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New Permian temnospondyls & warm-blooded crocs




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.