Field of Science

Paleohistological Estimation of Bone Growth Rate in Extinct Archosaurs


Cubo, J., LeRoy, N., Martinez-Maza, C., and L. Montes. 2012. Paleohistological estimation of bone growth rate in extinct archosaurs. Paleobiology 38:335-339. doi: http://dx.doi.org/10.1666/08093.1

Abstract - The clade Archosauria contains two very different sister groups in terms of diversity (number of species) and disparity (phenotypic variation): Crurotarsi (taxa more closely related to crocodiles than to birds) and Ornithodira (pterosaurs and dinosaurs including birds). The extant species of Crurotarsi may constitute a biased sample of past biodiversity regarding growth patterns and metabolic rates. Bone histological characters can be conserved over hundreds of millions of years in the fossil record and potentially contain information about individual age at death, age at sexual maturity, bone growth rates, and basal metabolic rates of extinct vertebrates. Using a sample of extant amniotes, we have constructed a paleobiological model to estimate bone growth rate from bone histological traits. Cross-validation tests show that this model is reliable. We then used it to estimate bone growth rates in a sample of extinct archosaurs including Crurotarsi and Ornithodira. After testing for phylogenetic signal, optimization of femoral growth rates through squared change parsimony onto a time-calibrated tree of amniotes shows two divergent evolutionary trends: whereas bone growth rates increase from the last common ancestor of Ornithodira to extant birds, they decrease from the last common ancestor of Crurotarsi to extant crocodiles. However, we conclude, on the basis of recent evidence for unidirectional airflow in the lungs of alligators, that crocodiles may have retained the capacity of growing at high rates.

Vegetation History and Climate Change Across the Tr/J Boundary


Bonis, N. R., and W. M. Kürschner. 2012. Vegetation history, diversity patterns, and climate change across the Triassic/Jurassic boundary. Paleobiology 38:240-264. doi: http://dx.doi.org/10.1666/09071.1

Abstract - High-resolution palynological data sets from shallow marine Triassic-Jurassic (Tr/J) boundary beds of two principal sections in Europe (Hochalplgraben in Austria and St. Audrie's Bay in the United Kingdom) were analyzed to reconstruct changes in vegetation, biodiversity, and climate. In Hochalplgraben, a hardwood gymnosperm forest with conifers and seed ferns is replaced by vegetation with dominant ferns, club mosses and liverworts, which concurs with an increased diversification of spore types during the latest Rhaetian. Multivariate statistical analysis reveals a trend to warmer and wetter conditions across the Tr/J boundary in Hochalplgraben. The vegetation changes in St. Audrie's Bay are markedly different. Here, a mixed gymnosperm forest is replaced by monotonous vegetation consisting mainly of Cheirolepidiaceae (80–100%). This change is caused by a transition to a warmer and more arid climate. The observed diversity decrease in St. Audrie's Bay affirms this interpretation. Although both sections show major vegetation changes, neither of them demonstrates a distinctive floral mass extinction. A compilation of Tr/J boundary sections across the world demonstrates the presence of Cheirolepidiaceae-dominated forests in the Pangaean interior and increases in abundance of spore-producing plants adjacent to the Tethys Ocean. We propose that the non-uniform vegetation changes reflected in the Tr/J palynological records are the result of environmental changes caused by Central Atlantic Magmatic Province volcanism. The increase in greenhouse gases caused a warmer climate and an enhanced thermal contrast between the continent and the seas. Consequently, the monsoon system got stronger and induced a drier continental interior and more intensive rainfall near the margins of the Tethys Ocean.

