Field of Science

Braincase of the Temnospondyl Gerrothorax from the Middle Triassic of Germany

Witzmann, F., Schoch, R. R., Hilger, A. and N. Kardjilov. 2011. Braincase, palatoquadrate and ear region of the plagiosaurid Gerrothorax pulcherrimus from the Middle Triassic of Germany. Palaeontology (early online). doi: 10.1111/j.1475-4983.2011.01116.x

Abstract - The complete neurocranium plus palatoquadrate of the plagiosaurid temnospondyl Gerrothorax pulcherrimus from the Middle Triassic of Germany is described for the first time, based on outer morphological observations and micro-CT scanning. The exoccipitals are strong elements with paroccipital processes and well-separated occipital condyles. Anterolaterally, the exoccipitals contact the otics, which are mediolaterally elongated and have massive lateral walls. The otics contact the basisphenoid, which shows well-developed sellar processes. Anteriorly, the basisphenoid is continuous with the sphenethmoid region. In its posterior portion, the sphenethmoid gives rise to robust, laterally directed laterosphenoid walls, a unique morphology among basal tetrapods. The palatoquadrate is extensively ossified. The quadrate portion overlaps the descending lamina of squamosal and ascending lamina of pterygoid anteriorly, almost contacting the epipterygoid laterally. The epipterygoid is a complex element and may be co-ossified with otics and laterosphenoid walls. It has a broad, sheet-like footplate and a horizontally aligned ascending process that contacts the laterosphenoid walls. The degree of ossification of the epipterygoid, however, is subject to individual variation obviously independent from ontogenetic changes. The stapes of Gerrothorax is a large, blade-like element that differs conspicuously from the plesiomorphic temnospondyl condition. It has a prominent anterolateral projection which has not been observed in other basal tetrapods. Morphology of neurocranium and palatoquadratum of Gerrothorax most closely resembles that of the Russian plagiosaurid Plagiosternum danilovi, although the elements are less ossified in the latter. The extensive endocranial ossification of Gerrothorax is consistent with the general high degree of ossification in the exo- and endoskeleton of this temnospondyl and supports the view that a strong endocranial ossification cannot be evaluated as a plesiomorphic character in basal tetrapods.

Disparity and Convergence in Bipedal Archosaur Locomotion

Bates, K. T., and E. R. Schachner. 2011. Disparity and convergence in bipedal archosaur locomotion. Journal of the Royal Society Interface (advance online publication) doi: 10.1098/​rsif.2011.0687

Abstract - This study aims to investigate functional disparity in the locomotor apparatus of bipedal archosaurs. We use reconstructions of hindlimb myology of extant and extinct archosaurs to generate musculoskeletal biomechanical models to test hypothesized convergence between bipedal crocodile-line archosaurs and dinosaurs. Quantitative comparison of muscle leverage supports the inference that bipedal crocodile-line archosaurs and non-avian theropods had highly convergent hindlimb myology, suggesting similar muscular mechanics and neuromuscular control of locomotion. While these groups independently evolved similar musculoskeletal solutions to the challenges of parasagittally erect bipedalism, differences also clearly exist, particularly the distinct hip and crurotarsal ankle morphology characteristic of many pseudosuchian archosaurs. Furthermore, comparative analyses of muscle design in extant archosaurs reveal that muscular parameters such as size and architecture are more highly adapted or optimized for habitual locomotion than moment arms. The importance of these aspects of muscle design, which are not directly retrievable from fossils, warns against over-extrapolating the functional significance of anatomical convergences. Nevertheless, links identified between posture, muscle moments and neural control in archosaur locomotion suggest that functional interpretations of osteological changes in limb anatomy traditionally linked to postural evolution in Late Triassic archosaurs could be constrained through musculoskeletal modelling.

