New Permian temnospondyls & warm-blooded crocs

[Tim Williams <twilliams_alpha@hotmail.com>]

Sidor, C.A., O'Keefe, F.R., Damiani, R., Steyer, J.S., Smith, R.M.H., 
Larrson, H.C.E., Sereno, P.C., Ide, O., and Maga, A. (2005).  Permian 
tetrapods from the Sahara show climate-controlled endemism in Pangaea.  
Nature 434: 886 - 889.

Abstract: New fossils from the Upper Permian Moradi Formation of northern 
Niger provide an insight into the faunas that inhabited low-latitude, xeric 
environments near the end of the Palaeozoic era (251 million years ago).  We 
describe here two new temnospondyl amphibians, the cochleosaurid _Nigerpeton 
ricqlesi_ gen. et sp. nov. and the stem edopoid _Saharastega moradiensis_ 
gen. et sp. nov., as relicts of Carboniferous lineages that diverged 40?90 
million years earlier.  Coupled with a scarcity of therapsids, the new finds 
suggest that faunas from the poorly sampled xeric belt that straddled the 
Equator during the Permian period differed markedly from well-sampled faunas 
that dominated tropical-to-temperate zones to the north and south.  Our 
results show that long-standing theories of Late Permian faunal homogeneity 
are probably oversimplified as the result of uneven latitudinal sampling.


Also:

Summers, A.P. (2005).  Evolution: Warm-hearted crocs.  Nature 434: 833-834.

Which cites this paper:

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.  Physiol. Biochem.  Zool. 77: 1051?1067.

Abstract: Physiological, anatomical, and developmental features of the 
crocodilian heart support the paleontological evidence that the ancestors of 
living crocodilians were active and endothermic, but the lineage reverted to 
ectothermy when it invaded the aquatic, ambush predator niche.  In 
endotherms, there is a functional nexus between high metabolic rates, high 
blood flow rates, and complete separation of high systemic blood pressure 
from low pulmonary blood pressure in a four-chambered heart.  Ectotherms 
generally lack all of these characteristics, but crocodilians retain a 
four-chambered heart.  However, crocodilians have a neurally controlled, 
pulmonary bypass shunt that is functional in diving.  Shunting occurs 
outside of the heart and involves the left aortic arch that originates from 
the right ventricle, the foramen of Panizza between the left and right 
aortic arches, and the cog-tooth valve at the base of the pulmonary artery.  
Developmental studies show that all of these uniquely crocodilian features 
are secondarily derived, indicating a shift from the complete separation of 
blood flow of endotherms to the controlled shunting of ectotherms.  We 
present other evidence for endothermy in stem archosaurs and suggest that 
some dinosaurs may have inherited the trait.