Postcranial Skeletal Pneumaticity in Triassic Archosaurs


Butler, R. J., Barrett, P. M., and D. J. Gower. 2012. Reassessment of the evidence for postcranial skeletal pneumaticity in Triassic archosaurs, and the early evolution of the avian respiratory system. PLoS ONE 7(3): e34094. doi:10.1371/journal.pone.0034094


Abstract - Uniquely among extant vertebrates, birds possess complex respiratory systems characterised by the combination of small, rigid lungs, extensive pulmonary air sacs that possess diverticula that invade (pneumatise) the postcranial skeleton, unidirectional ventilation of the lungs, and efficient crosscurrent gas exchange. Crocodilians, the only other living archosaurs, also possess unidirectional lung ventilation, but lack true air sacs and postcranial skeletal pneumaticity (PSP). PSP can be used to infer the presence of avian-like pulmonary air sacs in several extinct archosaur clades (non-avian theropod dinosaurs, sauropod dinosaurs and pterosaurs). However, the evolution of respiratory systems in other archosaurs, especially in the lineage leading to crocodilians, is poorly documented. Here, we use mCT-scanning to investigate the vertebral anatomy of Triassic archosaur taxa, from both the avian and crocodilian lineages as well as non-archosaurian diapsid outgroups. Our results confirm previous suggestions that unambiguous evidence of PSP (presence of internal pneumatic cavities linked to the exterior by foramina) is found only in bird-line (ornithodiran) archosaurs. We propose that pulmonary air sacs were present in the common ancestor of Ornithodira and may have been subsequently lost or reduced in some members of the clade (notably in ornithischian dinosaurs). The development of these avian-like respiratory features might have been linked to inferred increases in activity levels among ornithodirans. By contrast, no crocodile-line archosaur (pseudosuchian) exhibits evidence for unambiguous PSP, but many of these taxa possess the complex array of vertebral laminae and fossae that always accompany the presence of air sacs in ornithodirans. These laminae and fossae are likely homologous with those in ornithodirans, which suggests the need for further investigation of the hypothesis that a reduced, or non-invasive, system of pulmonary air sacs may be have been present in these taxa (and secondarily lost in extant crocodilians) and was potentially primitive for Archosauria as a whole.

Taphonomy of an Upper Triassic Rhynchosaur Bonebed From India


Mukherje, D. and  & S. Ray. 2012. Taphonomy of an Upper Triassic vertebrate bonebed: A new rhynchosaur (Reptilia; Archosauromorpha) accumulation from India. Palaeogeography, Palaeoclimatology, Palaeoecology (advance online publication) http://dx.doi.org/10.1016/j.palaeo.2012.03.010


Abstract - The Upper Triassic Tiki Formation of India is a rich storehouse of varied vertebrate fossil assemblages. So far, there is no information on taphonomic signatures of the Tiki vertebrate assemblages in comparison to that of other fossiliferous horizons of India. We report a new, low diversity, mono-dominant, multitaxic vertebrate accumulation where rhynchosaurs constitute the dominant component. The formation of the rhynchosaur bonebed is attributed to biological aggregation with a hydraulic overprint resulting in a mixed-origin concentration. Other taxa include rauisuchid, phytosaur, small indeterminate archosaur and cynodonts. Taphonomic study based on 617 skeletal specimens of rhynchosaurs collected from nine sites within an area of about 250x217 sq m shows that most of the specimens are disarticulated and disassociated but in close spatial proximity to one another; some are associated specimens and few are articulated. About 13 to 20 individuals of rhynchosaur at different ontogenetic stages are estimated from the specimens collected, suggesting gregarious behaviour, possibly herding. These specimens show varying degree of weathering, breakage, encrustation, abrasion and deformation. The bonebed is preserved within the Tiki red mudstone unit and is found in association with paleosol profiles, suggesting prolonged subaerial exposure. Spatial distribution and relative bone frequencies show differential susceptibility of the skeletal specimens to fluvial transport. 55.4% of the collected skeletal specimens belonged to Voorhies Group I, whereas 12.4% and 24% constituted Voorhies Group II and III respectively, and 8.2% of the collected specimens belonged to the intermediate group I and II. It appears that the animals concentrated in the vicinity of the water sources during prolonged period of aridity and died possibly during high seasonal rainfall that resulted in a major flood event. Subsequently, the soft tissues decomposed, and the skeletons suffered prolonged subaerial exposure when the water receded leading to disarticulation and fragmentation followed by minor dispersion by low velocity water currents. This resulted in segregation of skeletal specimens, which were gradually covered by mud deposited during later flooding events. Based on the known flora and fauna, the Tiki Upper Triassic ecosystem is reconstructed for the first time. In the aquatic ecosystem, the metoposaurid labyrinthodonts occupied the top of the food pyramid together with the semi-aquatic parasuchids, which occupied an ecological niche similar to that of the present day crocodilians. The abundance of herbivorous rhynchosaurs at the base with few large and carnivorous rauisuchids and parasuchids at the top suggest a trophic structure similar to that of a modern day terrestrial ecosystem.

