0629-T and UFRGS-PV-0156-T). A comparative description with other taxa of rauisuchians is presented that forms the basis of a phylogenetic analysis. To perform the phylogenetic analysis, we describe and discuss each character codification for a modified version of the recent matrices of Gower (2002), Gower & Nesbitt (2006) and Brusatte et al.(2010). The analysis resulted in two most parsimonious trees that differ from the topologies recovered by Gower (2002) in a few aspects within Rauisuchia, and Prestosuchus chiniquensis was unequivocally depicted as deeply nested within Pseudosuchia, as the sister taxon of Batrachotomus kuperferzellensis in both topologies, supported by a single synapomorphy: the reduced to small fissure of the post-temporal fenestra between parietal, supraoccipital and exoccipital-opisthotic.
Sues, H.-D., Desojo, J. B., and M. D. Ezcurra. 2013. Doswelliidae: a clade of unusual armoured archosauriforms from the Middle and Late Triassic. From: Nesbitt, S. J., Desojo, J. B. & Irmis, R. B. (eds) 2013. Anatomy, Phylogeny and Palaeobiology of Early Archosaurs and their Kin. Geological Society, London, Special Publications, 379, first published on April 23, 2013, doi:10.1144/SP379.13
Abstract - Doswelliidae is a clade of armoured non-archosaurian archosauriform reptiles more closely related to Archosauria than are Proterosuchidae, Erythrosuchidae and possibly Euparkeria capensis. It is currently known from the late Middle Triassic (Ladinian) of Germany, the late Middle to early Late Triassic (Ladinian–Carnian) of Argentina and Brazil, and the Late Triassic (Carnian–Norian) of the USA. To date, two unambiguous synapomorphies diagnose Doswelliidae: (i) osteoderm ornamentation coarse, incised, and composed of central regular pits of subequal size and shape, and (ii) osteoderms with anterior articular lamina. Five taxa are currently recognized: Archeopelta arborensis, Doswellia kaltenbachi, Doswellia sixmilensis, Tarjadia ruthae and a new taxon from Germany. Based on skeletal features and occurrence, doswelliid archosauriforms may have had a semi-aquatic mode of life.
Langer, M. C., and J. Ferigolo. 2013. The Late Triassic dinosauromorph Sacisaurus agudoensis (Caturrita Formation; Rio Grande do Sul, Brazil): anatomy and affinities. From: Nesbitt, S. J., Desojo, J. B. & Irmis, R. B. (eds) 2013. Anatomy, Phylogeny and Palaeobiology of Early Archosaurs and their Kin. Geological Society, London, Special Publications, 379, first published on April 23, 2013, doi:10.1144/SP379.16
Abstract - Silesauridae is an exclusively Triassic group of dinosauromorphs, knowledge on the diversity of which has increased dramatically in the last few years. Silesaurid relationships are still contentious, as a result in part of different homology statements, particularly regarding the typical edentulous mandible tip of these animals. One of the most complete silesaurids yet discovered is Sacisaurus agudoensis from the Caturrita Formation (Late Triassic: Norian) of Rio Grande do Sul, Brazil, represented by numerous isolated bones recovered from a single site. The anatomy of S. agudoensis is fully described for the first time here, and comparisons are provided to other basal dinosauromorphs. S. agudoensis is a small-bodied animal (less than 1 m in length) that possesses a dentition consisting of leaf-shaped crowns with large denticles in the carinae, a plesiomorphic propubic pelvis with an almost fully closed acetabulum, elongate distal hindlimbs suggesting well-developed cursorial ability, and a laterally projected outer malleolus in the tibia. All previous numerical phylogenies supported a non-dinosaur dinosauromorph affinity for Silesauridae, but the reanalysis of one of those studies suggests that a position within Dinosauria is not unlikely, with silesaurids forming the basal branch of the ornithischian lineage.
