Field of Science

First record of Colognathus (?Amniota) from the Middle Triassic of Europe

This is a short note redescribing material from the Middle Triassic of Germany that is referable to the enigmatic vertebrate taxon Colognathus, which has been considered everything from a 'fish' to and archosauromorph reptile. Unfortunately the new material does not clarify the systematic position of Colognathus, but does represent a temporal and geographic extension.

Sues, H. -D.,  and R. R. Schoch. 2013. First record of Colognathus (?Amniota) from the Middle Triassic of Europe, Journal of Vertebrate Paleontology, 33:4, 998-1002. http://dx.doi.org/10.1080/02724634.2013.732977

"Francosuchus" trauthi is Not a Phytosaur - Implications for Late Triassic Global Vertebrate Biostratigraphy

This eliminates the marine tie for the Otischalkian Land Vertebrate Faunachron, although the identification of this specimen as 'Paleorhinus' was already pretty weak as argued by Irmis et al. (2010).

Butler, R. J., 2013. ‘Francosuchus’ trauthi is not Paleorhinus: implications for Late Triassic
vertebrate biostratigraphy, Journal of Vertebrate Paleontology, 33:858-864. 

Abstract - A rostrum fragment from the marginal marine upper Lunz Formation of Austria (early Late Triassic: late Carnian) was previously identified as a new species of phytosaurian archosauriform, ‘Francosuchus’ trauthi. ‘Francosuchus’ trauthi was subsequently synonymized with the non-phytosaurid phytosaur Paleorhinus, and this synonymy was used as evidence to correlate the ‘Paleorhinus biochron’ and the Otischalkian land-vertebrate faunachron to the marine timescale. Here, I provide a redescription of ‘Francosuchus’ trauthi and document anatomical features that differ substantially from all known species of non-phytosaurid phytosaur. There is no evidence to support synonymy of ‘Francosuchus’ trauthi with Paleorhinus, and no unambiguous features to support a phytosaurian identification. However, ‘Francosuchus’ trauthi possesses a unique combination of characters that distinguish it from all other Triassic tetrapods, and necessitates referral of the species to a new genus, Dolerosaurus, gen. nov. Rejection of the proposed synonymy between ‘Francosuchus’ trauthi and Paleorhinus means that the ‘Paleorhinus biochron’ cannot be tied to the marine late Carnian as previously suggested, and provides further evidence of the problems inherent in attempting to correlate the terrestrial Triassic to the marine timescale.

Donald Baird and His Fieldwork in the Triassic-Jurassic of Nova Scotia

Sues, H.-D., Hook, R. W., and P. E. Olsen. 2013. Donald Baird and his discoveries of Carboniferous and early Mesozoic vertebrates in Nova Scotia. Atlantic Geology 49:90-103.

Abstract - Donald Baird (1926–2011), an influential and innovative vertebrate paleontologist with a scientific career spanning nearly 50 years, had an exceptional breadth of expertise in the study of late Paleozoic and Mesozoic vertebrates and their life traces. Beginning in 1956, Baird conducted fieldwork in the Carboniferous and Triassic-Jurassic of Nova Scotia, making a total of 21 trips in 30 years. His many scientific contributions include the discoveries of important assemblages of Carboniferous vertebrates as well as an unexpectedly diverse record of early Mesozoic tetrapods and their trackways in the province. Baird also encouraged and supported fieldwork by other vertebrate paleontologists as well as amateurs in Nova Scotia and elsewhere. His career-long commitment to the vertebrate paleontology of the province was instrumental in establishing it as an important source of fossils of Carboniferous and early Mesozoic continental vertebrates.

An Absolutely Beautiful (and Incredible) Fossil from the Early Triassic of South Africa

Fernandez, V., Abdala, F., Carlson, K.J., Cook, D.C., Rubidge, B.S., Yates, A., and P. Tafforeau. 2013. Synchrotron Reveals Early Triassic Odd Couple: Injured Amphibian and Aestivating Therapsid Share Burrow. PLoS ONE 8(6): e64978. doi:10.1371/journal.pone.0064978.