Revised Phylogeny of Basal Turtles


Anquetin, J. 2012. Reassessment of the phylogenetic interrelationships of basal turtles (Testudinata). Journal of Systematic Palaeontology 10:3-45. doi: http://dx.doi.org/10.1080/14772019.2011.558928


Abstract - Recent discoveries from the Late Triassic and Middle Jurassic have significantly improved the fossil record of early turtles. These new forms offer a unique opportunity to test the interrelationships of basal turtles. Nineteen fossil species are added to the taxon sample of the most comprehensive morphological phylogenetic analysis of the turtle clade. Among these additional species are recently discovered forms (e.g. Odontochelys semitestacea, Eileanchelys waldmani, Condorchelys antiqua), taxa generally omitted from previous analyses (e.g. chengyuchelyids, Sichuanchelys chowi) and species included in a phylogenetic analysis for the first time (Naomichelys speciosa and Siamochelys peninsularis). The coding of several characters is reassessed in the light of recent observations, but also in order to reduce unwarranted assumptions on character and character state homologies. Additional characters from previous analyses, as well as five new ones, are also included, resulting in a data matrix of 178 characters scored for 86 turtle species and seven fossil outgroups. The dataset resolves the relationships of most newly included taxa, with the exception of S. chowi and ‘Chengyuchelysdashanpuensis. The phylogenetic placement of Heckerochelys romani, Condorchelys antiqua and Eileanchelys waldmani as stem turtles more derived than Kayentachelys aprix but more basal than Meiolania platyceps and Mongolochelys efremovi is corroborated. The relationships of chengyuchelyids remain unclear and they are unstable with respect to stem turtles. In contrast to previous analyses, Arundelemys dardeni is placed within pleurosternids and Siamochelys peninsularis falls within xinjiangchelyids. Perhaps the most salient conclusion of the present study is the placement of Naomichelys speciosa as a basal member of a clade uniting meiolaniids, Mongolochelys efremovi and Otwayemys cunicularius. This clade of rather large stem turtles had a worldwide spread during the Mesozoic at least, and persisted until the Pleistocene with meiolaniids.

Further Evidence of Burrowing in Procolophonid Parareptiles


MacDougall, M. J., Modesto, S. P., and J. Botha-Brink. 2012. The postcranial skeleton of the Early Triassic parareptile Sauropareion anoplus, with a discussion of possible life history. Acta Palaeontologica Polonica in press. Available online 27 Feb 2012 doi: http://dx.doi.org/10.4202/app.2011.0099.


Abstract - The skeletal anatomy of the Early Triassic (Induan) procolophonid reptile Sauropareion anoplus is described on the basis of three partial skeletons from Vangfontein, Middelburg District, South Africa. Together these three specimens preserve the large majority of the pectoral and pelvic girdles, articulated forelimbs and hindlimbs, and all but the caudal portion of the vertebral column, elements hitherto undescribed. Our phylogenetic analysis of the Procolophonoidea is consonant with previous work, positing S. anoplus as the sister taxon to a clade composed of all other procolophonids exclusive of Coletta seca. Previous studies have suggested that procolophonids were burrowers, and this seems to have been the case for S. anoplus, based on comparisons with characteristic skeletal anatomy of living digging animals, such as the presence of a spade-shaped skull, robust phalanges, and large unguals.

