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The crocodylians are a great example. There are monotremes that barely qualify as endothermic. I think McGrew is making it overly complicated. Looking at sea turtles, dinosaurs, birds, etc. endothermy did not arise once, but many times. If conditions favored it, loosing the ability to be homeothermic could save a lot of energy for a species. Ideas of it ...


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Secondary ectothermy has been suggested in living crocodylians by Seymour et al. (2004). Their rationale is based on: Presence of a 4 chambered heart (otherwise only found in endotherms) Post-cardiac shunting via the foramen of Panizza and "cog-tooth" valve, which develop secondarily in crocodylians Lung structure and ventilation during locomotion Thus ...


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There is no evolutionary "ratchet" that prevents a life form from evolving "backwards". However, it is statistically unlikely because it would pretty much require all of the environmental factors that changed during the transition from "cold blooded" to "warm-blooded" to change back in the reverse order, because all of those factors contributed to the ...


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