Triassic Tetrapods Research Articles

Geological structure and faunistic characteristics of the Mansurovo unique locality of early triassic tetrapods and ichnofossils, Orenburg Region

The geological features of the Mansurovo unique locality of the remains of tetrapods and ichnofossils, Orenburg Region (Gostevskaya Formation, Lower Olenekian Substage, Ustmylian Horizon) are considered. A layer-by-layer description cross-section of 16 ditchs and their correlation with the section construction along the line of ditchs are provided. The Mansurovo section, based on biostratigraphic (Wetlugasaurus malachovi grouping of the Wetlugasaurus Fauna) and lithologic-facies data, correlates with the middle part of the stratotype section of the Gostevskaya Formation (Buzuluk Depression of the East European Platform). The geological features of the locality indicate a heterogeneous structure of the identified four geological units of channel-floodplain genesis within the study area, which correspond to alternating sedimentation cycles. The genesis of deposits was clarified using structural-textural analysis and microlithological analysis of rocks in thin sections. The faunistic complex of tetrapods and macroflora, as well as unique complex of ichnofossils were also characterized. Based on the data of lithological-facial analysis, a sedimentation model of the genesis of the locality is presented, showing the uneven nature of sedimentation pattern due to the wandering of river branches and their periodic drying out in a hot and arid climate during the Early Olenekian. Taking into account paleontological data, taphonomy was analyzed, indicating the burial process in the river setting in strong current condition and the possible death of Temnospondyli in subaquatic conditions.

Geology and Paleontology of the Unique Mansurovo Locality of Early Triassic Tetrapods and Ichnofossils (Orenburg Region, Russia)

Geology and Paleontology of the Unique Mansurovo Locality of Early Triassic Tetrapods and Ichnofossils (Orenburg Region, Russia)

A new sphenodontian (Diapsida: Lepidosauria) from the Upper Triassic (Norian) of Germany and its implications for the mode of sphenodontian evolution

The Arnstadt Formation of Saxony-Anhalt, Germany has yielded some of Germany’s most substantial finds of Late Triassic tetrapods, including the sauropodomorph Plateosaurus and the stem-turtle Proganochelys quenstedti. Here, we describe an almost complete skull of a new sphenodontian taxon from this formation (Norian, 227–208 Ma), making it the oldest known articulated sphenodontian skull from Europe and one of the oldest in the world. The material is represented by the dermal skull roof and by the complete maxilla and temporal region, as well as parts of the palate, braincase, and lower jaw. A phylogenetic assessment recovers it as a basal sphenodontian closely related to Planocephalosaurus robinsonae and to Eusphenodontia, making it the earliest-diverging sphenodontian known with an articulated skull. Its cranial anatomy is generally similar to the well-known Diphydontosaurus avonis from the Rhaetian of England, showing that this successful phenotype was already established in the clade around 10 myr earlier than assumed. An analysis of evolutionary change rates recovers high rates of evolution in basal sphenodontians, with decreasing rates throughout the evolution of the group. However, contrary to previous studies, reversals in this trend were identified, indicating additional peaks of evolutionary change. These results improve our understanding of the early sphenodontian diversity in Europe, providing critical information on evolutionary trends throughout the history of the clade and sparking renewed interest in its evolution.

The dawn of an Era: New contributions on comparative and functional anatomy of Triassic tetrapods.

The Triassic period stands as a crucial moment for understanding tetrapod evolution, marking the emergence and early diversification of numerous lineages that persist in today's ecosystems. Birds, crocodiles, testudines, lizards, and mammals can all trace their origins to the Triassic, which is distinguished by several adaptive radiation events that fostered unparalleled diversity in body plans and lifestyles. Beyond this macroevolutionary significance, the Triassic period serves as fertile ground for scientific inquiry, especially in tetrapod studies. The aim of this Special Issue is to assemble a diverse array of new contributions focused on continental Triassic tetrapods globally, encouraging collaboration among researchers across generations, pooling their efforts to comprehend this pivotal moment in tetrapod evolutionary history. This issue encompasses almost 40 varied contributions, spanning topics from comparative and functional anatomy, including descriptions of novel taxa, comprehensive anatomical reviews, systematic investigations, phylogenetic analyses, paleoneurological studies, biomechanical assessments, and detailed examinations of histology and ontogeny. Collectively, this Special Issue offers an extensive exploration of Triassic tetrapods from anatomical, ecological, and evolutionary perspectives, unveiling fresh insights into this intriguing moment in vertebrate evolutionary history.

