Field of Science

New Neopterygian Fishes from the Chinle Formation of Utah

This is an important new paper describing some new fishes from the Chinle Formation of Utah. Well-preserved fish are rare throughout much of the Chinle and relatively understudied in previous decades.  Nonetheless, they were important constituents of the Late Triassic biota, and much material goes unrecognized because many Chinle Formation workers (myself included) are one, unfamiliar with the fish fossil record, and two, the taxonomy of this group is in serious need of revision.  Sarah's new work and phylogenentic study is a huge step forward in rectifying these problems. We should all start paying more attention.

Gibson, S. Z. 2013. Biodiversity and Evolutionary History of Lophionotus (Neopterygii: Semionotiformes) from the Western United States. Copeia 2013:582-603. DOI: 10.1643/CI-12-028

Abstract - Two species of the neopterygian genus †Lophionotus Gibson, 2013, are described. Specimens of †Lophionotus chinleana, new species, were previously and recently collected from freshwater deposits in the Upper Triassic Chinle Formation of Lisbon Valley, southeastern Utah. †Semionotus kanabensis Schaeffer and Dunkle, 1950, from lacustrine deposits in the Lower Jurassic Moenave Formation of southwestern Utah, is herein redescribed and attributed to the genus †Lophionotus, based on shared characters, including the infraorbital in the posteroventral corner of the orbit being expanded and contacting the anterior ramus of the preoperculum. Both new species of †Lophionotus are distinct from †L. sanjuanensis Gibson, 2013, in that they lack a postcranial hump, deep body, dense tuberculation, and ventrally expanded preoperculum. The addition of two new species lends to a revised generic description of the genus †Lophionotus. A phylogenetic analysis infers a monophyletic †Lophionotus sister to the genus †Semionotus, and †Lophionotus is placed within the family †Semionotidae within †Semionotiformes.

Ice Archosauromorph


 Recent retreat of ancient ice sheets from western Virginia has revealed the frozen exquisitely preserved remains of a phytosaurian archosaur. The specimen appears to be of the fully crested type, similar to Nicrosaurus kapffi, previously only known from Germany. As the photos below demonstrate, even details of the soft tissue are preserved giving us amazing insight of this animal such as proportions, posture, and that it had bulgy eyeballs. 
 



 A close-up of the pes shows that digit four is the longest, supporting the hypothesis that the ichnoform Apatopus is indeed the track of phytosaurians.


Discoverers Michelle Stocker and Sterling Nesbitt are taking measurements and describing the new find before the Spring thaw, hopefully publishing the results soon.  In the meantime they are also eagerly awaiting what other rare forms may be exposed as these thick deposits of eastern ice finally retreat.

 




Triassic Period: Reptiles Rule. Video from the Discovery Channel.

I assume this is supposed to be the southwest U.S. during the Late Triassic, but there is a hodge-podge of animals from different ages. Still pretty cool though; however, I wish the aetosaur and photosaur were on the scene a little longer, and where is the ubiquitous Postosuchus?

http://www.discovery.com/video-topics/other/dinosaur-videos/triassic-period-reptiles-rule.htm

Large Body Size in Non-dinosaurian Dinosauromorphs - Evidence from a Large Silesaurid from Late Triassic of Tanzania

Barrett, P. M., Nesbitt, S. J., and B. R. Peecook. 2014. A large-bodied silesaurid from the Lifua Member of the Manda beds (Middle Triassic) of Tanzania and its implications for body-size evolution in Dinosauromorpha. Gondwana Research (accepted manuscript). http://dx.doi.org/10.1016/j.gr.2013.12.015

