High Blood Flow Into the Femur Indicates Elevated Aerobic Capacity in Synapsids Since the Synapsida-Sauropsida Split

Varanids are the only non-avian sauropsids that known to approach warm-blooded mammals in stamina. Furthermore, a much higher maximum metabolic rate (MMR) gives endotherms (including birds) stamina than crocodiles, turtles, and non-varanid lepidosaurs. This has led researchers hypothesize mammalian endothermy evolved as second step after acquisition of elevated MMR non-mammalian therapsids from plesiomorphic state low rates. In recent amniotes, correlates with index blood flow into femur ( Q i ), which is calculated femoral length cross-sectional area nutrient foramen. Thus, may serve an indicator range extinct animals. Using proxy phylogenetic eigenvector maps, here we show MMRs near base Synapsida. Non-mammalian synapsids, including caseids, edaphosaurids, sphenacodontids, dicynodonts, gorgonopsids, cynodonts, values varanids, suggesting raised either synapsids shortly Synapsida-Sauropsida split Mississippian or lepidosaurs turtles apomorphic, been postulated for crocodiles.