A new early-diverging probainognathian cynodont and a revision of the occurrence of cf. Aleodon from the Chañares Formation, northwestern Argentina: New clues on the faunistic composition of the latest Middle-?earliest Late Triassic Tarjadia Assemblage Zone.

The Chañares Formation (Ischigualasto-Villa Unión Basin) is worldwide known by its exquisitely preserved fossil record of latest Middle-to-early Late Triassic tetrapods, including erpetosuchids, "rauisuchians," proterochampsids, gracilisuchids, dinosauromorphs, pterosauromorphs, kannemeyeriiform dicynodonts, and traversodontid, chiniquodontid and probainognathid cynodonts, coming from the Tarjadia (bottom) and Massetognathus-Chanaresuchus (top) Assemblage Zones of its lower member. Regarding cynodonts, most of its profuse knowledge comes from the traditional layers discovered by Alfred Romer and his team in the 1960s that are now enclosed in the Massetognathus-Chanaresuchus Assemblage Zone (AZ). In this contribution we focus our study on the probainognathian cynodonts discovered in levels of the Tarjadia Assemblage Zone. We describe a new chiniquodontid cynodont with transversely broad postcanine teeth (Riojanodon nenoi gen. et sp. nov.) which is related to the genus Aleodon. In addition, the specimen CRILAR-Pv 567 previously referred to cf. Aleodon is here described, compared, and included in a phylogenetic analysis. It is considered as an indeterminate Aleodontinae nov., a clade here proposed to included chiniquodontids with transversely broad upper and lower postcanines, by having a cuspidated sectorial labial margin and a lingual platform that is twice broader than a lingual cingulum. Cromptodon mamiferoides, from the Cerro de Las Cabras Formation (Cuyo Basin), was also included in the phylogenetic analysis and recovered as an Aleodontinae. The new cynodont and the record of Aleodontinae indet. reinforce the faunal differentiation between the Tarjadia and Massetognathus-Chanaresuchus Assemblage Zones, in the lower member of the Chañares Formation, and inform on the diverse chiniquodontid clade with both sectorial and transversely broad postcanine teeth.

Triassic Tetrapods of Russia

Triassic Tetrapods of Russia

Mechanistic Thermal Modeling of Late Triassic Terrestrial Amniotes Predicts Biogeographic Distribution

The biogeography of terrestrial amniotes is controlled by historical contingency interacting with paleoclimate, morphology and physiological constraints to dispersal. Thermal tolerance is the intersection between organismal requirements and climate conditions which constrains modern organisms to specific locations and was likely a major control on ancient tetrapods. Here, we test the extent of controls exerted by thermal tolerance on the biogeography of 13 Late Triassic tetrapods using a mechanistic modeling program, Niche Mapper. This program accounts for heat and mass transfer into and out of organisms within microclimates. We model our 13 tetrapods in four different climates (cool and warm at low and high latitudes) using environmental conditions that are set using geochemical proxy-based general circulation models. Organismal conditions for the taxa are from proxy-based physiological values and phylogenetic bracketing. We find that thermal tolerances are a sufficient predictor for the latitudinal distribution of our 13 test taxa in the Late Triassic. Our modeled small mammaliamorph can persist at high latitudes with nocturnal activity and daytime burrowing but large pseudosuchians are excluded because they cannot seek nighttime shelter in burrows to retain elevated body temperatures. Our work demonstrates physiological modeling is useful for quantitative testing of the thermal exclusion hypothesis for tetrapods in deep time.