Turner, A. H., and S. J. Nesbitt. 2013. Body size evolution during the Triassic archosauriform radiation. From: Nesbitt, S. J., Desojo, J. B. & Irmis, R. B. (eds) 2013. Anatomy, Phylogeny and Palaeobiology of Early Archosaurs and their Kin. Geological Society, London, Special Publications, 379, first published on April 23, 2013, doi:10.1144/SP379.15
Abstract - The first large (>1 m) diapsids appeared near the Permian–Triassic extinction and a subset of diapsids, the archosauriforms, expanded their body size range soon after in the Early–Middle Triassic. Here, we examine body size at key evolutionary events within Archosauriformes during the Triassic and through the end-Triassic extinction. Using femoral length as a body size proxy and a temporally calibrated phylogeny of Archosauriformes, we estimate ancestral body sizes using a maximum likelihood approach and test for the presence of an adapative radiation by comparing the fit of competing evolutionary models. Archosauriform body size is characterized by punctuated change with more change occurring early in the Triassic. Archosaurs crossing the Triassic–Jurassic boundary show a wide range in ancestral size, and dinosaurs (sauropodomorphs and theropods) are considerably larger in the Jurassic. Crocodylomorph origins are characterized by a drop in body size; however, both the relative amount of change and the rate of change are matched among other archosaur clades. Archosauriforms increase in absolute body size through the Triassic and evidence suggests that a directional trend in size increase occurred in the early Mesozoic. The morphological signature of adaptive radiation is rare in comparative data from extant animals but is present at the origination of Archosauriformes.
Niedźwiedzki, G., Brusatte, S. L., and R. J. Butler. 2013. Prorotodactylus and Rotodactylus tracks: an ichnological record of dinosauromorphs from the Early–Middle Triassic of Poland. From: Nesbitt, S. J., Desojo, J. B. & Irmis, R. B. (eds) 2013. Anatomy, Phylogeny and Palaeobiology of Early Archosaurs and their Kin. Geological Society, London, Special Publications, 379, first published on April 23, 2013, doi:10.1144/SP379.12
Abstract - We present the first comprehensive description of Prorotodactylus and Rotodactylus dinosauromorph tracks from the Early and Middle Triassic of the Holy Cross Mountains, Poland. We describe and comprehensively figure tracks that have been mentioned briefly in previous accounts as well as new, recently discovered material, and analyse the variation and stratigraphic distribution of these specimens. Tracks have been recorded from four sites – Koszary, Stryczowice, Wióry and Baranów – which span the early Olenekian – early Anisian (c.250–246 Ma). These tracks therefore represent an ichnological record of the evolutionary succession of early dinosauromorphs during the earliest part of their evolutionary history. Recognized track types include cf. Prorotodactylus isp., Prorotodactylus isp., Prorotodactylus mirus, Rotodactylus cursorius, Rotodactylus isp. and cf. Rotodactylus isp. At least three distinct Early and early Middle Triassic early dinosauromorph ichnofaunas can be recognized. The oldest, which is early Olenekian in age, is characterized by the presence of Prorotodactylus isp., cf.Prorotodactylus isp. and non-archosaurian archosauromorph or archosaur tracks (e.g. Synaptichnium isp., Protochirotherium isp.), recorded at the Stryczowice and Koszary sites. The following assemblage, recorded at the late Olenekian Wióry site, displays the highest ichnodiversity of dinosauromorphs, with four track types present (Prorotodactylus isp., Prorotodactylus mirus, Rotodactylus cursorius and cf. Rotodactylus isp.). The youngest site, Baranów, includes Rotodactylus isp., as well as other larger dinosauromorph tracks. The first body fossil evidence of dinosauromorphs is a few million years younger than the youngest Polish tracks, so Prorotodactylus and Rotodactylus tracks currently provide the oldest record of dinosauromorph morphology, biology and evolution.
Ezcurra, M. D., Butler, R. J., and D. J. Gower. 2013. ‘Proterosuchia’: the origin and early history of Archosauriformes.. From: Nesbitt, S. J., Desojo, J. B. & Irmis, R. B. (eds) 2013. Anatomy, Phylogeny and Palaeobiology of Early Archosaurs and their Kin. Geological Society, London, Special Publications, 379, first published on April 23, 2013, doi:10.1144/SP379.11
Abstract - The earliest history of Archosauriformes is mainly represented by members of Proterosuchidae and Erythrosuchidae, which are known worldwide from latest Permian to Middle Triassic beds. These two groups were historically combined within ‘Proterosuchia’, with approximately 30 nominal species. Two morphotypes have been recognized among proterosuchians: proterosuchids with a generally more sprawling gait and elongated and low skulls with an overhanging premaxilla, and the more heavily built erythrosuchids, with a probably less sprawling gait and large, presumably hypercarnivorous, skulls. The systematics of ‘Proterosuchia’ was relatively chaotic throughout most of the twentieth century, but currently there exists consensus regarding the non-monophyly of proterosuchians and their phylogenetic position outside all other archosauriforms. In contrast, the delimitation and taxonomic content of Proterosuchidae and Erythrosuchidae remain unstable. Few studies of proterosuchian palaeobiology have been carried out. Current lines of evidence favour a predominantly terrestrial lifestyle for proterosuchians. Limb bone histology indicates rapid continuous growth rates in Proterosuchus and Erythrosuchus before reaching sexual maturity. A better knowledge of proterosuchian anatomy, systematics, evolution and ecology is important for advancing understanding of the origin and early radiation of Archosauriformes and the patterns of biotic recovery following the Permo-Triassic mass extinction event. There remains much research to be carried out in proterosuchian palaeobiology.