Abstract - Fossorialism is a beneficial adaptation for brooding, predator avoidance and protection from extreme climate. The abundance of fossilised burrow casts from the Early Triassic of southern Africa is viewed as a behavioural response by many tetrapods to the harsh conditions following the Permo-Triassic mass-extinction event. However, scarcity of vertebrate remains associated with these burrows leaves many ecological questions unanswered. Synchrotron scanning of a lithified burrow cast from the Early Triassic of the Karoo unveiled a unique mixed-species association: an injured temnospondyl amphibian (Broomistega) that sheltered in a burrow occupied by an aestivating therapsid (Thrinaxodon). The discovery of this rare rhinesuchid represents the first occurrence in the fossil record of a temnospondyl in a burrow. The amphibian skeleton shows signs of a crushing trauma with partially healed fractures on several consecutive ribs. The presence of a relatively large intruder in what is interpreted to be aThrinaxodon burrow implies that the therapsid tolerated the amphibian’s presence. Among possible explanations for such unlikely cohabitation, Thrinaxodon aestivation is most plausible, an interpretation supported by the numerous Thrinaxodon specimens fossilised in curled-up postures. Recent advances in synchrotron imaging have enabled visualization of the contents of burrow casts, thus providing a novel tool to elucidate not only anatomy but also ecology and biology of ancient tetrapods.

Aging, Maturation and Growth of Sauropodomorph Dinosaurs

Griebeler, E. M., Klein, N., and  P. M. Sander. 2013. Aging, Maturation and Growth of Sauropodomorph Dinosaurs as Deduced from Growth Curves Using Long Bone Histological Data: An Assessment of Methodological Constraints and Solutions. PLoS ONE 8(6): e67012. doi:10.1371/journal.pone.0067012

Abstract -
Information on aging, maturation, and growth is important for understanding life histories of organisms. In extinct dinosaurs, such information can be derived from the histological growth record preserved in the mid-shaft cortex of long bones. Here, we construct growth models to estimate ages at death, ages at sexual maturity, ages at which individuals were fully-grown, and maximum growth rates from the growth record preserved in long bones of six sauropod dinosaur individuals (one indeterminate mamenchisaurid, two Apatosaurus sp., two indeterminate diplodocids, and one Camarasaurus sp.) and one basal sauropodomorph dinosaur individual (Plateosaurus engelhardti). Using these estimates, we establish allometries between body mass and each of these traits and compare these to extant taxa. Growth models considered for each dinosaur individual were the von Bertalanffy model, the Gompertz model, and the logistic model (LGM), all of which have inherently fixed inflection points, and the Chapman-Richards model in which the point is not fixed. We use the arithmetic mean of the age at the inflection point and of the age at which 90% of asymptotic mass is reached to assess respectively the age at sexual maturity or the age at onset of reproduction, because unambiguous indicators of maturity in Sauropodomorpha are lacking. According to an AIC-based model selection process, the LGM was the best model for our sauropodomorph sample. Allometries established are consistent with literature data on other Sauropodomorpha. All Sauropodomorpha reached full size within a time span similar to scaled-up modern mammalian megaherbivores and had similar maximum growth rates to scaled-up modern megaherbivores and ratites, but growth rates of Sauropodomorpha were lower than of an average mammal. Sauropodomorph ages at death probably were lower than that of average scaled-up ratites and megaherbivores. Sauropodomorpha were older at maturation than scaled-up ratites and average mammals, but younger than scaled-up megaherbivores.

