Crocodiles are beasts with an odd mix of features: they are ectothermic (meaning that they derive their body heat from their environment) reptiles, like lizards and snakes, but unlike those smaller critters, they have a fairly sophisticated, high performance cardiovascular system: they have a true four-chambered heart, just like us mammals and birds, and they also have a diaphragmaticus, a muscle analogous to our diaphragm that is used to inflate the lungs. At the same time, their hearts are relatively small—heart mass is roughly 0.15% of body mass, compared to 0.4%-0.7% of body mass for mammals—and generates relatively low systemic blood pressure.
It's weird. It's like they have this fancy, sophisticated engine in low-tech chassis, that the animal never revs up to its full potential. How did it get in there, and why do crocodiles have such fancy hearts?
The answer may be that they inherited it from more active, endothermic ancestors.
Continue reading "Hot-blooded crocodiles?" (on Pharyngula)