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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.
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.