Overview of the Aetosaurs

Desojo, J. B., Heckert, A. B., Martz, J. W., Parker, W. G., Schoch, R. R., Small, B. J., and T. Sulej. 2013. Aetosauria: a clade of armoured pseudosuchians from the Upper Triassic continental beds; From Nesbitt, S. J., Desojo, J. B., and R. B. Irmis (eds.) Anatomy, Phylogeny and Palaeobiology of Early Archosaurs and their Kin, Geological Society Special Publication 379: doi:10.1144/SP379.17

Abstract -
Aetosauria is a clade of obligately quadrupedal, heavily armoured pseudosuchians known from Upper Triassic (late Carnian–Rhaetian) strata on every modern continent except Australia and Antarctica. As many as 22 genera and 26 species ranging from 1 to 6 m in length, and with a body mass ranging from less than 10 to more than 500 kg, are known. Aetosauroides scagliai was recently recovered as the most basal aetosaur, placed outside of Stagonolepididae (the last common ancestor of Desmatosuchus and Aetosaurus). Interrelationships among the basal aetosaurs are not well understood but two clades with relatively apomorphic armour – the spinose Desmatosuchinae and the generally wide-bodied Typothoracisinae – are consistently recognized. Paramedian and lateral osteoderms are often distinctive at the generic level but variation within the carapace is not well understood in many taxa, warranting caution in assigning isolated osteoderms to specific taxa. The aetosaur skull and dentition varies across taxa, and there is increasing evidence that at least some aetosaurs relied on invertebrates and/or small vertebrates as a food source. Histological evidence indicates that, after an initial period of rapid growth, lines of arrested growth (LAGs) are common and later growth was relatively slow. The common and widespread Late Triassic ichnogenus Brachychirotherium probably represents the track of an aetosaur.

Two New Aetosaur Papers Including a New Taxon, Stenomyti huangae, from the Chinle Formation of Colorado

Taborda, J. R. A., Cerda, I. A., and J. B. Desojo. 2013. Growth curve of Aetosauroides scagliai Casamiquela 1960 (Pseudosuchia: Aetosauria) inferred from osteoderm histology. From Nesbitt, S. J., Desojo, J. B., and R. B. Irmis (eds.), Anatomy, Phylogeny and Palaeobiology of Early Archosaurs and their Kin Geological Society Special Publications 379. doi:10.1144/SP379.19

Abstract - Recent palaeohistological studies on paramedian osteoderms of aetosaurs revealed the presence of growth lines (lines of arrested growth or LAGs) and a minimal or nonexistent secondary remodelling in the bone matrix of these elements. This feature allows the age of individuals to be estimated through growth line count. In the present contribution we study the growth curve of the South American aetosaur Aetosauroides scagliai. We estimated the age (obtained from LAG counting) and body size (body length and body mass were used as
proxies) of different aetosaur specimens in order to reconstruct the growth curve of the South American species. The data obtained for Aetosauroides scagliai were compared with that of other aetosaurs, such as Neoaetosauroides engaeus, Aetosaurus ferratus, Aetobarbakinoides brasiliensis, Typothorax coccinarum andParatypothorax sp. Our results indicate that, if body length is considered as proxy, all studied aetosaur specimens have a similar or almost identical growth rate. However, important variations arose among aetosaur taxa if body mass is considered as proxy, which would be related to a body morphology ranging from slender (e.g. Aetobarbakinoides brasiliensis) to very wide (Typothorax coccinarum) morphotypes. In comparison with extant pseudosuchians (i.e. crocodylians), Aetosauroides scagliai possesses a relatively lower growth rate.

Small, B. J., and J. W. Martz. 2013. A new aetosaur from the Upper Triassic Chinle Formation of the Eagle Basin, Colorado, USA.: From Nesbitt, S. J., Desojo, J. B., and R. B. Irmis (eds.), Anatomy, Phylogeny and Palaeobiology of Early Archosaurs and their Kin Geological Society Special Publications 379 doi:10.1144/SP379.18