Earliest Evidence of Ovoviviparity in Coelocanths

Wen, W., Zhang, Q.-Y., Hu, S.-X., Benton, M. J., Zhou, C.-Y., Tao, X., Yuan, H.-J., and Z.-Q., Chen. 2012. Coelacanths from the Middle Triassic Luoping Biota, Yunnan, South China, with the earliest evidence of ovoviviparity. Acta Palaeontologica Polonica in press. Available online 08 Mar 2012 doi: http://dx.doi.org/10.4202/app.2011.0066



Abstract - The fossil record of coelacanths is patchy, with very few taxa known from the Triassic of Asia. We report here two new genera and species of coelacanths from the Luoping Biota, a recently found site of exceptional fossil preservation from Yunnan, South China. The first new taxon, Luopingcoelacanthus eurylacrimalis, is based on four specimens, which together show most aspects of the anatomy. One specimen shows two small coelacanths inside the ventral portion of the abdominal cavity, and these are interpreted as intrauterine embryos, close to birth size, based on comparisons with previously reported embryos of the fossil coelacanths Rhabdoderma and Undina, and the extant genus Latimeria. Our new find extends the evidence for ovoviviparity in coelacanths back from the Late Jurassic to the Middle Triassic. The second new taxon, Yunnancoelacanthus acrotuberculatus, is based on one specimen, and differs from Luopingcoelacanthus in the dentary, lachrymojugal, number of rays of the first dorsal fin, and especially in the ornament on dermal bones and scales. A cladistic analysis shows that the new taxa are closest relatives to the derived clade Latimerioidei. The relatively high diversity of coelacanths in the Early Triassic, and adaptations of living Latimeria to low-oxygen conditions, suggests that the group may have included ‘disaster taxa’ that benefited from anoxic and dysoxic ocean conditions in the aftermath of the end-Permian mass extinction.

Early Evolution of Postcranial Skeletal Pneumaticity in Sauropodomorph Dinosaurs


I don't think I've posted this paper previously, but it has been in press for a year...

Yates, A. M., Wedel, M. J., and M. F. Bonnan. 2012. The early evolution of postcranial skeletal pneumaticity in sauropodomorph dinosaurs. Acta Palaeontologica Polonica 57:85-100.  
doi: http://dx.doi.org/10.4202/app.2010.0075

Abstract - Postcranial skeletal pneumaticity (PSP) is present in a range of basal sauropodomorphs spanning the basal sauropodomorph—sauropod transition. We describe the PSP of five taxa, Plateosaurus engelhardti, Eucnemesaurus fortis, Aardonyx celestae, Antetonitrus ingenipes, and an unnamed basal sauropod from Spion Kop, South Africa (hereafter referred to as the Spion Kop sauropod). The PSP of Plateosaurus is apparently sporadic in its occurrence and has only been observed in very few specimens, in which it is of very limited extent, affecting only the posterior cervical vertebrae and possibly the mid dorsals in one specimen. The PSP of Eucnemesaurus, Aardonyx, Antetonitrus, and the Spion Kop sauropod consists of subfossae (fossa within-fossa structures) that excavate the vertices of the posterior infradiapophyseal fossae of the posterior dorsal vertebrae. These subfossae range from simple shallow depressions (Eucnemesaurus) to deep, steepsided, internally subdivided and asymmetrically developed chambers (Antetonitrus). The middle and anterior dorsal vertebrae of these taxa lack PSP, demonstrating that abdominal air sacs were the source of the invasive diverticula. The presence of pneumatic features within the infradiapophyseal fossae suggest that the homologous fossae of more basal saurischians and dinosauriforms were receptacles that housed pneumatic diverticula. We suggest that it is probable that rigid non-compliant lungs ventilated by compliant posterior air sacs evolved prior to the origination of Dinosauria.

