Field of Science

Skull Mechanics of Capitosaurs (Amphibia: Temnospondyli)

Fortuny, J., Marcé-Nogué, J., Gil, L. and Galobart, À. 2012. Skull Mechanics and the Evolutionary Patterns of the Otic Notch Closure in Capitosaurs (Amphibia: Temnospondyli). The Anatomical Record (advance online publication) doi: 10.1002/ar.22486 http://onlinelibrary.wiley.com/doi/10.1002/ar.22486/abstract

Abstract - Capitosaurs were among the largest amphibians that have ever lived. Their members displayed an amphibious lifestyle. We provide new information on functional morphology data, using finite element analysis (FEA) which has palaeoecological implications for the group. Our analyses included 17 taxa using (2D) plate models to test four loading cases (bilateral, unilateral and lateral bitings and skull raising system simulation). Our results demonstrates that, when feeding, capitosaurs concentrated the stress at the circumorbital region of the capitosaur skull and cranial sutures probably played a key role in dissipating and absorbing the stress generated during biting. Basal members (as Wetlugasaurus) were probably less specialized forms, while during Middle- and Late Triassic the group radiated into different ecomorphotypes with closed otic notch forms (as Cyclotosaurus) resulting in the strongest skulls during biting. Previous interpretations discussed a trend from an open to closed otic notch associated with lateral repositioning of the tabular horns, but the analysis of the skull-raising system reveals that taxa exhibiting posteriorly directed tabular horns display similar results during skull raising to those of closed otic notch taxa. Our results suggest that various constraints besides otic notch morphology, such as the elongation of the tabular horns, snout length, skull width and position, and size of the orbits affect the function of the skull. On the light of our results, capitosaur skull showed a trend to reduce the stresses and deformation during biting. Capitosaurs could be considered crocodilian analogues as they were top-level predators in fluvial and brackish Triassic ecosystems.

A New Neocalamites from the Upper Triassic of China

Zan, S.-Q., Axsmith, B. J, Escapa, I., Fraser, N. C., Liu, F.-X., and D.-E. Xing. 2012. A new Neocalamites (Sphenophyta) with prickles and attached cones from the Upper Triassic of China. Palaeoworld (accepted manuscript). http://dx.doi.org/10.1016/j.palwor.2012.04.001

Abstract - Remains of the extinct sphenophyte (horsetail) Neocalamites are most widespread in the Middle–Upper Triassic and are typically represented by stem and leaf fragments. Here we report on spectacular new finds of Neocalamites from the Late Triassic Yangcaogou Formation in Liaoning Province, China that include bedding surfaces dominated by nearly complete aerial stems with attached leaf whorls and rare bractless cones. They reveal a monopodial growth habit for the stems, which are covered with downward projecting prickles that probably provided protection against herbivores. These features provide the basis for a new proposed species, Neocalamites horridus. The nodes bear whorls of very long leaves mainly free to their bases, and one specimen bears an attached cone on a long peduncle. Identical dispersed cones have also been recovered. The leaves of adjacent monopodial stems most likely interlocked to support growth in large stands akin to the role now played by branches in large modern Equisetum species. The new Chinese Neocalamites is among the most confidently reconstructed species, and indicates a greater diversity of sphenophyte morphology during the Mesozoic than previously realized.

Introducing Protome batalaria, a New Phytosaur from the Chinle Formation of Petrified Forest National Park, Arizona

In the Fall of 2004 Michelle Stocker and I were out at the Battleship NW fossil locality in Petrified Forest National Park with several researchers from Northern Arizona University. They were working on completing the geological map of the area and had noted that they could not get the current stratigraphic scheme we were using (introduced in 2002) to work out on the map.  The stratigraphic position of this quarry was an important issue behind this work as I had just collected a good skeleton of the aetosaur Calyptosuchus wellesi here just above a prominent sandstone that previous workers had correlated to the "Sonsela Sandstone Bed". If this bed correlation was correct then the specimen would be from the Revueltian biozone. This was problematic because Calyptosuchus is considered an index taxon of the Adamanian.  As we hemmed and hawed back and forth and discussed various possible correlations to work out these problems, Michelle noted some scraps of bone in unconsolidated sand at top of this bed and very near to where we were standing. She was very surprised, as was I, when she reached down and pulled up part of the skull roof of a phytosaur.