Diverse assemblage of Middle Triassic continental tetrapods from the Newark Supergroup of Nova Scotia (Canada)

ABSTRACT Triassic strata of the Economy Member of the Wolfville Formation (Newark Supergroup) exposed along the shorelines in Colchester County, Nova Scotia, have yielded an assemblage of continental tetrapods that is clearly different from other Triassic tetrapod communities in eastern North America, including the Late Triassic (Carnian) one from the overlying Evangeline Member of the Wolfville Formation. Although dissociated and fragmentary, the skeletal elements document the presence of a lonchorhynchine trematosaurid and at least two taxa of capitosauroid temnospondyls, procolophonid parareptiles, several taxa of archosauromorph reptiles, and a kannemeyeriiform dicynodont synapsid. Particularly noteworthy is the first definite record of the long-necked archosauromorph Tanystropheus from eastern North America. The strata of the Economy Member were deposited in a semiarid setting but the presence of various temnospondyls indicates the existence of perennial bodies of water. The age of this unit has long been regarded as Middle Triassic (Anisian to Ladinian) based on the tetrapod record, and the present study supports this assessment. The tetrapod assemblage most closely resembles those from the upper Moenkopi Formation of the American Southwest and the upper Middle to Upper Buntsandstein of Germany. The Economy Member is the oldest known Triassic tetrapod-bearing stratigraphic unit as well as the first occurrence of Middle Triassic continental tetrapods in eastern North America.

Description of the metoposauridAnaschisma brownifrom the New Oxford Formation of Pennsylvania

AbstractMetoposaurids are a widespread and ubiquitous constituent of Late Triassic non-marine paleoenvironments. In North America, this group is practically the only large-bodied temnospondyl clade, and is particularly well documented from the American southwest and south-central regions (Arizona, New Mexico, Texas). However, metoposaurids are poorly documented from eastern North America, with fragmentary, doubtfully diagnostic historical material such as “Dictyocephalus elegans” Leidy, 1856 and “Eupelor durus” Cope, 1866. The Zions View (early Norian?) locality in Pennsylvania preserves more-complete material, which previous workers noted as belonging to “Buettneria perfecta” Case, 1922 (=Anaschisma browniBranson, 1905). However, the material has never been described in a fashion that characterizes the anatomy or that justifies the taxonomic assignment, yet it would represent the most complete material in eastern North America and a substantial expansion of this taxon's geographic range. Here we redescribe the Zions View metoposaurid material in detail, differentiating it fromCalamops paludosusSinclair, 1917, the only other Late Triassic temnospondyl from the eastern seaboard, and demonstrating confident affinities withA.browni. Our study is the first to properly justify the taxonomic referral, underscoring the broader importance of proper documentation of voucher specimens, especially for potential geographic outliers.Anaschisma browniis thus the most widely dispersed metoposaurid. Its easternmost documentation underscores the importance of the undersampled and understudied metoposaurid record on the eastern seaboard for understanding the development of a metoposaurid zone of exclusivity in North America and demonstrates the need for further exploration to refine conceptualizations of Late Triassic tetrapod evolution.

Climatic drivers of latitudinal variation in Late Triassic tetrapod diversity

AbstractThe latitudinal biodiversity gradient (LBG), the increase in biodiversity from the poles to the equator, is one of the most widely recognized global macroecological patterns, yet its deep time evolution and drivers remain uncertain. The Late Triassic (237–201 Ma), a critical interval for the early evolution and radiation of modern tetrapod groups (e.g. crocodylomorphs, dinosaurs, mammaliamorphs), offers a unique opportunity to explore the palaeolatitudinal patterns of tetrapod diversity since it is extensively sampled spatially when compared with other pre‐Cenozoic intervals, particularly at lower palaeolatitudes. Here, we explore palaeolatitudinal patterns of Late Triassic tetrapod diversity by applying sampling standardization to comprehensive occurrence data from the Paleobiology Database (PBDB). We then use palaeoclimatic model simulations to explore the palaeoclimatic ranges occupied by major tetrapod groups, allowing insight into the influence of palaeoclimate on the palaeolatitudinal distribution of these groups. Our results show that Late Triassic tetrapods generally do not conform to a modern‐type LBG; instead, sampling‐standardized species richness is highest at mid‐palaeolatitudes. In contrast, the richness of pseudosuchians (crocodylians and their relatives) is highest at the palaeoequator, a pattern that is retained throughout their subsequent evolutionary history. Pseudosuchians generally occupied a more restricted range of palaeoclimatic conditions than other tetrapod groups, a condition analogous to modern day reptilian ectotherms, while avemetatarsalians (the archosaur group containing dinosaurs and pterosaurs) exhibit comparatively wider ranges, which is more similar to modern endotherms, such as birds and mammals, suggesting important implications for the evolution of thermal physiology in dinosaurs.