New Material of the Cynodont Dadadon isaloi from the Triassic of Madagascar

Ranivoharimanana, L., Kammerer, C. F., John J. Flynn, J. J., and A. R. Wyss. 2011. New material of

Abstract - New material of the traversodontid cynodont Dadadon isaloi from the Triassic of southwestern Madagascar is described. The new material consists of a complete, well-preserved skull (FMNH PR 2232) and an unassociated, partial lower jaw (UA 10608). The new material reveals several novel aspects of Dadadon's morphology. Newly recognized autapomorphies that diagnose Dadadon include a fourth upper incisor with posterior accessory cusp, deep interorbital depressions confined to the frontals, and a very tall, robust mid-frontal ridge. Dadadon can further be distinguished from the similar traversodontids Massetognathus and Santacruzodon by the presence of shorter, broader prefrontals with prominent dorsal depressions, robust anterolateral processes overhanging the orbits, a single cusp in the anterior cingulum of the upper postcanines, and relatively elongate, striated, conical upper incisors. In a revised phylogenetic analysis incorporating data from the new specimens, Dadadon is recovered in a clade with Massetognathus and Santacruzodon. This clade is the sister taxon to the well-supported traversodontid subclade Gomphodontosuchinae. The ‘basal Isalo II’ cynodont fauna from Madagascar is more similar in composition to that of South America than to mainland Africa, although this is probably attributable to the lack of Ladinian–Carnian therapsid fossils on the mainland rather than an actual biogeographic pattern.
Dadadon isaloi (Cynodontia, Traversodontidae) from the Triassic of Madagascar. Journal of Vertebrate Paleontology 31:1292-1302. DOI:10.1080/02724634.2011.618154

Osteohistology of Some Triassic Archosauromorphs

Botha-Brink, J., and R. M. H. Smith. 2011. Osteohistology of the Triassic archosauromorphs Prolacerta, Proterosuchus, Euparkeria, and Erythrosuchus from the Karoo Basin of South Africa. Journal of Vertebrate Paleontology 31:1238-1254. DOI:10.1080/02724634.2011.621797

Abstract - The South African non-archosauriform archosauromorph Prolacerta and the archosauriforms Proterosuchus, Erythrosuchus, and Euparkeria were important constituents of the Early to early Middle Triassic Karoo ecosystem following the end-Permian mass extinction. We present new data on the osteohistology of these stem archosaurs and provide insight into their paleobiology. Bone tissues of the Early Triassic Prolacerta contain a poorly defined fibro-lamellar complex, with parallel-fibered bone in some regions, whereas the contemporaneous Proterosuchus exhibits rapidly forming uninterrupted fibro-lamellar bone early in its ontogeny, which becomes slow forming lamellar-zonal bone with increasing age. The early Middle Triassic Erythrosuchus deposited highly vascularized, uninterrupted fibro-lamellar bone throughout ontogeny, whereas the growth of the contemporaneous Euparkeria was relatively slow and cyclical. When our data are combined with those of previous studies, preliminary results reveal that Early and Middle Triassic non-crown group archosauromorphs generally exhibit faster growth rates than many of those of the Late Triassic. Early rapid growth and rapid attainment of sexual maturity are consistent with life history expectations for taxa living in the unpredictable conditions following the end-Permian mass extinction. Further research with larger sample sizes will be required to determine the nature of the environmental pressures on these basal archosaurs.

Redescription of a Nearly Complete Skull of Plateosaurus from the Late Triassic of Germany

Prieto-Márquez, A., and M. A. Norell. 2011. Redescription of a nearly complete skull of Plateosaurus (Dinosauria: Sauropodomorpha) from the Late Triassic of Trossingen (Germany). American Museum Novitates 3727 :1-58. 
doi:
http://www.bioone.org/doi/abs/10.1206/3727.2

Abstract - The nearly complete, disarticulated skull of AMNH FARB 6810, a specimen of the basal sauropodomorph Plateosaurus collected in 1925 from the Norian (Late Triassic) strata of the Knollenmergel beds of Trossingen (Germany), is redescribed. This study supports referral of AMNH FARB 6810 to P. erlenbergiensis on the basis of the following characters: occipital condyle above level of parasphenoid; basisphenoid with transverse, subvertical lamina extending between basipterygoid processes, with ventrally projecting median process; and peglike process projecting medially from the middle of the palatine. Furthermore, P. longiceps is regarded a junior synonym of P. erlenbergiensis because the type specimen of the latter is diagnostic (displaying the above-noted apomorphies of the braincase and palatine) and, chronologically, P. erlenbergiensis has priority over P. longiceps.