A new interpretation of material of an armored archosauriform from the Middle Triassic of Germany that solves the mystery of the purported Middle Triassic aetosaur. Instead this specimen is from a taxon more closely to Doswellia kaltenbachi. This new taxon supports the growing realization that doswelliids had a broader range geographically and temporally.
Schoch, R. R., and H.-D. Sues. 2013. A new archosauriform reptile from the Middle Triassic (Ladinian) of Germany. Journal of Systematic Palaeontology (advance online publication) DOI:10.1080/14772019.2013.781066
Abstract- Numerous well-preserved skeletal remains of a distinctive armoured archosauriform reptile from the Lower Keuper (Erfurt Formation; Middle Triassic: Ladinian: Longobardian) of Baden-Württemberg (Germany) represent a new taxon, Jaxtasuchus salomoni gen. et sp. nov. The dermal armour of Jaxtasuchus comprises transverse rows of four rectangular osteoderms each in the cervical, dorsal and caudal regions, with the individual plates closely resembling those of Doswellia kaltenbachi from Carnian strata in North America. The long and low maxilla of Jaxtasuchus held at least 15 teeth. The labial and lingual surfaces of the tall, only slightly recurved crowns of the maxillary teeth bear distinct vertical ridges and smooth mesial and distal carinae. The cervical region of the vertebral column is long. Phylogenetic analysis places Jaxtasuchus as the sister taxon to
Doswellia in Doswelliidae sensu Desojo et al. (2011). Doswelliidae is diagnosed by the coarsely reticulate, incised ornamentation of osteoderms composed of central regular pits of subequal size and contour, and a mostly smooth anterior articular lamina on each osteoderm. The discovery of Jaxtasuchus confirms that Doswelliidae had a wide palaeogeographical distribution during the latter half of the Triassic.
Schoch, R. R., and H.-D. Sues. 2013. A new archosauriform reptile from the Middle Triassic (Ladinian) of Germany. Journal of Systematic Palaeontology (advance online publication) DOI:10.1080/14772019.2013.781066
Abstract- Numerous well-preserved skeletal remains of a distinctive armoured archosauriform reptile from the Lower Keuper (Erfurt Formation; Middle Triassic: Ladinian: Longobardian) of Baden-Württemberg (Germany) represent a new taxon, Jaxtasuchus salomoni gen. et sp. nov. The dermal armour of Jaxtasuchus comprises transverse rows of four rectangular osteoderms each in the cervical, dorsal and caudal regions, with the individual plates closely resembling those of Doswellia kaltenbachi from Carnian strata in North America. The long and low maxilla of Jaxtasuchus held at least 15 teeth. The labial and lingual surfaces of the tall, only slightly recurved crowns of the maxillary teeth bear distinct vertical ridges and smooth mesial and distal carinae. The cervical region of the vertebral column is long. Phylogenetic analysis places Jaxtasuchus as the sister taxon to
Doswellia in Doswelliidae sensu Desojo et al. (2011). Doswelliidae is diagnosed by the coarsely reticulate, incised ornamentation of osteoderms composed of central regular pits of subequal size and contour, and a mostly smooth anterior articular lamina on each osteoderm. The discovery of Jaxtasuchus confirms that Doswelliidae had a wide palaeogeographical distribution during the latter half of the Triassic.
Morphology and Diversity of the Mandibular Symphysis of Archosauriforms
Excellent study that demonstrates changes in mandibular symphyses through individual clades; changes that appear to be influenced by changes in dental morphology, which presumably reflect differences in diet. This paper is part of the upcoming volume on early archosaurs.