Abstract
- Many dinosaur lineages were characterised by wide ranges of body-size, ranging from taxa that were <1 m in length to the largest of all terrestrial vertebrates. On the other hand, the closest relatives of dinosaurs, the non-dinosaurian dinosauromorphs, such as Marasuchus and lagerpetids, were small-bodied animals with little variation in body-size. Here, we describe a partial femur of an unexpectedly large-bodied silesaurid (non-dinosaurian dinosauriform) from the Lifua Member of the Manda beds (?late Anisian) from southwestern Tanzania. This specimen (NHMUK R16303) is estimated to have had a femoral length of approximately 345 mm, which exceeds that of many Triassic and Lower Jurassic dinosaurs, and is either a large individual of the contemporary Asilisaurus kongwe or represents a new and otherwise unknown silesaurid taxon. In either case, it shows that body-size increases were more prevalent among early dinosauromorphs than realised previously. Moreover, silesaurid size increase occurred in parallel with that in early dinosaurs, alongside the convergent acquisition of other features related to locomotion and herbivory. However, Late Triassic faunas including large-bodied sauropodomorph and theropod dinosaurs lack similarly-sized non-dinosaurian dinosauromorphs, whereas the Lifua Member fauna includes both a large silesaurid and the early ?dinosaur Nyasasaurus, which overlapped in size.

New Open Access Paper Discussing the Rise of Dinosaurs

Benton, M.J., Forth, J., and M.C. Langer. 2014. Models for the rise of dinosaurs. Modern Biology 24:R87-R95. doi:10.1016/j.cub.2013.11.063

Abstract - Dinosaurs arose in the early Triassic in the aftermath of the greatest mass extinction ever and became hugely successful in the Mesozoic. Their initial diversification is a classic example of a large-scale macroevolutionary change. Diversifications at such deep-time scales can now be dissected, modelled and tested. New fossils suggest that dinosaurs originated early in the Middle Triassic, during the recovery of life from the devastating Permo-Triassic mass extinction. Improvements in stratigraphic dating and a new suite of morphometric and comparative evolutionary numerical methods now allow a forensic dissection of one of the greatest turnovers in the history of life. Such studies mark a move from the narrative to the analytical in macroevolutionary research, and they allow us to begin to answer the proposal of George Gaylord Simpson, to explore adaptive radiations using numerical methods.

The Foot of Poposaurus gracilis, Further Convergence with Theropod Dinosaurs

....and the answer to the question we've all been wondering...what type of footprint would Poposaurus have left? It appears that Poposaurus  probably could have left a Grallator-like track.

Farlow, J. O., Schachner, E. R., Sarrazin, J. C., Klein, H., and P. J. Currie. 2014. Pedal Proportions of Poposaurus gracilis: Convergence and Divergence in the Feet of Archosaurs. The Anatomical Record, Early View. DOI: 10.1002/ar.22863.

Abstract - The crocodile-line basal suchian Poposaurus gracilis had body proportions suggesting that it was an erect, bipedal form like many dinosaurs, prompting questions of whether its pedal proportions, and the shape of its footprint, would likewise “mimic” those of bipedal dinosaurs. We addressed these questions through a comparison of phalangeal, digital, and metatarsal proportions of Poposaurus with those of extinct and extant crocodile-line archosaurs, obligate or facultatively bipedal non-avian dinosaurs, and ground birds of several clades, as well as a comparison of the footprint reconstructed from the foot skeleton of Poposaurus with known early Mesozoic archosaurian ichnotaxa. Bivariate and multivariate analyses of phalangeal and digital dimensions showed numerous instances of convergence in pedal morphology among disparate archosaurian clades. Overall, the foot of Poposaurus is indeed more like that of bipedal dinosaurs than other archosaur groups, but is not exactly like the foot of any particular bipedal dinosaur clade. Poposaurus likely had a digitigrade stance, and its footprint shape could have resembled grallatorid ichnotaxa, unless digit I of the foot of Poposaurus commonly left an impression.

Bone Histology of Phytosaur, Aetosaur, and Other Archosauriform Osteoderms

Just in time for Christmas...