Did An Extraterrestrial Impact Hasten the End-Triassic Extinction On Land?

This is a interesting news article in Nature examining work by Drs. Paul Olsen and Dennis Kent on the possibility that the Rochechouart impact in France may have had an adverse effect on global terrestrial populations around 200 million years ago. The article also includes an excellent new Triassic scene by Victor O. Leshyk, which features Redondavenator and Redondasaurus from the Upper Triassic Redonda Formation of New Mexico. There is also a Typothorax-like aetosaur in the background for armodillodile fans.

Pampadromaeus barberenai, a New Basal Sauropodomorph from the Late Triassic of Brazil

For those of you who were at SVP this year, this is the new dinosaur taxon from the Triassic of Brazil that Max Langer presented on.

Cabreira, S. F., Schultz, C. L., Bittencourt, J. S., Soares, M. B., Fortier, D. C., Silva, L. R., and M. C. Langer. 2011. New stem-sauropodomorph (Dinosauria, Saurischia) from the Triassic of Brazil. Naturwissenschaften (advance online publication) DOI: 10.1007/s00114-011-0858-0

Abstract - Post-Triassic theropod, sauropodomorph, and ornithischian dinosaurs are readily recognized based on the set of traits that typically characterize each of these groups. On the contrary, most of the early members of those lineages lack such specializations, but share a range of generalized traits also seen in more basal dinosauromorphs. Here, we report on a new Late Triassic dinosaur from the Santa Maria Formation of Rio Grande do Sul, southern Brazil. The specimen comprises the disarticulated partial skeleton of a single individual, including most of the skull bones. Based on four phylogenetic analyses, the new dinosaur fits consistently on the sauropodomorph stem, but lacks several typical features of sauropodomorphs, showing dinosaur plesiomorphies together with some neotheropod traits. This is not an exception among basal dinosaurs, the early radiation of which is characterized by a mosaic pattern of character acquisition, resulting in the uncertain phylogenetic placement of various early members of the group.

Leyesaurus marayensis, a New Basal Sauropodomorph from Argentina and a Reanalysis of the Paleobiogeography of the Massospondylids

Apaldetti, C., Martinez, R. N., Alcober, O. A., and D. Pol. 2011. A New Basal Sauropodomorph (Dinosauria: Saurischia) from Quebrada del Barro Formation (Marayes-El Carrizal Basin), Northwestern Argentina.PLoS ONE 6(11): e26964. doi:10.1371/journal.pone.0026964

BackgroundArgentinean basal sauropodomorphs are known by several specimens from different basins; Ischigualasto, El Tranquilo, and Mogna. The Argentinean record is diverse and includes some of the most primitive known sauropodomorphs such as Panphagia and Chromogisaurus, as well as more derived forms, including several massospondylids. Until now, the Massospondylidae were the group of basal sauropodomorphs most widely spread around Pangea with a record in almost all continents, mostly from the southern hemisphere, including the only record from Antarctica.

Methodology/Principal FindingsWe describe here a new basal sauropodomorph, Leyesaurus marayensis gen. et sp. nov., from the Quebrada del Barro Formation, an Upper Triassic-Lower Jurassic unit that crops out in northwestern Argentina. The new taxon is represented by a partial articulated skeleton that includes the skull, vertebral column, scapular and pelvic girdles, and hindlimb. Leyesaurus is diagnosed by a set of unique features, such as a sharply acute angle (50 degrees) formed by the ascending process of the maxilla and the alveolar
margin, a straight ascending process of the maxilla with a longitudinal ridge on its lateral surface, noticeably bulging labial side of the maxillary teeth, greatly elongated cervical vertebrae, and proximal
articular surface of metatarsal III that is shelf-like and medially deflected. Phylogenetic analysis recovers Leyesaurus as a basal sauropodomorph, sister taxon of Adeopapposaurus within the Massospondylidae. Moreover, the results suggest that massospondylids achieved a higher diversity than previously thought.