Abstract: Archosauromorphs
radiated into numerous trophic niches during the Mesozoic, many of which were
accommodated by particular suites of cranial adaptations and feeding
behaviours. The mandibular symphysis, the joint linking the mandibles, is a
poorly understood craniomandibular joint that may offer significant insight
into skull function and feeding ecology. Using comparative data from extant
amniotes, we investigated the skeletal anatomy and osteological correlates of relevant
soft tissues in a survey of archosauromorph mandibular symphyses. Characters
were identified and their evolution mapped using a current phylogeny of archosauriforms
with the addition of non-archosauriform archosauromorphs. Extinct taxa with the
simple Class I condition (e.g. proterochampsids, ‘rauisuchians’), rugose Class
II (aetosaurs, protosuchians, silesaurids) and interdigitating Class III
symphyses (e.g. phytosaurs, crocodyliforms) and finally fused Class IV (avians)
build the joints in expected ways, although they differ in the contributions of
bony elements and Meckel’s cartilage. Optimization of the different classes of
symphyses across archosauromorph clades indicates that major iterative
transitions from plesiomorphic Class I to derived, rigid Class II–IV symphyses
occurred along the lines to phytosaurs, aetosaurs, a subset of poposauroids, crocodyliformes,
pterosaurs and birds. These transitions in symphyseal morphology also appear to
track changes in dentition and potentially diet.
Holliday, C. M., and S. J. Nesbitt.
2013. Morphology and diversity of the mandibular symphysis of archosauriforms In Nesbitt, S. J., Desojo, J. B. and R.
B. Irmis (eds) Anatomy, Phylogeny and Palaeobiology of Early Archosaurs and
their Kin. Geological Society, London, Special Publications, 379, http://dx.doi.org/10.1144/SP379.2
New Occurrences of the Controversial Late Triassic Plant Fossil Sanmiguelia
New paper extending the biostratigraphic range of the enigmatic Late Triassic plant Sanmiguelia. These new finds also alter the plant-based biostratigraphic scheme proposed by Ash in 1980.
Ash,
S.R. and S. T. Hasiotis, S.T. 2013. New occurrences of the controversial Late
Triassic plant fossil Sanmiguelia Brown and associated ichnofossils in
the Chinle Formation of Arizona and Utah, USA. Neues Jahrbuch für Geologie und
Paläontologie Abhandlungen 268: 65–82.
Abstract:
Fragments
of the rare and distinctive palm-like leaves of the controversial Late Triassic
plant Sanmiguelia have been discovered recently in both Petrified Forest
National Park, Arizona and Arches National Park, Utah. Although, the new
specimens do not clarify the classification of this intriguing fossil, they do
confirm that it occurs in all members of the Chinle Formation except for the
very lowest units, the Shinarump, Mesa Redondo, and Temple Mountain members.
Furthermore, their discovery in Petrified Forest National Park extends the
known geographical distribution of the fossil into east-central Arizona and
demonstrates that it is a characteristic member of the Late Triassic flora of
the American southwest and requires a revision of the Chinle floral zone scheme
proposed and revised earlier by Ash (1980). In Petrified Forest National Park
the leaves are associated with several types of ichnofossils including Scoyenia,
Arenicolites, Cylindrichum, cf. Scolicia, cf. Beaconites,
Selenchnites, and other trace fossils in open nomenclature. These trace
fossils suggest that Sanmiguelia was preserved in high moisture,
imperfectly drained, water-margin setting inhabited by phytosaurs, snails,
horseshoe crabs, and a variety of arthropods such as beetles and dipteran
larvae and record high water table conditions punctuated by flooding and overbank
deposition. The findings reported here generally support and improve on
previous interpretations of the paleoenvironment inhabited by the Sanmiguelia
plant.
Triassic–Jurassic Mass Extinction as Trigger for the Mesozoic Radiation of Crocodylomorphs
A new study that contrasts that of Brusatte et al. (2008), who had found a significant dropoff in pseudosuchian disparity through the end Triassic extinction.
Toljagić, O., and R. J. Butler. 2013 Triassic–Jurassic mass extinction as trigger for the Mesozoic radiation of crocodylomorphs. Biology Letters 9: 20130095. http://dx.doi.org/10.1098/rsbl.2013.0095
Abstract - Pseudosuchia, one of the two main clades of Archosauria (Reptilia: Diapsida), suffered a major decline in lineage diversity during the Triassic–Jurassic (TJ) mass extinction (approx. 201 Ma). Crocodylomorpha, including living crocodilians and their extinct relatives, is the only group of pseudosuchians that survived into the Jurassic.We reassess changes in pseudosuchian morphological diversity (disparity) across this time interval, using considerably larger sample sizes than in previous analyses. Our results show that metrics of pseudosuchian disparity did not change significantly across the TJ boundary, contrasting with previous work suggesting low pseudosuchian disparity in the Early Jurassic following the TJ mass extinction. However, a significant shift in morphospace occupation between Late Triassic and Early Jurassic taxa is recognized, suggesting that the TJ extinction of many pseudosuchian lineages was followed by a major and geologically rapid adaptive radiation of crocodylomorphs. This marks the onset of the spectacularly successful evolutionary history of crocodylomorphs in Jurassic and Cretaceous ecosystems.