Panchetocynodon damodarensis, a New Cynodont from the Lower Triassic of India



Das, D. P., and A. Gupta. 2012. New cynodont record from the lower Triassic Panchet Formation, Damodar valley. Earth and Environmental Science Journal of the Geological Society of India Volume 79, Number 2, 175-180 DOI: 10.1007/s12594-012-0022-2


Abstract - This paper reports the find of a new non-mammalian cynodont from the Lower Triassic Panchet Formation of the Damodar valley, West Bengal, India. The fossil, recovered from a clay pellet rich calcareous sandstone bed, is a part of left lower jaw having five post canines that are damaged to various extents. A combination of mammal-like advanced characters such as much enlarged dentary, reduced post dentary bones, high coronoid process, large masseteric fossa, each post canine with a large central cusp flanked by a distal and a mesial accessory cusps with two additional lingually positioned cingular cusps, incipient root division and clearly demarcated crown-root juncture prompted to erect a new taxon Panchetocynodon damodarensis gen. et sp. nov.

Hind limb osteology of Gracilisuchus stipanicicorum


Lecuona, A., and J. B. Desojo 2011. Hind limb osteology of Gracilisuchus
stipanicicorum (Archosauria: Pseudosuchia). Earth and Environmental Science Transactions of the Royal Society of Edinburgh, 102, 105–128.


Abstract - Gracilisuchus stipanicicorum Romer, 1972, from the Middle-Late Triassic of the Ischigualasto–Villa Unio´n Basin of Argentina, is an extinct pseudosuchian archosaur on the stem to Crocodylomorpha. The pelvic girdle and hind limb anatomy of a referred specimen of Gracilisuchus stipanicicorum is described and compared with that from a broad range of archosauriform taxa, including basal members such as crurotarsans and basal ornithodirans. The description of this specimen reveals new information on the anatomy of the pelvic girdle and hind limb of Gracilisuchus, through a detailed examination of some anatomical regions barely or not previously described, as well as reinterpretations of previous features. The phylogenetic affinities of Gracilisuchus within the Archosauria remain to be tested, but Gracilisuchus shares two putative synapomorphies with some non-crocodyliform crocodylomorphs, providing tentative support for the monophyly of Sphenosuchia (e.g., Sereno & Wild 1992; Wu & Chatterjee 1993) and the close relationship of Gracilisuchus to that clade. These characteristics are: (i) the morphology and poor development of the femoral fourth trochanter, closely resembling the condition of Pseudhesperosuchus and Trialestes; and (ii) a poor anterior development of the femoral head, shared with Pseudhesperosuchus. On the other hand there are characters that reject the inclusion of Gracilisuchus within Crocodylomorpha (Nesbitt 2011), such as the absence of an imperforated acetabulum, and that rather suggests a sister-taxon position to Crocodylomorpha.

Reevaluation of Therapsid Fossils from Antarctica

Huttenlocker, A. K., and C. A. Sidor. 2012. Taxonomic Revision of Therocephalians (Therapsida: Theriodontia) from the Lower Triassic of Antarctica. American Museum Novitates Number 3738 :1-19.