Scheyer, T. M., Desojo, J. B., and I. A. Cerda. 2013. Bone histology of phytosaur, aetosaur, and other archosauriform osteoderms (Eureptilia, Archosauromorpha). Anatomical Record (early view) DOI: 10.1002/ar.22849

Abstract -
As in other archosauriforms, phytosaurs and aetosaurs are characterized by the presence of well-developed osteoderms. Here we provide a comparative study on the microstructure of phytosaur (five taxa) and aetosaur (thirteen taxa) osteoderms. For outgroup comparison, we sampled osteoderms of the sister taxon to Aetosauria, Revueltosaurus callenderi, and the doswelliid Jaxtasuchus salomoni. Phytosaur, aetosaur, and Jaxtasuchus osteoderms are composed of a diploe structure, whereas the Revueltosaurus osteoderm microanatomy is more compact. The external cortex of phytosaurs, Revueltosaurus and Jaxtasuchus osteoderms is mainly composed of parallel-fibered bone. In aetosaurs, the external cortex mainly consists of lamellar bone, with lines of resorption within the primary bone indicating successive cycles of bone erosion and deposition. The basal cortex in all the specimens is composed of parallel-fibered bone, with the cancellous internal core being more strongly developed in aetosaurs than in phytosaurs. Woven or fibro-lamellar bone was recorded in both phytosaurian and aetosaurian taxa, as well as in Jaxtasuchus. Structural fibers, which at least partly suggest metaplastic origin, were only recorded in the internal core of two phytosaurs and in the
basal cortex of one aetosaur. Osteoderm thickness and cancellous to compact bone ratios appear to be subject to ontogenetic change. Minimum growth mark counts in osteoderms sampled indicate that some aetosaurs and phytosaurs lived for at least two decades. Bone microstructures are more uniform in phytosaur osteoderms and show a higher level of disparity among aetosaur osteoderms, and at least in the latter, histological features are potentially apomorphic for species/genus level.

Standardizing Triassic Stratigraphic Nomenclature in New Mexico

This is a new paper written by a group of geologists who are largely responsible for conducting much of the current geological mapping in New Mexico, and is an attempt to standardize the nomenclature used for Phanerozoic rocks especially the Triassic. Key recommendations regarding the Triassic rocks are abandonment of the Chinle as a Group and keeping it at the formation level, removal of the Dockum from the "Chinle Group" and reinstatement as the Dockum Group as traditionally used, and a suggestion where to divide strata between the Chinle and Dockum.  Consideration of the Chinle as a group and subsuming the Dockum has been controversial and never fully accepted since it was first proposed in the early 1990s. Thus, this paper suggests abandonment of much of the nomenclature proposed by Spencer Lucas and colleagues over the last couple of decades.

Cather, S. M., Zeigler, K. E., Mack, G. H., and S. A. Kelley. 2013. Toward standardization of Phanerozoic stratigraphic nomenclature in New Mexico. Rocky Mountain Geology 48:101-124. doi:10.2113/gsrocky.48.2.101
 
Abstract - Nomenclature for Phanerozoic strata in New Mexico has been rapidly evolving, but not all proposed changes have been widely accepted. From a perspective of geologic mapping, we evaluate some recent nomenclatural proposals for Pennsylvanian, Permian, Triassic, Jurassic, and Paleogene units. Because of the long shelf-life of geologic quadrangle maps and the desirability of minimizing nomenclatural diversity among them, we present guidelines with which we argue for a conservative approach to changes in stratigraphic nomenclature.