Toljagić, O., and R. J. Butler. 2013 Triassic–Jurassic mass extinction as trigger for the Mesozoic radiation of crocodylomorphs. Biology Letters 9: 20130095. http://dx.doi.org/10.1098/rsbl.2013.0095
Abstract - Pseudosuchia, one of the two main clades of Archosauria (Reptilia: Diapsida), suffered a major decline in lineage diversity during the Triassic–Jurassic (TJ) mass extinction (approx. 201 Ma). Crocodylomorpha, including living crocodilians and their extinct relatives, is the only group of pseudosuchians that survived into the Jurassic.We reassess changes in pseudosuchian morphological diversity (disparity) across this time interval, using considerably larger sample sizes than in previous analyses. Our results show that metrics of pseudosuchian disparity did not change significantly across the TJ boundary, contrasting with previous work suggesting low pseudosuchian disparity in the Early Jurassic following the TJ mass extinction. However, a significant shift in morphospace occupation between Late Triassic and Early Jurassic taxa is recognized, suggesting that the TJ extinction of many pseudosuchian lineages was followed by a major and geologically rapid adaptive radiation of crocodylomorphs. This marks the onset of the spectacularly successful evolutionary history of crocodylomorphs in Jurassic and Cretaceous ecosystems.
New Data Linking the End-Triassic Extinction with the Central Atlantic Magmatic Province.
Out today in Science Express. This study also provides support for the accuracy of the astrochronologically tuned time scale proposed for the Late Triassic Newark Supergroup sequence.
Blackburn, T. J., Olsen, P. E., Bowring, S. A., McLean, N. M., Kent, D. V., Puffer, J., McHone, G., Rasbury, E. T., and M. Et-Touhami. 2013. Zircon U-Pb Geochronology Links the End-Triassic Extinction with the Central Atlantic Magmatic Province. Science Express. http://www.sciencemag.org/content/early/recent / 21 March 2013 / Page 1/ 10.1126/science.1234204
Abstract - The end-Triassic extinction is characterized by major losses in both terrestrial and marine diversity, setting the stage for dinosaurs to dominate Earth for the next 136 million years. Despite the approximate coincidence between this extinction and flood basalt volcanism, existing geochronologic dates have insufficient resolution to confirm eruptive rates required to induce major climate perturbations. Here we present new zircon U-Pb geochronologic constraints on the age and duration of flood basalt volcanism within the Central Atlantic Magmatic Province. This chronology demonstrates synchroneity between the earliest volcanism and extinction, tests and corroborates the existing astrochronologic time scale, and shows that the release of magma and associated atmospheric flux occurred in four pulses over ~600,000 years, indicating expansive volcanism even as the biologic recovery was under way.
Blackburn, T. J., Olsen, P. E., Bowring, S. A., McLean, N. M., Kent, D. V., Puffer, J., McHone, G., Rasbury, E. T., and M. Et-Touhami. 2013. Zircon U-Pb Geochronology Links the End-Triassic Extinction with the Central Atlantic Magmatic Province. Science Express. http://www.sciencemag.org/content/early/recent / 21 March 2013 / Page 1/ 10.1126/science.1234204
Abstract - The end-Triassic extinction is characterized by major losses in both terrestrial and marine diversity, setting the stage for dinosaurs to dominate Earth for the next 136 million years. Despite the approximate coincidence between this extinction and flood basalt volcanism, existing geochronologic dates have insufficient resolution to confirm eruptive rates required to induce major climate perturbations. Here we present new zircon U-Pb geochronologic constraints on the age and duration of flood basalt volcanism within the Central Atlantic Magmatic Province. This chronology demonstrates synchroneity between the earliest volcanism and extinction, tests and corroborates the existing astrochronologic time scale, and shows that the release of magma and associated atmospheric flux occurred in four pulses over ~600,000 years, indicating expansive volcanism even as the biologic recovery was under way.