Abstract - We reevaluate the taxonomic status of therocephalian fossils recovered from the lower Fremouw Formation (Lower Triassic) of the central Transantarctic Mountains, Antarctica. The material, which includes mostly fragmentary juvenile specimens, is reidentified using an apomorphy-based approach. We recognize the presence of three higher-level taxa: Eutherocephalia, Akidnognathidae, and Baurioidea. The only genus-level identification is for a partial lower jaw and pterygoid tentatively attributed to the baurioid, Ericiolacerta parva. An indeterminate theriodont partial skull is reassigned to the therocephalian family Akidnognathidae. The holotypes of Pedaeosaurus parvus and Rhigosaurus glacialis are represented by indeterminate juvenile baurioids and, in the absence of clear autapomorphies, are considered nomina dubia. The results of the taxonomic revision indicate that the therocephalian fauna of Antarctica lacks endemic genera and thus corresponds to that of the Triassic Lystrosaurus Assemblage Zone fauna of South Africa's Karoo Basin. More generally, we consider the southern Gondwanan basins of South Africa and Antarctica to sample a broadly distributed Lower Triassic tetrapod fauna, although the latter basin documents the first occurrence of several taxa (e.g., Kombuisia, Palacrodon). More precise (i.e., species-level) identifications are needed to better constrain the biogeographic signal for therocephalians, but the presence of juveniles strongly suggests that this group of therapsids, like dicynodonts, were year-round high-latitude inhabitants during Early Triassic times.

Possible New Plateosaurid Sauropodomorph From Brazil

Bittencourt, J.S., Leal, L.A., Langer, M.C. & Azevedo, S.A.K., iFirst article. An additional basal sauropodomorph specimen from the Upper Triassic Caturrita Formation, southern Brazil, with comments on the biogeography of plateosaurids. Alcheringa, 1–10.

Abstract - We describe an additional saurischian specimen from the Caturrita Formation (Norian) of the Parana Basin, southern Brazil. This material was collected in the 1950s and remained unstudied due to its fragmentary condition. Detailed comparisons with other saurischians worldwide reveal that some characters of the ilium, including the low ventral projection of the medial wall of the acetabulum and its concave ventral margin, together with the short triangular shape of the pre-acetabular process and its mound-like dorsocaudal edge, resemble those of sauropodomorphs such as Plateosaurus and Riojasaurus. This set of traits suggests that MN 1326-V has affinities with basal Sauropodomorpha, probably closer to plateosaurians than to Saturnalia-like taxa. Previous records of this clade in the Caturrita Formation include Unaysaurus, which has been related to Plateosaurus within Plateosauridae. Alternative schemes suggest that plateosaurids include Plateosaurus plus the Argentinean ‘prosauropods’ Coloradisaurus and Riojasaurus. Both hypotheses raise biogeographic questions, as a close relationship between faunas from South America and Europe excluding Africa and North America is not supported by geological and biostratigraphical evidence. Additionally, the absence of plateosaurids in other continents suggests that the geographical distribution of this taxon is inconsistent with the geological history of western Pangaea, and this demands further investigations of the phylogeny of sauropodomorphs or improved sampling.

Arachana nigra, a New Temnospondyl from the Permo-Triassic of Uruguay


Piñeiro, G., Ramos, A., and C. Marsicano. 2012. A rhinesuchid-like temnospondyl from the Permo-Triassic of Uruguay. Compte Rendus Palevol 11:65-78. http://dx.doi.org/10.1016/j.crpv.2011.07.007
 
