SVP 2011 Roundup - Archosauromorph Edition

Archosauromorphs and General Archosaur Evolution 

(in order of presentation)

Talks

"Archosauromorph bone histology reveals early evolution of elevated growth and metabolic rates." Werning, S., Irmis, R., Smith, N., Turner, A., and Padian, K.

•  extant and extinct ornithodirans show high metabolic rates, but not extant crocodylians
• study of evolution of growth rate in archosauromorphs through an expanded histological database and using much more rigorous methods for collecting data
• characters associated with high metabolic rates appear in a short, stepwise accumulation along the archosauriform tree
• a reversal likely occured along the pseudosuchian line
• Aetosaurs and relatives show early rapid growth, but slow growth later on
• Shuvosaurs show fast growth throughout life

"Postcranial skeletal pneumaticity and the evolution of archosaur respiratory systems." Barrett, P., Butler, R., Gower, D., and Abel, R.

• unidirectional airflow present in extant archosaurs
• soft tissue associated with unidirectional airflow/ postcranial skeletal pneumaticity (PSP) not preserved by fossil record but fossae, foramina, and laminae are preserved
• pseudosuchians (phytosaurs, aetosaurs, poposaurs) posses many vertebral laminae and fossae, but no internal features
• no conclusive evidence in extinct archosaurs other than saurischians and pterosaurs but still likely that they had less well-developed avian-like respiratory systems with non-invasive air sacs and unidirectional air flow

"Phylogenetic congruence between cranial and postcranial characters in archosaur systematics." Mounce, R. and Wills, M.

•  showed a significant incongruence of cranial and postcranial signals (cranial characters appear to be significantly less homoplastic)
• results may indicate different evolutionary rates between cranial and postcranial characters

"Osteohistology of Triassic archosauromorphs from the Karoo Basin of South Africa." Botha-Brink, J. and Smith, R.

• looked at Prolacerta, Proterosuchus, Erythrosuchus, and Euparkeria
• Early/Middle Triassic archosauromorphs (non-crown group) show fast growth early in their life
• early rapid growth and early onset of sexual maturity are consistent with the life history expected from harsh, unpredictable conditions after the Permian/Triassic extinction 

"New information on the Triassic vertebrate faunas of Antarctica." Sidor, C., Smith, R., Huttenlocker, A., Peecook, B., and Hammer, W.

•  small Prolacerta-like archosauromorph found under a Lystrosaurus and a Proterosuchus-like archosauriform
• vertebrates of the lower Fremouw Formation likely correspond to the post-extinction recovery fauna of South Africa (Karoo Basin)
• faunas of the two continents differentiate in the Middle Triassic
• using network science for faunal analysis

"Uniting microevolution and macroevolution in deep time: the zone of variability in Archosauromorpha." Bhullar, B., Bever, G., Merck, J., Lyson, T. and Gauthier, J.

•  a phylogenetic "zone of variability" (ZOV) occurs before apomorphies become fixed
• detected indirectly - stem members of a clade show lots of variability in character states before they become fixed in crown group members
• derived archosauriforms show an absence of a parietal foramen, an absence of supratemporals, and a complete lower temporal bar
• stem archosauriforms show a ZOV of these characters 
• detected directly - in a single taxon, variation in such character states occur between individuals
• in Prolacerta broomi, the three characters listed above in derived archosaurs are variably present and absent (in almost all permutations) in fossil individuals

Posters

"Anatomy and affinities of large archosauromorphs from the lower Fremouw Formation (Early Triassic) of Antarctica." Crandall, J., Hellert, S., Smith, N., Hammer, W., and Makovicky, P.

• first evidence of Archosauriformes in the Early Triassic of Antarctica
• found a partial presacral vert and distal end of the left humerus of a large archosauriform from just after the P/Tr
• large size is contra the "lilliput effect" of mass extinctions

"New data on the archosaur fauna of the Middle Triassic (Anisian) Ntawere Formation of Zambia." Peecook, B., Sidor, C., Nesbitt, S., Angielczyk, K., and Steyer, S.

• first diagnostic remains of archosaurs from the Ntawere Formation - teeth, large pseudosuchian vertebra, pelvic and vertebral material of a silesaurid
• Ntawere Formation (and Manda beds) shows a higher diversity of archosaurs than the ealier Karoo Basin