Rare and Endemic Elements in Triassic Tetrapod Assemblages of Obshchii Syrt Highland (Eastern Europe)

The historical sequence of Early Triassic tetrapod communities in the Obshchii Syrt area includes eight consecutive faunal assemblages: this degree of detail in the identification of evolutionary stages is unique on a global scale. Temnospondyl amphibians are the dominant elements in these tetrapod assemblages, with three capitosauromorph groups (capitosaurids, benthosuchids, and trematosaurids) characterized by the widest distribution. Reptile remains are much less frequent. The paper provides a brief overview of the findings of rare and endemic tetrapod groups known from the Lower Triassic of Obshchii Syrt. These include amphibians (qantasids, lonchorhynchids, selenocarine capitosaurids, rhytidosteids, plagiosaurs, some forms of benthosuchids and trematosaurids, and chroniosuchians, the relict anthracosaurs) and reptiles (eosauropterygians, theriodonts, individual procolophonid, protorosaurian, and thecodontian genera). The peculiarity of the systematic composition of the Early Triassic tetrapod communities of Obshchii Syrt and Southern Cis-Urals with respect to that of the coeval fauna of terrestrial vertebrates of the more northern regions of Eastern Europe is emphasized, as is the legitimacy of considering these two areas as a specific region characterized by the distinctive character of their zoogeographical connections.

The Late Triassic Ischigualasto Formation at Cerro Las Lajas (La Rioja, Argentina): fossil tetrapods, high-resolution chronostratigraphy, and faunal correlations

Present knowledge of Late Triassic tetrapod evolution, including the rise of dinosaurs, relies heavily on the fossil-rich continental deposits of South America, their precise depositional histories and correlations. We report on an extended succession of the Ischigualasto Formation exposed in the Hoyada del Cerro Las Lajas (La Rioja, Argentina), where more than 100 tetrapod fossils were newly collected, augmented by historical finds such as the ornithosuchid Venaticosuchus rusconii and the putative ornithischian Pisanosaurus mertii. Detailed lithostratigraphy combined with high-precision U–Pb geochronology from three intercalated tuffs are used to construct a robust Bayesian age model for the formation, constraining its deposition between 230.2 ± 1.9 Ma and 221.4 ± 1.2 Ma, and its fossil-bearing interval to 229.20 + 0.11/− 0.15–226.85 + 1.45/− 2.01 Ma. The latter is divided into a lower Hyperodapedon and an upper Teyumbaita biozones, based on the ranges of the eponymous rhynchosaurs, allowing biostratigraphic correlations to elsewhere in the Ischigualasto-Villa Unión Basin, as well as to the Paraná Basin in Brazil. The temporally calibrated Ischigualasto biostratigraphy suggests the persistence of rhynchosaur-dominated faunas into the earliest Norian. Our ca. 229 Ma age assignment to Pi. mertii partially fills the ghost lineage between younger ornithischian records and the oldest known saurischians at ca. 233 Ma.

First Triassic tetrapod (Eusauropterygia) in the Triassic of the Subbetic domain of the Betic Cordillera (Southeastern Spain)

Sauropterygian vertebrate remains from the Ladinian (Middle Triassic) of the proximity of Calasparra (Murcia, Spain) are described here. They represent the first documented Triassic vertebrate remains found in the Province of Murcia, and the first in the Subbetic domain of the Betic Cordillera (Southeastern Spain). These new remains consist of incomplete vertebrae, some fragmented neural spine apophyses, fragments of transverse processes, a partial thoracic vertebrae mould and one isolated thoracic vertebral centrum, seemingly of a single specimen. Their features permit to refer them to the suborder Eusauropterygia. These fossils have been found in the middle part of the upper member of the Cehegin Formation. The biostratigraphical framework of the Cehegin Formation consists of a relatively abundant fossil content that allowed its attribution to the uppermost Fassanian (Lower Ladinian). The sedimentary features and the palaeontological content of the site are typical of an epicontinental platform.