Abstract - A new temnospondyl species, Arachana nigra, from the Permo-Triassic Buena Vista Formation of Uruguay is described. The holotypic and only known specimen consists of an almost complete skull lacking most of the snout, the tabular horns and the posterolateral corners of the skull table. As with other specimens from the same unit, Arachana shows a transitional morphology. It shares several characters with rhinesuchids, such as the large size and the general shape of the skull, orbits positioned slightly posterior to the skull roof mid-length, a coarsely pitted dermal ornamentation lacking pustules, and a smoothly convex cheek contour. The palatal ramus of the pterygoid suturing with the vomer, and excluding the palatine and ectopterygoid from the margin of the interpterygoid vacuity, and the presence of a small basioccipital, visible in both occipital and ventral view, also resemble the conditions found in rhinesuchids and other basal temnospondyls. Other characters present in Arachana, however, are commonly found in lydekkerinids, but are absent in almost all rhinesuchids: supratemporal excluded from otic notch; supraorbital and infraorbital sensory sulci encroaching the lacrimal, although lacking a step-like lacrimal flexure; otic notch not deeply incised; post-temporal fenestra large and rounded; occipital condyles well-separated from each other; palatine tooth row behind the palatine tusk reduced; pterygoid corpus slightly ornamented; and presence of an interorbital depression. This combination of primitive and derived characters is consistently present in most components of the Buena Vista fauna, which could thus be transitional between typical Permian and Triassic tetrapod communities found elsewhere. The location of the PTB in the Uruguayan sequence is controversial, mainly due to the lack of clear faunal correlations with other well-known sequences, such as those of southern Africa and Russia. Moreover, the mosaic-like character combinations in most of the recorded tetrapods ally them to both Triassic and Paleozoic groups, and this has complicated even more the possibility of age assignment. Transitional faunas associated with the PTB, such as the Russian Uppermost Permian faunas, could be equivalent to the unique Colonia Orozco fauna. If true, this scenario will substantially change estimates about survivorship rates, suggesting a speciation rate increase in temnospondyls after the Permian-Triassic event. Based on taxonomic, phylogenetic, and geochronologic data, the Buena Vista fauna allows us to quantify faunal turnover across the PTB and in the aftermath of the end Permian extinction event.

"Romer's Gap" Is Filled

Taking a quick break from all of the current Triassic papers because this is pretty significant for the field of vertebrate paleontology.

Smithson, T. R.,Wood, S. P., Marshall, J. E. A., and J. A. Clack. 2012. Earliest Carboniferous tetrapod and arthropod faunas from Scotland populate Romer's Gap. PNAS [advance online] doi: 10.1073/pnas.1117332109

Abstract - Devonian tetrapods (limbed vertebrates), known from an increasingly large number of localities, have been shown to be mainly aquatic with many primitive features. In contrast, the post-Devonian record is marked by an Early Mississippian temporal gap ranging from the earliest Carboniferous (Tournaisian and early Viséan) to the mid-Viséan. By the mid-Viséan, tetrapods had become effectively terrestrial as attested by the presence of stem amniotes, developed an essentially modern aspect, and given rise to the crown group. Up to now, only two localities have yielded tetrapod specimens from the Tournaisian stage: one in Scotland with a single articulated skeleton
and one in Nova Scotia with isolated bones, many of uncertain identity. We announce a series of discoveries of Tournaisian-age localities in Scotland that have yielded a wealth of new tetrapod and arthropod fossils. These include both terrestrial and aquatic forms and new taxa. We conclude that the gap in the fossil record has been an artifact of collection failure.

Evidence of Avian-like Behavior in a Basal Saurischian Dinosaur

There has been a rash of Triassic vertebrate papers in the last two weeks.  Here is one that looks at the taphonomy of a specimen of the basal saurischian Guaibasaurus and suggests that it had a avian style of resting.

Agnolin, F., and Martinelli, A.G. 2012. Guaibasaurus candelariensis (Dinosauria, Saurischia) and the early origin of avian-like resting posture. Alcheringa (1–5) [advance online] DOI:10.1080/03115518.2012.634203

Abstract - A specimen of the basal saurischian Guaibasaurus candelariensis Bonaparte, Ferigolo and Ribeiro (UFRGS-PV-0725-T) from the Faxinal do Soturno locality, Rio Grande do Sul State, Brazil (Caturrita Formation; Late Triassic) lacks any sign of post-mortem transport and burial deformation, and exhibits features (flexed forelimbs, folded hindlimbs under the body and curved neck) that indicate a typical avian-like resting position. The presence in Guaibasaurus of an avian-like resting posture and related physiological implications would extend this unique trait, previously considered restricted to derived maniraptoran theropods, to the base of the Theropoda (or even
Saurischia) clade.

