Crocodiles can't fly. Birds can. Scientists have finally figured out why

Crocodiles and birds share a common ancestry, both belonging to the archosauriform group that originated around 250 million years ago. As time passed, the lineage split, with crocodiles evolving as Pseudosuchia and birds as part of Avemetatarsalia. Despite this, crocodiles are cold-blooded (ectotherms) with low metabolic rates, while birds are warm-blooded (endotherms) with high metabolic rates allowing them to fly and sustain strenuous activity.

Scientists have traditionally believed that warm-blooded traits evolved from cold-blooded ancestors, but recent research suggests the opposite. The study analyzed fossil leg bone vascular openings in 81 archosaur species, revealing that early crocodile relatives, like their dinosaur-bird relatives, had high metabolic rates consistent with endothermy throughout most of their evolutionary history. This indicates that crocodiles, too, were warm-blooded at some point.

The researchers propose that crocodiles likely evolved to be cold-blooded relatively recently, possibly as an adaptation to their current behavior as aquatic ambush predators. Cold-bloodedness allows them to hold their breath longer while waiting for prey or drowning them, a strategy that may have helped them survive the mass extinction event 66 million years ago that wiped out most dinosaur lineages, leaving only birds as a surviving branch.