Redescription of "Paleorhinus" (Phytosauria) Specimens from Germany

Butler, R. J., Rauhut, O. W. M., Stocker, M. R., and R. Bronowicz. 2013. Redescription of the phytosaurs Paleorhinus (‘Francosuchus’) angustifrons and Ebrachosuchus neukami from Germany, with implications for Late Triassic biochronology. Zoological Journal of the Linnean Society Early View. DOI: 10.1111/zoj.12094

 
Abstract - Phytosaurs are a diverse and morphologically distinctive clade of superficially crocodile-like archosauriforms that had a near global distribution during the Late Triassic. Because their remains are among the most abundant vertebrate remains recovered in many Upper Triassic terrestrial formations, phytosaurs are used extensively in long-range biochronological and biostratigraphic correlations. The biochronologically oldest and earliest branching known phytosaurs include an array of nominal species from the early Late Triassic of the United States, Germany, Poland, Morocco, and India that have been synonymized within the genus Paleorhinus, and subsequently used to define a global ‘Paleorhinus biochron’. However, recent phylogenetic work suggested that the North American species previously referred to Paleorhinus are paraphyletic. Here, we reassess the systematics and anatomy of putative specimens of Paleorhinus from southern Germany. Two well-preserved basal phytosaur skulls from the Blasensandstein (Carnian) of Bavaria form the holotypes of Francosuchus angustifrons and Ebrachosuchus neukami, both of which were synonymized with Paleorhinus by previous workers. We demonstrate that Francosuchus angustifrons shares unique synapomorphies with specimens referred to Paleorhinus bransoni from the Late Triassic of Texas, and thus refer the species to Paleorhinus. By contrast, the longirostrine Ebrachosuchus is highly distinctive in morphology, and our new cladistic analysis of Phytosauria demonstrates that it represents a valid taxon that is more closely related to Phytosauridae than to Paleorhinus. We provide the first autapomorphy-based support for a monophyletic but restricted Paleorhinus (supported by a nodal row on the jugal, and low paired ridges on the squamosal) and confirm that previous broader conceptions of Paleorhinus are likely to be paraphyletic.

Mammal-like Tooth from the Upper Triassic of Poland

 Świło, M., Niedźwiedzki, G., and T. Sulej. 2013. Mammal-like tooth from the Upper Triassic of Poland. Acta Palaeontologica Polonica Accepted Manuscript doi:http://dx.doi.org/10.4202/app.00016.2013.

Abstract - Triassic discoveries have extended the record of near-mammals (Mammaliaformes) back to the Norian, about 215 Ma, and reveal a significant diversity of Late Triassic (Norian-Rhaetian) forms. We now add to this Late Triassic diversity a nearly complete double-rooted right lower molariform tooth (ZPAL V.33/734) from the Polish Upper Triassic that is significant because it comes from uppermost Norian–lower Rhaetian rocks and is the first discovery of a mammal-like tooth in the Mesozoic of Poland. The described tooth shows transitional dental morphology between advanced cynodonts and mammaliaforms and it appears to represent a basal mammaliaform (Hallautherium genus), probably belonging to Morganucodonta.

Colorado Plateau Coring Project

Coring is currently underway in Petrified Forest National Park targeting the Chinle and Moenkopi Formations.

You can read about the project and follow the links to the main project page and daily blog from here. The main page is here.

There is also a Facebook page with numerous updates.

Please check this project out. The beautiful logo was designed by Steven Seppi.



A New Specimen of the Middle Triassic Archosauriform Shansisuchus shansisuchus from China

Wang, R., Xu, S., , Wu, X., Li, C., and S. Wang. 2013. A New Specimen of Shansisuchus shansisuchus Young, 1964 (Diapsida: Archosauriformes) from the Triassic of Shanxi, China. Acta Geologica Sinica (English Edition) 87:1185-1197 DOI: 10.1111/1755-6724.12145