Biostratigraphic significance of the tetrapod assem¬blages of the Timan- North Urals region and adjacent areas

New and specified data on the composition of the Triassic tetrapod assemblages of the Timan-North Urals region, the Mezen syneclise and the eastern part of the Moscow syneclise have been given. The succession of the Triassic tetrapod communities known in this area includes eight assemblages, seven of which correspond to the contemporary communities of the terrestial vertebrates known from other regions of the East European platform and the Cisurals. The first assemblage, known from the basal Triassic of the Mezen and Moscow syneclises, is Early Induan in age. The second, third and fourth assemblages are dated by Early Olenekian age and typical for the middle part of the Early Tri-assic section of the Timan-North Urals region, the Mezen and Moscow syneclises. The Late Olenekian fifth and sixth assemblages characterize the upper part of the Lower Triassic of the Northern Cisurals, the Moscow and Mezen syneclises. The seventh assemblage characterizes the base of the Middle Triassic (Lower Anisian) of the Northern Cisurals and has no analogues in other regions of the platform and of the Cisurals. The eighth assemblage is known from the upper part of the Middle Triassic of the Northern Cisurals and is Late Ladinian in age.

About the monograph «Early Trlassic amphibians of Eastern Europe: evolution of dominant groups and peculiarities of communities change»

The monograph is the first generalizing study on the fauna of the early Triassic amphibians of Eastern Europe, which reviews data on its taxonomic diversity, origin and ways of diversification of dominant groups, as well as their stratigraphic and geographical distribution. Original new ideas about the phylogenetic connections of separate taxa have been stated, stages of formation and the initial radiation of the dominant groups have been revealed and characterized. On this basis, the history of the development of Eastern European early Triassic tetrapods, known as the most fully documented in the world for that time, has been detailed. Significant changes have been made to the biostratigraphic scheme of the continental Lower Triassic of Eastern Europe for tetrapods, which made it possible to clarify or justify for the first time the age of a number of stratons, previously identified there.

Accounting for differences in species frequency distributions when calculating beta diversity in the fossil record

Abstract Beta diversity is a measure of the taxonomic differentiation between habitats/localities within an assemblage, and is normally calculated as a set of pairwise taxonomic “distances” between the localities. Due to incomplete sampling, beta diversity estimates for fossil assemblages will always be higher than the true value. However, the difference between the observed and true distances will vary greatly depending on differences in the shape of the relative abundance distribution. Using simulations, it is shown that incomplete sampling of a homogenous fauna with more even relative abundances of taxa produces higher beta diversity than one with very few extremely common taxa. A new procedure is proposed for calculating beta diversity in the fossil record, whereby the observed distances are compared to the distance obtained by randomly resampling a homogenous fauna with the same abundance distribution. This procedure is named Relative Abundance Corrected beta diversity. Simulations indicate that this method outperforms raw beta diversity estimates, providing beta diversity estimates closer to the true values even when the assumptions of the method are violated. This method is applied to an empirical dataset: Permian–Triassic tetrapods from the Karoo Supergroup of South Africa. Increased provincialism is found across the Permian–Triassic boundary in contrast to uncorrected beta diversity patterns.

First report of dinosaurian claws from the Late Triassic of India

The Late Triassic Tiki Formation has yielded five isolated nearly complete claws or ungual phalanges from a fossil locality, which are described in detail and compared with other Late Triassic tetrapods. Of these, four ungual phalanges are slender, asymmetric, ventrally recurved, transversely compressed, and contain deep collateral grooves on either side, a low median keel on the proximal articular surface and a prominent proximoventral flexor tubercle showing their high similarity to the theropod dinosaurs. The remaining claw is unlike that of any theropods in terms of high robusticity and near symmetry. However, as in dinosaurs it is ventrally recurved and contains deep lateral grooves, a small flexor tubercle, lateromedially extended proximal articular surface with a distinct median keel and is considered as belonging to an indeterminate dinosaur. Although it is not possible to ascertain whether the unguals belong to a single taxon or multiple taxa, this new find points towards the presence of small dinosaurs in the Late Triassic Tiki fauna.