After the NAU researchers moved on to complete their work, we examined Michelle's new "quarry" much closer.  By literally sifting our fingers through the loose sand we easily collected numerous parts of the skull including large portions of the rostrum and skull roof. We also uncovered a ramus of the mandible, but this was actually in-situ in the bedrock just underneath the loose sand. We were able to jacket this element, but it was wintertime and I distinctly remember how frozen our hands were after each application of a plaster bandage.  Luckily the truck was very nearby, so after each application we would run to the running truck to stick our hands under the heater.

Back in the lab we were able to piece back together much of the skull and it later became part of the focus of Michelle's Masters Thesis. Prior to this Randall Irmis and I mentioned (and figured) this specimen in a 2005 paper where we referred it to "Leptosuchus" adamanensis based on the overall morphology of the squamosals following work by Long and Murry. However, Michelle's detailed phylogenetic analysis in her thesis suggested something different, specifically the specimen did not form a clade with Smilosuchus adamanensis and instead was something else.

In her new paper in the Journal of Vertebrate Paleontology Michelle has described this specimen as a new taxon, which she names Protome batalaria. The name reflects the condition of the specimen, "face of an animal" and where it was found "warship" (for the Battleship Quarry). It can be diagnosed by a unique combination of characters as well as three autapomorphies of the braincase and lower jaw. Her phylogenetic analysis recovers it as a non-pseudopalatine leptosuchomorph.

Important discussion in her paper revolves around the importance of the use of apomorphies to describe and classify specimens. In this particular case past workers (myself) had focused on the generally morphology of the squamosal and robustness of the specimen to make a taxonomic assignment and ignored other discrete apomorphies of the material, which a phylogenetic analysis later determined to be of significance.  Thus the longtime practice of assigning isolated phytosaur squamosals to taxa based on general similarity and utilizing these for Late Triassic biochronology is called into question. This general squamosal morphology used to assign (fragmentary and complete) specimens to Rutiodon or Leptosuchus instead just appears to be a shared character of non-pseudopalatine leptosuchomorphs, a paraphyletic assemblage.

As recommended by Michelle it is now necessary to go back to collections such as those from the Petrified Forest and look carefully at all of the specimens assigned to "Leptosuchus" and sort them out using apomorphies. Hopefully this will provide a clear distribution pattern and biochronological signal for these specimens, testing their importance in phytosaur biochronology and biogeography.  Overall this new paper provides a great description and discussion that Michelle should be proud of and will be landmark (along with her 2010 paper) for sorting out the labyrinth that is phytosaur taxonomy.

By the way, the stratigraphic problem mentioned at the beginning of this post was finally figured out by Jeff Martz and I in 2009 when we discovered that the bed in question was definitely not the "Sonsela Sandstone Bed", but rather an isolated sandstone lens in the older Lot's Wife Beds and  Adamanian in age.

Stocker, M. R. 2012. A new phytosaur (Archosauriformes, Phytosauria) from the Lot’s Wife beds (Sonsela Member) within the Chinle Formation (Upper Triassic) of Petrified Forest National Park, Arizona. Journal of Vertebrate Paleontology 32(3): 573-586 DOI:10.1080/02724634.2012.649815

Abstract - A new phytosaur taxon from Petrified Forest National Park, Arizona, is here described based on cranial material from a single individual. This specimen previously was included in an extensive phylogenetic analysis, and it was found to possess a combination of character states that differs from all known phytosaur taxa in addition to two autapomorphies within the braincase and an autapomorphy of the mandible. The new taxon adds to the taxonomic diversity recognized from the Sonsela Member of the Chinle Formation. The continued increase in phytosaur diversity emphasizes the need to more accurately characterize and identify taxa within a phylogenetic systematic context in order to produce a more refined signal for biostratigraphic correlations, biochronologic inferences, and faunal dynamics during the Late Triassic.