Crocodiles are the prototypical cold-blooded creature. Both figuratively and literally. According to new research published in Paleobiology and detailed by its authors in The Conversation, crocodiles became literally cold-blooded in an effort to become more figuratively cold-blooded.
Scientists had always assumed that crocodiles had always been relatively slow-paced reptiles. Meanwhile, some of their closest relatives, dinosaurs and birds, eventually figured out how to run. Somewhere along the way, crocs and birds got themselves a shared ancestor that was warm-blooded and had a high metabolism. Odd, considering the crocodile is the poster boy for cold-bloodedness.
The researchers found this out by studying the size of the tiny holes in the leg bones of 81 ancient archosaur species. The holes carried blood vessels, and larger vessels in animals generally indicate higher blood flow and metabolism. The fossil evidence suggests that animals in the crocodile lineage maintained high-energy lifestyles for most of their evolutionary history, until about 66 million years ago when the asteroid came along and effectively cut that line off.
How the Chicxulub Asteroid Shifted Crocodile Biology
That asteroid, the Chicxulub impact, wiped out global ecosystems and dinosaurs along with it. The crocodile, meanwhile, survived, and one of the things that helped it stick around in a world without as many food sources was by flipping from warm-blooded to cold-blooded so it could slow down its metabolism.
As far as life pivots go, this one worked out pretty well. Modern day crocodiles are ambush artisans, lying in wait just beneath the surface of the water to ensnare some unsuspecting prey and its powerful jaws. Being cold-blooded helps them conserve energy and remain underwater for longer.
Evidence of their past warm-bloodedness can be found in their four-chambered hearts, suggesting that they once skittered about much more quickly than they do today. Though modern day crocs have been known to hoof it now and then when they need to.
A fearsome killer croc that’s seemingly moving at a snail’s pace, without a care in the world, with seemingly no haste whatsoever, isn’t lazy; that’s tens of millions of years of evolution making sure that they remain as food-efficient as possible.
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