Deep faunistic turnovers preceded the rise of dinosaurs in southwestern Pangaea.

The Triassic period documents the origin and diversification of modern amniote lineages and the Late Triassic fossil record of South America has been crucial to shed light on these early evolutionary histories. However, the faunistic changes that led to the establishment of Late Triassic ecosystems are largely ignored because of the global scarcity of fossils from assemblages a few million years older. Here we contribute to fill this gap with the description of a new tetrapod assemblage from the lowermost levels of the Chañares Formation (uppermost Middle-lower Late Triassic epochs) of Argentina, which is older than the other vertebrate assemblages of the same basin. The new assemblage is composed of therapsids, rhynchosaurids and archosaurs, and clearly differs from that of the immediately overlying and well-known historical Chañares vertebrate assemblage. The new tetrapod association is part of a phase of relatively rapidly changing vertebrate assemblage compositions, in a time span shorter than 6 million years, before the diversification of dinosaurs and other common Late Triassic tetrapods in southwestern Pangaea.

A new horned and long-necked herbivorous stem-archosaur from the Middle Triassic of India

The early evolution of archosauromorphs (bird- and crocodile-line archosaurs and stem-archosaurs) represents an important case of adaptive radiation that occurred in the aftermath of the Permo-Triassic mass extinction. Here we enrich the early archosauromorph record with the description of a moderately large (3–4 m in total length), herbivorous new allokotosaurian, Shringasaurus indicus, from the early Middle Triassic of India. The most striking feature of Shringasaurus indicus is the presence of a pair of large supraorbital horns that resemble those of some ceratopsid dinosaurs. The presence of horns in the new species is dimorphic and, as occurs in horned extant bovid mammals, these structures were probably sexually selected and used as weapons in intraspecific combats. The relatively large size and unusual anatomy of Shringasaurus indicus broadens the morphological diversity of Early–Middle Triassic tetrapods and complements the understanding of the evolutionary mechanisms involved in the early archosauromorph diversification.

A new extreme longirostrine temnospondyl from the Triassic of Madagascar: phylogenetic and palaeobiogeographical implications for trematosaurids

Trematosaurids form a very large and remarkable clade of Triassic tetrapods (Temnospondyli: Stereospondyli) with a worldwide geographical distribution. Compared with specimens from Europe, Australia or North America, they remain relatively scarce in African rocks, where they are mainly known in the Early Triassic of Madagascar and South Africa. Longirostrine trematosaurids were only known from Madagascar, represented by the genus Wantzosaurus. However, we describe herein a new species of the longirostrine trematosaurid Aphaneramma, Aphaneramma gavialimimus sp. nov., from the Olenekian (Lower Triassic) of Madagascar. This genus was previously known from the Early Triassic of Europe and Asia. Based on a new nearly complete skull, the new species is characterized by a premaxilla-nasal suture anteriorly directed, not contacting the nostrils; choanae completely included within the palatines; the ventral opening of the orbits in the anterior part of the interpterygoid vacuities; a very elongated nasal covering more than 50% of the prenarial length; and an anteriorly widened cultriform process. Aphaneramma gavialimimus sp. nov., with a skull length of about 40 cm, may be one of the largest known trematosaurids. Its inclusion in a new phylogenetic analysis confirms its close affinities with the North American genus Cosgriffius, and clarifies the relationships of trematosaurids in general and lonchorhynchines in particular. The new species also increases the palaeobiodiversity of marine trematosaurs in Gondwana and allows discussing their apparently rapid cosmopolitanism just after the great Permian–Triassic mass extinction.http://zoobank.org/urn:lsid:zoobank.org:pub:6992EB6B-5708-4226-860D-47982CFB7F22