Reevaluation of the Enigmatic Archosaur Dyoplax arenaceus from the Upper Triassic of Germany
Maisch, M. W., Matzke, A. T., and T. Rathgeber. 2013. Re-evaluation of the enigmatic archosaur Dyoplax arenaceus O. Fraas, 1867 from the Schilfsandstein (Stuttgart Formation, lower Carnian, Upper Triassic) of Stuttgart, Germany. Neues Jahrbuch für Geologie und Paläontologie - Abhandlungen 267(3): 353-362
DOI: http://dx.doi.org/10.1127/
Abstract - The holotype and only specimen of the small suchian archosaur Dyoplax arenaceus O. Fraas, 1867 from the Stuttgart-Formation (Schilfsandstein) of southwestern Germany is partially redescribed and re-evaluated. The type locality can be identified as Stuttgart, not Stuttgart-Feuerbach as erroneously suggested by previous authors. A re-description of the skull and the dorsal armour provides several new characters and a restoration of the skull is attempted for the first time. The phylogenetic placement of Dyoplax is discussed. Although it is agreed with previous authors that the taxon is not an aetosaur, its placement in Crocodylomorpha is questioned. Instead we demonstrate that Dyoplax has several important cranial and postcranial features in common with Erpetosuchus from the Late Triassic of Scotland and North America, and it is tentatively re-assigned to ?Erpetosuchidae.
DOI: http://dx.doi.org/10.1127/
Abstract - The holotype and only specimen of the small suchian archosaur Dyoplax arenaceus O. Fraas, 1867 from the Stuttgart-Formation (Schilfsandstein) of southwestern Germany is partially redescribed and re-evaluated. The type locality can be identified as Stuttgart, not Stuttgart-Feuerbach as erroneously suggested by previous authors. A re-description of the skull and the dorsal armour provides several new characters and a restoration of the skull is attempted for the first time. The phylogenetic placement of Dyoplax is discussed. Although it is agreed with previous authors that the taxon is not an aetosaur, its placement in Crocodylomorpha is questioned. Instead we demonstrate that Dyoplax has several important cranial and postcranial features in common with Erpetosuchus from the Late Triassic of Scotland and North America, and it is tentatively re-assigned to ?Erpetosuchidae.
Latest Permian Strata Preserved in the Western U.S.?
Saltzman, M. R., and A. R. C. Sedlacek. 2013. Chemostratigraphy indicates a relatively complete Late Permian to Early Triassic sequence in the western United States. Geology (early online) doi:10.1130/G33906.1
Abstract - Although the latest Permian mass extinction and associated δ13C excursion are well documented from the Tethys Ocean, carbonate rocks preserving these events in the eastern Panthalassic Ocean (western Pangea) are unknown. We present δ13Ccarb from the Gerster and Thaynes (Permian and Triassic) Formations in the western United States and document a negative excursion with no evidence for major breaks in continuity. To further constrain the age of the δ13Ccarb excursion in the absence of index fossils, we analyzed the same samples for 87Sr/86Sr. When examining our new carbon and Sr data in the context of biostratigraphy and sequence stratigraphy, we conclude that parts of the western United States may preserve carbonate successions that span the latest Permian extinction.
Abstract - Although the latest Permian mass extinction and associated δ13C excursion are well documented from the Tethys Ocean, carbonate rocks preserving these events in the eastern Panthalassic Ocean (western Pangea) are unknown. We present δ13Ccarb from the Gerster and Thaynes (Permian and Triassic) Formations in the western United States and document a negative excursion with no evidence for major breaks in continuity. To further constrain the age of the δ13Ccarb excursion in the absence of index fossils, we analyzed the same samples for 87Sr/86Sr. When examining our new carbon and Sr data in the context of biostratigraphy and sequence stratigraphy, we conclude that parts of the western United States may preserve carbonate successions that span the latest Permian extinction.