Another Example of the Phylogenetic Utility of Osteoderms in Triassic Vertebrates

Buchwitz, M., C. Foth, I. Kogan, and S. Voigt. 2012. On the use of osteoderm features in a phylogenetic approach on the internal relationships of the Chroniosuchia (Tetrapoda: Reptiliomorpha). Palaeontology [Early View]. DOI: 10.1111/j.1475-4983.2012.01137.x

Abstract:  Chroniosuchians are an enigmatic Permian to Triassic group of crocodile-like basal tetrapods. Their conspicuous dorsal osteoderm systems include most of the group’s yet documented postcranial morphological variability but have hardly been considered in cladistic approaches. Aiming at the clarification of the internal relationships of the Chroniosuchia, we have carried out a parsimony analysis including, among others, 23 morphological and osteohistological osteoderm characters and 12 chroniosuchian taxa. According to the most parsimonious trees, taxa usually referred to Chroniosuchidae form a paraphyletic succession with Madygenerpeton pustulatus and Chroniosaurus dongusensis as the basalmost chroniosuchians and Uralerpeton tverdochlebovae as the sister group of Bystrowianidae (hypothesis A). However, the concurrent hypothesis of a basal split into monophyletic subtaxa Chroniosuchidae and Bystrowianidae (hypothesis B) is only slightly less parsimonious and supported by an alternative analysis which includes embolomeres as the only reptiliomorph outgroup. Searching for the better hypothesis, we compare the respective order of branching to the order of first occurrences in the fossil record, demonstrating that hypothesis A provides a better stratigraphic fit than hypothesis B. Accordingly, the last common ancestor of the yet known chroniosuchians had a series of broad complexly interlocking ‘chroniosuchid’ osteoderms that served as a protection carapace apart from supporting the trunk during terrestrial locomotion. The later evolution of chroniosuchian carapaces was marked by a stepwise increase in flexibility and size reduction, which resulted in a loss of protective function and in a reduction in trunk support function. The flexibility increase is paralleled by the evolution of the Crocodylomorpha whose extant members do not possess as extensively interlocking osteoderm systems as some of their Mesozoic relatives.

In addition you can read about more new articles on Kyrgyzsaurus and Longisquama here.

Chanaresuchus ischigualastensis, a New Proterochampsid from the Late Triassic of Argentina and a Temporal Range Extension for the Genus Chanaresuchus

This is a short communication in the new issue of the Journal of Vertebrate Paleontology. As such there is no abstract available.

Trotteyn, M. J., Martinez, R. N., and O. A. Alcober. 2012. A new proterochampsid Chanaresuchus ischigualastensis (Diapsida, Archosauriformes) in the early Late Triassic Ischigualasto Formation, Argentina. Journal of Vertebrate Paleontology 32:485-489. DOI:10.1080/02724634.2012.645975

The specimen includes much of an articulated skeleton including a well preserved skull. This is the first occurrence of Chanaresuchus outside of the Chanares Formation and marks an extension of the taxon into the Late Triassic. As the authors state, this is interesting because it demonstrates only a species level turnover for the clade between the late Middle and early Late Triassic faunas in the Ischiguasto Basin. Several therapsids also show the same pattern. This also marks the presence of two different proterochampsids in the Ischigualasto Formation.

From the discussion: "PVSJ 567 is assignable to Chanaresuchus on the basis of diagnostic characters shared with Chanaresuchus bonapartei (e.g., skull ornamented by longitudinal crests and depressions on the dorsal surfaces of the premaxillae, maxillae, and nasals; lateral fossa in the centra of presacral vertebrae; low deltopectoral crest on the humerus; absence of phalanges on pedal digit V). PVSJ 567 exhibits several differences from Chanaresuchus bonapartei and can be assigned to a new species, C. ischigualastensis (e.g., basal tubera wide with rostrolateral contour transversely oriented; paroccipital processes distally expanded; articular surface of caudal prezygapophyses elliptical and notably anteriorly developed; astragalus lacking perforations in the posterior sulcus; osteoderms with longitudinal dorsal sulcus).