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endothermy in stem Archosauria



Thanks to HP Dunkelberg for pointing out to me that in the pages of
_Physiological and Biochemical Zoology_ there is a discussion of
evidence for endothermy at the stem of Archosauria:

Seymour, R.S., Bennett-Stamper, C.L., Johnston, S.D., Carrier, D.R.,
     and Grigg, G.C. (2004). "Evidence for Endothermic Ancestors of
     Crocodiles at the Stem of Archosaur Evolution", Physiological and
     Biochemical Zoology 77(6):1051-1067.  

Hillenius, W.J., Ruben J.A. (2004). "Getting Warmer, Getting Colder:
     Reconstructing Crocodylomorph Physiology", Physiological and
     Biochemical Zoology 77(6):1068-72.

Seymour, R.S. (2004). "Reply to Hillenius and Ruben", Physiological and
     Biochemical Zoology 77(6):1073-1075.

Seymour et al. argue based on several lines of evidence, primarily the
development and inferred evolution of the crocodilian heart, that
crocodilians are secondarily ectothermic.  Hillenius and Ruben argue
uh-uh!, and Seymour argues, uh-huh!.  Read the complete papers for a
more thorough discussion.

Seymour et al. argue that the reversion to ectothermy occurred after
the avian/crocodilian split.  I haven't read the articles carefully
(despite what you might have thought from my summaries above), but it
seems they're a bit vague about exactly when the transition back to
ectothermy occurred.  They do seem to think it was during the
Jurassic, however, and that most dinosaurs retained endothermy from
their earlier ancestors.  Some sauropods, hadrosaurs and other animals
large enough to take advantage of inertial homeothermy are considered
to have paralleled the crocodilian reversion to ectothermic
metabolism.

-- 
Mickey Rowe     (rowe@psych.ucsb.edu)