Abstract - A small aetosaur skull and skeleton and referred material from the Chinle Formation, Eagle Basin of Colorado, USA, is described as a new taxon, Stenomyti huangae gen. et sp. nov, distinguished from other aetosaurs by the following autapomorphies: three premaxillary teeth; four palpebrals; pronounced midline ridge on frontals and parietals; paired ridges flanking midline ridge on parietal and frontal; exclusion of quadratojugal from ventral margin of skull by contact between jugal and quadrate; exclusion of postorbital from infratemporal fenestra; infratemporal fenestra a horizontally oriented oval that embays the posterior edge of the jugal; retroarticular process longer than distance between articular glenoid and posterior edge of external mandibular fenestra; oval to irregularly shaped ventral osteoderms that do not contact each other. Paramedian and lateral osteoderms of S. huangae are nearly identical to those of Aetosaurus ferratus, and other shared cranial characters suggest that
these taxa are closely related and lie outside the clade Typothoracisinae + Desmatosuchinae. This discovery indicates that other reports of Aetosaurus across Laurasia based on osteoderms should be reassessed. Similar confusion with the osteoderms of other non-typothoracisine/desmatosuchine aetosaurs such as Aetosauroides, Stagonolepis and Calyptosuchus suggests that osteoderms are not always reliable taxonomic indicators.


Dental Microwear of the Late Triassic Dinosauriform Silesaurus opolensis

Kubo, T., and M. O. Kubo. 2013. Dental microwear of a Late Triassic dinosauriform, Silesaurus opolensis. Acta Palaeontologica Polonica (in press).
doi:
http://dx.doi.org/10.4202/app.2013.0027

Abstract - Silesaurus opolensis belongs to Silesauridae, the closest sister group
to dinosaurs. The present study analyzed the dental  microwear patterns of Silesaurus opolensis. Low pit-to-scratch ratios imply they did not feed on hard objects. Unimodal distributions of both wear-facet and non-facet scratch orientations indicate simple orthal jaw movement. Scratch orientation and density differ between microscopic regions in Silesaurus, and unlike hadrosaurid dinosaurs, the microwear patterns of small areas are not identical to those of whole teeth.

Analysis of Triassic Archosauriform Trackways

Kubo, T. and M. O. Kubo. 2013. Analysis of Triassic archosauriform trackways: difference in stride/foot ratio between dinosauromorphs and other archosauriforms. Palaios 28: 259-265 doi:10.2110/palo.2012.p12-099r
Abstract - Fossilized trackways have rarely been analyzed quantitatively to examine major trends and patterns in evolution despite their potential utility, especially in understanding locomotory evolution. In the present study, trackways of Triassic archosauriforms were analyzed. The analyses showed foot and stride lengths of archosauriforms increased from the Early to Middle Triassic, especially those of dinosauromorphs, which tripled. Dinosauromorphs were much smaller in foot length and stride length compared to other archosauriforms during
the Early Triassic. They reached similar stride length compared with other archosauriforms during the Middle Triassic and similar foot length in the Late Triassic. Stride/foot ratio is significantly higher in dinosauromorphs compared to other archosauriforms throughout the Triassic. This relatively long stride length of dinosauromorphs is attributed to either faster speed or higher relative hip height that was probably caused by their digitigrade foot posture. Analyses of trackway data sets, especially in combination with precise trackmaker assignment and age determination, would bring us more thorough knowledge about locomotory evolution of tetrapods that complements body fossil evidence.

The Early Evolution of Synapsids

Brocklehurst, N., Kammerer, C. F., and J. Frobisch. 2013. The early evolution of synapsids, and the influence of sampling on their fossil record. Paleobiology 39:470-490. DOI: 10.1666/12049