Abstract - Shansisuchus shansisuchus Young, 1964 was restudied on the basis of a new specimen. Some anatomical features that were either briefly or not described at all in the original study were detailed. The new specimen not only provides further information on the skull anatomy and the vertebral column but also expands the range of the geographical distribution of the taxon. With new information, the diagnosis of S. shansisuchus was emended and its phylogenetic relationships were further analyzed. S. shansisuchus differs from other archosauriforms primarily in the presence of a large subnarial fenestra anterior to the antorbital fenestra, tongue- n-groove articulations between the ascending process of the premaxilla and nasal and between the premaxilla and maxilla, a tall and posterodorsally directed ascending process of the maxilla, a knee-shaped process of the postorbital projecting into the orbit, a broad descending process of squamosal distally well forked and a large, deeply bow-shaped intercentrum tightly anchoring/capping the sharp ventral edges of two neighboring centra together in cervical and at least first eight dorsal vertebrae. With additional information derived from the new specimen, the phylogenetic relationships of S. shansisuchus were reanalyzed; it is closely related to Erythrosuchus-Vjushkovia clade.

Two New Late Triassic Phytosaur Papers

Stocker, M. R.. 2013. A new taxonomic arrangement for Paleorhinus scurriensis. Earth and Environmental Science Transactions of the Royal Society of Edinburgh (advance online publication)DOI: http://dx.doi.org/10.1017/S1755691013000340

Abstract - The paraphyletic genus ‘Paleorhinus’ is understood currently as a cosmopolitan phytosaur taxon from the Late Triassic. There is no consensus regarding the number of species of ‘Paleorhinus,’ with multiple species and genera synonymised into a single genus or even a single species at various points in its published history. The taxonomy is confounded by historical descriptions without the benefit of comparisons to more recently collected specimens, emphasis on plesiomorphic cranial morphology as diagnostic features of the genus,
and lack of cladistic analyses. When included in a recent explicitly cladistic phylogenetic analysis, the holotype of ‘Paleorhinusscurriensis (TTU P-00539) was found to be the earliest-branching phytosaur with respect to other North American specimens previously referred to ‘Paleorhinus,’ and is generically distinct from Paleorhinus. ‘Paleorhinusscurriensis differs from all known phytosaurs in five unambiguous characters: basitubera widely separated mediolaterally; ridge present on lateral surface of jugal; thickened shelf present along posteroventral edge of expanded pterygoid-quadrate wing; ‘septomaxillae’ separated and excluded from internarial septum; and nasal swelling present posterior to posterior borders of nares. This detailed morphological description of an early-branching phytosaur taxon is a first step towards resolving long-standing issues surrounding specific anatomical features and relationships among early members of the clade.




Hungerbühler, A., Mueller, B., Chatterjee, S., and D. P. Cunningham. 2013. Cranial anatomy of the Late Triassic phytosaur Machaeroprosopus, with the description of a new species from West Texas. Earth and Environmental Science Transactions of the Royal Society of Edinburgh (advance online publication) DOI: http://dx.doi.org/10.1017/S1755691013000364

Abstract - The skull anatomy of a new species of the phytosaur Machaeroprosopus is described for the first time on the basis of two specimens from the Upper Triassic Cooper Canyon Formation of Texas. Additional information is provided by a third specimen referred to Machaeroprosopus sp. A paranasal bone, an additional paired element of the narial region, is identified. Important new data are presented for the braincase, including the morphology of the epipterygoid and presphenoid, an anterior process of the prootic, an anteroventral process of the laterosphenoid, and a parasphenoid process. Machaeroprosopus lottorum n. sp. is characterised by four apomorphies: a supratemporal fenestra closed on the skull roof with beveled anterior rim, a comparatively short squamosal, a flat and rugose narial rim, and medially extended palatines that come close to form an ossified secondary palate. With respect to the supratemporal fenestra, the supraoccipital–parietal complex and several features of the squamosal, Machaeroprosopus lottorum n. sp. bridges the morphological gap between species previously referred to the genera Pseudopalatus and Redondasaurus. A parsimony analysis of known species of Machaeroprosopus supports the hypothesis that the development of the rostral crest in Machaeroprosopus is a sexually dimorphic feature, and questions the validity of the genus Redondasaurus. Consequently, Redondasaurus is here considered a junior synonym of Machaeroprosopus.