Most Reptile Hearts Are Not Simple
Most living reptiles have two atria and one ventricle that is partly divided by muscular structures. This arrangement can direct blood along different pathways and can limit mixing under many conditions. Calling every non-crocodilian reptile heart simply three-chambered is accurate in outline but misses the internal anatomy of turtles, lizards and snakes.
Crocodilians Have a Distinct Design
Crocodilians have two atria and two ventricles, like birds and mammals, but they also retain two aortae and a connection between them called the foramen of Panizza. This anatomy permits controlled shunting in particular physiological situations, including diving. A four-chambered heart does not make crocodilian circulation identical to that of a mammal.
Structure Supports Different Lifestyles
Circulation must respond to temperature, activity, digestion and oxygen availability. Aquatic diving reptiles face different short-term demands from an active lizard in the sun, and each lineage has its own anatomy. Studying those differences helps explain function without assigning one group a more advanced place on an evolutionary ladder. Reptile circulation is diverse because reptile life histories are diverse.