Abstract - Synapsids dominated the terrestrial realm between the late Pennsylvanian and the Triassic.
Their early evolution includes some of the first amniotes to evolve large size, herbivory, and macropredators. However, little research has focused on the changes in diversity occurring during this early phase in their evolutionary history, with more effort concentrating on later events such the Permo-Triassic extinction. Here we assess synapsid diversity, at both the species and genus levels, between the Carboniferous (Moscovian) and the Middle Permian (Capitanian). A raw, taxic diversity (richness) estimate is generated, and we use two separate methods to correct for sampling biases in this curve. To remove the effect of anthropogenic sampling bias, we apply a recently published modification of the residual diversity method, and then generate a supertree, using matrix representation with parsimony to infer ghost lineages and obtain a phylogenetic diversity estimate. The general diversity pattern reflects the initial diversification of synapsids in the late Pennsylvanian and early Cisuralian, which was followed by an extinction event during the Sakmarian. Diversity recovered during the Artinskian and Kungurian, coinciding with the radiation of Caseidae, although other families begin to decline. A second extinction event occurred across the Kungurian/Roadian boundary, in which Edaphosauridae and Ophiacodontidae died out although Caseidae and Therapsida diversified. The sampling-corrected curves reveal further extinction during the Roadian, although therapsids were again unaffected. Pelycosaurian-grade synapsids survived during the Wordian and Capitanian, but were a minor part of an otherwise therapsid-dominated fauna. Evidence of significant anthropogenic sampling bias calls
into question previous diversity studies that have not employed sampling correction.

New Hypothesis on the Evolutionary Origin of the Turtle Shell (with video)

This recent early online paper has been getting a lot of attention lately regarding the origin of turtles and their phylogenetic relationships. There is also this associated video on YouTube depicting this new hypothesis of the evolution of the turtle shell.

Lyson, T. R., Bever, G. S., Scheyer, T. M., Hsiang, A. Y.,  and J. A. Gauthier. 2013. Evolutionary Origin of the Turtle Shell. Current Biology. doi: http://dx.doi.org/10.1016/j.cub.2013.05.003Abstract - The origin of the turtle shell has perplexed biologists for more than two centuries. It was not until Odontochelys semitestacea was discovered, however, that the fossil and developmental data could be synthesized into a model of shell assembly that makes predictions for the as-yet unestablished history of the turtle stem group. We build on this model by integrating novel data for Eunotosaurus africanus—a Late Guadalupian (~260 mya) Permian reptile inferred to be an early stem turtle. Eunotosaurus expresses a number of relevant characters, including a reduced number of elongate trunk vertebrae (nine), nine pairs of T-shaped ribs, inferred loss of intercostal muscles, reorganization of respiratory muscles to the ventral side of the ribs, (sub)dermal outgrowth of bone from the developing perichondral collar of the ribs, and paired gastralia that lack both lateral and median elements. These features conform to the predicted sequence of character acquisition and provide further support that E. africanusO. semitestacea, and Proganochelys quenstedti represent successive divergences from the turtle stem lineage. The initial transformations of the model thus occurred by the Middle Permian, which is congruent with molecular-based divergence estimates for the lineage, and remain viable whether turtles originated inside or outside crown Diapsida.

Revisiting the Dicynodonts of Western North America

Kammerer, C. F., Fröbisch, J., and Angielczyk, K. D. 2013. On the validity and phylogenetic position of Eubrachiosaurus browni, a kannemeyeriiform dicynodont (Anomodontia) from Triassic North America. PLoS ONE 8(5): e64203. doi:10.1371/journal.pone.0064203

Abstract - The large dicynodont Eubrachiosaurus browni from the Upper Triassic Popo Agie Formation of Wyoming is redescribed. Eubrachiosaurus is a valid taxon that differs from Placerias hesternus, with which it was previously synonymized, by greater anteroposterior expansion of the scapula dorsally and a very large, nearly rectangular humeral ectepicondyle with a broad supinator process. Inclusion of Eubrachiosaurus in a revised phylogenetic analysis of anomodont therapsids indicates that it is a stahleckeriid closely related to the South American genera Ischigualastia and Jachaleria. The recognition of Eubrachiosaurus as a distinct lineage of North American dicynodonts, combined with other recent discoveries in the eastern USA and Europe, alters our perception of Late Triassic dicynodont diversity in the northern hemisphere. Rather than being isolated relicts in previously therapsid-dominated regions, Late Triassic stahleckeriid dicynodonts were continuing to disperse and diversify, even in areas like western North America that were otherwise uninhabited by coeval therapsids (i.e., cynodonts).