Conclusions/SignificanceOur phylogenetic results differ with respect to previous analyses by rejecting the massospondylid affinities of some taxa from the northern hemisphere (e.g., Seitaad, Sarahsaurus). As a result, the new taxon
Leyesaurus, coupled with other recent discoveries, suggests that the diversity of massospondylids in the southern hemisphere was higher than in other regions of Pangea. Finally, the close affinities of Leyesaurus with the Lower Jurassic Massospondylus suggest a younger age for the Quebrada del Barro Formation than previously postulated.

New information on the Protorosaurian Reptile Macrocnemus fuyuanensis from the Triassic of China

The new issue of JVP is out:

Jiang, D.-Y., Rieppel, O., Fraser, N. C., Motani, R., Hao, W.-C., Tintori, A., Sun, Y.-L., and Z.-Y. Sun. 2011. New information on the protorosaurian reptile Macrocnemus fuyuanensis Li et al., 2007, from the Middle/Upper Triassic of Yunnan, China. Journal of Vertebrate Paleontology 31: 2011-1237, DOI:10.1080/02724634.2011.610853

Abstract - A new specimen of the protorosaur Macrocnemus fuyuanensis, from the Zhuganpo Member of the Falang Formation at Fuyuan (Yunnan Province, southwestern China), is described and compared with Macrocnemus bassanii. The new specimen is the first in the genus Macrocnemus that clearly shows details of the preorbital region of the skull. A large, plate-like lacrimal is located in front of the tall, columnar prefrontal that defines the anterior margin of the orbit. A longitudinally oriented nasal groove extends along the anterior two-thirds of the snout, accommodating the external naris at its anterior part. A similar preorbital depression has previously been described for Dinocephalosaurus and it is also reported here for the first time in Tanystropheus. The new specimen confirms the status of Macrocnemus fuyuanensis as a species distinct from Macrocnemus bassanii on the basis of a humerus that significantly exceeds the radius in length. The occurrence of both Macrocnemus and Tanystropheus in southwestern China further underscores the close faunal affinities of the eastern and western Tethyan realms during the Middle and early Late Triassic.

Taphonomic Effects on the Stratigraphic Ranges of Rare Taxa in the Chinle Formation of Arizona

Loughney, K. M., Fastovsky, D. E., and W. G. Parker. 2011. Vertebrate fossil preservation in blue paleosols from the Petrified Forest National Park, Arizona, with implications for vertebrate biostratigraphy in the Chinle Formation. Palaios 26:700-719.

Abstract - Exposures of the Chinle Formation in Petrified Forest National Park (PEFO), Arizona, preserve one of the most important Upper Triassic terrestrial faunal assemblages in the world: in it are found key elements in the global and regional correlation of continental deposits of Upper Triassic age. Rare components of the Chinle Formation faunal assemblage, including dinosaurs and small-bodied amniotes, appear to be mostly restricted to distinctive blue-colored horizons observed at only a few sites in PEFO. The blue sites represent paleosols formed in fine-grained, abandoned channel fills and contrast markedly with red-colored floodplain deposits and paleosols that characterize most fossil localities in the Chinle Formation. The distinctive blue color is interpreted as a weathered feature of hydromorphically reduced iron. The coincidence of rare taxa and sites bearing the blue-colored paleosols suggests that the stratigraphic positions of the sites and the rare taxa they contain appear to relate to fluvial sequence tracts in PEFO and may not reflect the true stratigraphic ranges of these taxa.