Wednesday, November 9, 2011

SVP 2011 Roundup - Triassic Crurotarsan/Pseudosuchian Edition

"A new archosaur (Diapsida: Archosauriformes) from the marine Triassic of China." Wu, X., Li, C., Zhao, L., Sato, T., and Wang, L.
  • a new, nearly complete (except for some of the tail) crurotarsan archosaur from the Falanf Formation (Middle Triassic - Ladinian) of China 
    • likely a basal poposauroid (sensu Nesbitt 2011), about 1.5 meters in length
  • snout more than twice the length of the rest of the skull (about 24 cm total)
  • although found in marine sediments, it has few anatomical modifications toward an aquatic lifestyle but still not likely fully terrestrial (fish gut contents, posteriorly positioned external naris)
  • sister-group relationship with Qianosuchus (only other Middle Triassic archosaur found in marine sediments of China), but with a poor bootstrap value
"An enigmatic archosauriform from the Manda Beds (Middle Triassic) of Southwestern Tanzania: character conflict at the base of Pseudosuchia." Nesbitt, S., Sidor, C., Angielczyk, K., Smith, R., and Tsuji, L.
  • a new archosaur with an unusual mix of character states
  • basal pseudosuchian, closely related to/ just outside of Paracrocodylomorpha
  • new data produces little change in relationships but a drastic change in character optimization (overall data is still obscured by high rates of homoplasy and incomplete specimens)
  • shows that the plesiomorphic bauplan of archosaurs was likely "rauisuchian"

"Comparative paleohistology of Triassic rauisuchian and aetosaurian osteoderms (Archosauria:Pseudosuchia)." Scheyer, T., Desojo, J., and Cerda, I.
  • sampled 8 rauisuchian, 10 aetosaurs, and Revueltosaurus
  • rauisuchians had compact bone, showed high growth rates early, and reduced growth rates later in development
  • in aetosaurs, a few taxa showed rapid growth, but most showed slow growth (parallel-fibered/ lamellar-zonal bone)
  • Revueltosaurus showed mostly densely remodeled parallel-fibered bone
"A newly recognized specimen of the phytosaur Redondasaurus from the Upper Triassic Owl Rock Member (Chinle Formation) and its biostratigraphic implications." Parker, W., Martz, J., and Dubiel, R.
  • a phytosaur specimen from the Owl Rock Member (Chinle Fm) has been identified as Redondasaurus, not Pseudopalatus
  • this puts mush of the Owl Rock in the Apachean Biozone, drastically changing biostratigraphic correlations of the upper Chinle and Dockum
  • shows that there is no basis for the Tr-5 unconformity (no faunal turnover or depositional hiatus)
"The relationships and type locality of Heptasuchus clarki, Chugwater Group (Middle to Upper Triassic), Southeastern Big Horn Mountains, Wyoming, USA." Zawiskie, J., Dawley, R., and Nesbitt, S.
  • type locality is poorly constrained, but likely equivalent to the Popo Agie Formation
  • Heptasuchus is the sister taxon to Batrachotomus
  • minimum of four Heptasuchus individuals at the type locality, further suggesting that loricatans may have lived in groups (like Decuriasuchus)
"The trackmaker of the Late Triassic tetrapod footprint ichnotaxon Brachyirotherium was an aetosaur." Lucas, S., Heckert, A., and Lockley, M.
  •  aetosaurs have the appropriate manus/pes morphology, were capable of a nearly over-stepped stride, and have the appropriate geographic/stratigraphic distribution to be consistent with Brachyirotherium
  • rauisuchians and spenosuchians excluded by manus/pes morphology
"Diversity of aetosaurs (Archosauria: Stagonolepidae) in the Upper Triassic Pekin Formation (Deep River Basin), North Carolina." Schneider, V., Heckert, A., and Fraser, N.
  •  new specimen of a partial aetosaur carapace, composed of the first ten rows of osteoderms (including a full, articulated row of cervicals)
  • shows character states of both Longasuchus and Lucasuchus
  • at least three genera of aetosaur in the Pekin Formation (Lucasuchus, Coahomasuchus, and whichever genus is represented by the new specimen), correlating it with the lower Dockum Group
"A virtual phytosaur (Archosauria: Crurotarsi) endocast and its implications for sensory system evolution in archosaurs." Holloway, W. and O'Keefe, R.
  • cranial endocast (CT scan) of a complete Smilosuchus adamanensis skull
  • endocranial morphology very similar to Crocodylus johnstoni except for enlarged pineal body in Smilosuchus
  • "This highly conserved cranial endocast morphology is consistent throughout Crurotarsi, regardless of overall body morphology or ecology, with a trend of pineal body size reduction from the enlarged basal condition to a reduced crown condition." (quoted from the abstract)

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