Some 250 million years ago, a single warm-blooded ancestor gave rise to two of nature's most enduring lineages — one that became birds, soaring on the metabolic fire of endothermy, and one that became crocodiles, which quietly surrendered that fire altogether. New research reveals this was no passive inheritance but an active evolutionary reversal: crocodiles abandoned high metabolism roughly 66 million years ago, trading the demands of warm blood for the cold patience of an ambush predator. In doing so, they may have purchased their own survival through the very catastrophe that erased their