Hot to Cold

Source The new view of the history of the crocodile lineage starts in the Triassic period, with them as active, land-dwelling, warm-blooded animals, in many cases even running on two legs. They diversified into hundreds of species over the Jurassic and Cretaceous periods, living on land, in salt and fresh water, and in between. However, they apparently remained warm-blooded until recently. Why did their metabolisms slow down? We think it may have been related to their current behavior as ambush predators in water. The low metabolic rates that come with being cold-blooded allow them to hold their breath longer to remain hidden while waiting for prey animals and while drowning them. There are no warm-blooded ambush predators in water alive today. Warm-blooded animals simply cannot hold their breath long enough. Reversion to a cold-blooded metabolism may have saved the crocodile lineage from extinction 66 million years ago, when an asteroid ended most dinosaur lineages, except, of…