Triassic Marine Flooding Event Identified by a Vertebrate Bonebed
Reolid, M., Pérez-Valera, F., Benton, M. J., and J. Reolid. 2013. Marine flooding event in continental Triassic facies identified by a nothosaur and placodont bonebed (South Iberian Paleomargin). Facies (early online) DOI 10.1007/s10347-013-0360-6
Abstract - Sudden marine flooding within otherwise continental successions of the Triassic is unusual. The Tabular Cover of the SE paleomargin of the Iberian Massif is characterized by continental Triassic redbed facies composed of sandstones and siltstones, with gypsum-rich levels in the transition to Jurassic limestones. These Triassic deposits were developed in a fluvial-coastal system and they are 300 m thick in the Puente Génave-Villarrodrigo area, eastern Jaén Province, Spain. An unexpected sandstone-limestone unit in the lower part of this formation, recognized over more than 30 km, contains marine reptile bones in a storm bed or tsunami deposit. The lower part of this unit is characterized by a sandstone with sedimentary structures indicative of high-energy conditions as well as by fossil remains of marine reptiles. This bed ranges from 0 to 90 cm in thickness, and in some outcrops pinches out rapidly within a few meters. The upper part of the studied unit is a limestone with common trace fossils and abundant remains of marine reptiles, comprising isolated and fragmented pieces of sauropterygians (nothosaurs, pachypleurosaurs, and placodonts). Most abundant are vertebrae and ribs. In some outcrops, the top of this bed presents a dense accumulation of well-preserved small gastropods. The limestone is overlain by red siltstones and sandstones. The studied unit is interpreted as a marine deposit representing a high-energy event and records exceptional marine flooding in a distal fluvial environment, in fact the only open-marine deposit in the Villarrodrigo section. The sedimentary structures in the lower part of the unit are typical of high-energy deposits and indicate deposition in a single episode, probably related to a storm surge or a tsunami. The fragmentation, disarticulation, and dispersion of the vertebrate bones and the imbrication of bioclasts are consistent with a high-energy event that favored the concentration of bones according to size and density.
Abstract - Sudden marine flooding within otherwise continental successions of the Triassic is unusual. The Tabular Cover of the SE paleomargin of the Iberian Massif is characterized by continental Triassic redbed facies composed of sandstones and siltstones, with gypsum-rich levels in the transition to Jurassic limestones. These Triassic deposits were developed in a fluvial-coastal system and they are 300 m thick in the Puente Génave-Villarrodrigo area, eastern Jaén Province, Spain. An unexpected sandstone-limestone unit in the lower part of this formation, recognized over more than 30 km, contains marine reptile bones in a storm bed or tsunami deposit. The lower part of this unit is characterized by a sandstone with sedimentary structures indicative of high-energy conditions as well as by fossil remains of marine reptiles. This bed ranges from 0 to 90 cm in thickness, and in some outcrops pinches out rapidly within a few meters. The upper part of the studied unit is a limestone with common trace fossils and abundant remains of marine reptiles, comprising isolated and fragmented pieces of sauropterygians (nothosaurs, pachypleurosaurs, and placodonts). Most abundant are vertebrae and ribs. In some outcrops, the top of this bed presents a dense accumulation of well-preserved small gastropods. The limestone is overlain by red siltstones and sandstones. The studied unit is interpreted as a marine deposit representing a high-energy event and records exceptional marine flooding in a distal fluvial environment, in fact the only open-marine deposit in the Villarrodrigo section. The sedimentary structures in the lower part of the unit are typical of high-energy deposits and indicate deposition in a single episode, probably related to a storm surge or a tsunami. The fragmentation, disarticulation, and dispersion of the vertebrate bones and the imbrication of bioclasts are consistent with a high-energy event that favored the concentration of bones according to size and density.
Two New 'Rauisuchid' Papers
Weinbaum, J. C. 2013. Postcranial skeleton of Postosuchus kirkpatricki (Archosauria: Paracrocodylomorpha), from the upper Triassic of the United States. In Nesbitt, S. J., Desojo, J. B. and R. B. Irmis, (eds) Anatomy, Phylogeny and Palaeobiology of Early Archosaurs and their Kin. Geological Society, London, Special Publications, 379, http://dx.doi.org/10.1144/SP379.7
Abstract - Postosuchus kirkpatricki is a Late Triassic (Norian) ‘rauisuchid’ archosaur from North America. The initial description of the Postosuchus type material included elements from two poposaurids. This confusion has prevented adequate description of the material. Recent examination of the type material and other specimens of Postosuchus, and of related taxa, has helped clarify the osteology of Postosuchus. The type specimens represent c. 75% of the skeleton. Together with other referred material, Postosuchus remains one of the most completely known rauisuchids. The paratype skeleton, which is relatively complete, would have been c. 3.5–4 m in length, and the holotype would have been closer to 5–6 m.
Analysis of the postcranial skeleton of Postosuchus suggests that it may have been an obligate biped (based in part on limb proportions, which are similar to some theropod dinosaurs, the size of the manus (30% of the size of the pes) and the highly reduced nature of the digits and vertebral measurements). Possible postcranial autapomorphies of Postosuchus include a large, rugose triangular supra-acetabular buttress confluent with the dorsal margin of the iliac blade, and a symmetrical pes with digits two and three being roughly equal in length.
De Franca, M. A. G., Langer, M. C., and J. Ferigolo. 2013. The skull anatomy of Decuriasuchus quartacolonia (Pseudosuchia: Suchia: Loricata) from the middle Triassic of Brazil. In Nesbitt, S. J., Desojo, J. B. and R. B. Irmis, (eds) Anatomy, Phylogeny and Palaeobiology of Early Archosaurs and their Kin. Geological Society, London, Special Publications, 379, doi:10.1144/SP379.8
Abstract - Unlike most rauisuchians, which are known based on partially preserved specimens, fossils attributed to Decuriasuchus quartacolonia include a monotaxonomic assemblage composed of nine associated individuals (MCN-PV10.105a–i), three with almost complete skulls (MCN-PV10.105a,c,d), and a partial disarticulated skull (MCN-PV10.004) collected in the Middle Triassic (Ladinian, Dinodontosaurus Biozone) beds of the Santa Maria Formation, in south Brazil. Because of its completeness and possible phylogenetic position, as one of the most basal loricatans, D. quartacolonia is a key taxon for anatomic, evolutionary and biomechanical studies of rauisuchians. The comparative description of its osteology reveals that the skull and mandible of D.quartacolonia are very similar to those of cf. Prestosuchus chiniquensis and Saurosuchus galilei, sharing a drop-shaped subnarial fenestra, a subtriangular antorbital fenestra with an elongated and narrow anterior point, a ‘roman nosed’ nasal, and a posteroventrally oriented ridge on the lateral surface of the ventral ramus of the squamosal. Among the differences are the autapomorphies of D.quartacolonia: numerous maxillary teeth (17), lateral expansion of the nasal/lacrimal covering the antorbital fenestra dorsally, and squamosal and quadratojugal forming a subtriangular projection that invades the lower temporal fenestra.
Abstract - Postosuchus kirkpatricki is a Late Triassic (Norian) ‘rauisuchid’ archosaur from North America. The initial description of the Postosuchus type material included elements from two poposaurids. This confusion has prevented adequate description of the material. Recent examination of the type material and other specimens of Postosuchus, and of related taxa, has helped clarify the osteology of Postosuchus. The type specimens represent c. 75% of the skeleton. Together with other referred material, Postosuchus remains one of the most completely known rauisuchids. The paratype skeleton, which is relatively complete, would have been c. 3.5–4 m in length, and the holotype would have been closer to 5–6 m.
Analysis of the postcranial skeleton of Postosuchus suggests that it may have been an obligate biped (based in part on limb proportions, which are similar to some theropod dinosaurs, the size of the manus (30% of the size of the pes) and the highly reduced nature of the digits and vertebral measurements). Possible postcranial autapomorphies of Postosuchus include a large, rugose triangular supra-acetabular buttress confluent with the dorsal margin of the iliac blade, and a symmetrical pes with digits two and three being roughly equal in length.
De Franca, M. A. G., Langer, M. C., and J. Ferigolo. 2013. The skull anatomy of Decuriasuchus quartacolonia (Pseudosuchia: Suchia: Loricata) from the middle Triassic of Brazil. In Nesbitt, S. J., Desojo, J. B. and R. B. Irmis, (eds) Anatomy, Phylogeny and Palaeobiology of Early Archosaurs and their Kin. Geological Society, London, Special Publications, 379, doi:10.1144/SP379.8
Abstract - Unlike most rauisuchians, which are known based on partially preserved specimens, fossils attributed to Decuriasuchus quartacolonia include a monotaxonomic assemblage composed of nine associated individuals (MCN-PV10.105a–i), three with almost complete skulls (MCN-PV10.105a,c,d), and a partial disarticulated skull (MCN-PV10.004) collected in the Middle Triassic (Ladinian, Dinodontosaurus Biozone) beds of the Santa Maria Formation, in south Brazil. Because of its completeness and possible phylogenetic position, as one of the most basal loricatans, D. quartacolonia is a key taxon for anatomic, evolutionary and biomechanical studies of rauisuchians. The comparative description of its osteology reveals that the skull and mandible of D.quartacolonia are very similar to those of cf. Prestosuchus chiniquensis and Saurosuchus galilei, sharing a drop-shaped subnarial fenestra, a subtriangular antorbital fenestra with an elongated and narrow anterior point, a ‘roman nosed’ nasal, and a posteroventrally oriented ridge on the lateral surface of the ventral ramus of the squamosal. Among the differences are the autapomorphies of D.quartacolonia: numerous maxillary teeth (17), lateral expansion of the nasal/lacrimal covering the antorbital fenestra dorsally, and squamosal and quadratojugal forming a subtriangular projection that invades the lower temporal fenestra.
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