How many chambers does a crocodile heart have

Crocodiles are ectothermic. A crocodile warms its body by laying in the sun. The blood under the skin in the tissues on the dorsal surface is warmed by the sun, but the blood deeper in the body and on the ventral side is not. As the warm blood and cool blood flows to and through the heart it mixes. This blood then needs to be pumped back to the body to cool the skin and warm the insides. Because the crocodile is resting, there is no need to pump most of this blood through the lungs.

That would be a waste of energy. Other reptiles achieve this same ability by having a single incompletely divided ventricle. Based on their lungs and heart, crocodiles seem like animals that evolved from endotherm ancestors. Financial Times. Washington Post. We support teachers How it Works. Online Resources. We investigate science education. Donate Our Work We support teachers. We block threats to science education.

In the Press. DIYSci Activities. October 24, Crocodilian hearts Summary of problems: We gain insight into heart evolution by looking across multiple animal groups. The crocodile heart demonstrates that evolutionary processes are not linear with distinct steps from 2 to 3 to 4 chambers , but are branching processes, which produces a range of final results from a common ancestral condition. This is exactly the evolutionary prediction.

Explore Evolution confuses matters by claiming this transition was difficult, reinforcing a common misconception about evolution. Crocodiles independently evolved a 4-chambered heart, demonstrating how easy that transition was, not as Explore Evolution claims how difficult it was. Jensen et al. The experiments provided unequivocal evidence of an atrioventricular node in crocodilians.

Among extant reptiles, crocodilians are the closest living sister group to birds. However, despite their four-chambered hearts and an atrioventricular node, all living crocodilians are clearly ectothermic and have low heart rates like other reptiles Hillman and Hedrick, ; Lillywhite et al. With their ability to walk with their body off the ground, their peculiar respiratory muscles, their avian-like lungs and various other traits, crocodilians may have once been endothermic Seymour et al.

According to this hypothesis, they switched to ectothermy when they adopted an entirely aquatic life style and became sit-and-wait predators with intermittent meals separated by long fasting periods. However, if past crocodilians had warm blood and some of the associated heart structures, have extant species lost their His and Purkinje fibers?

Would these cells — which support high-speed electrical signals — pose functional problems in animals with very low heart rates? The fact that crocodilians have an atrioventricular node also sheds light on the evolution of the vertebrate heart.

For example, the mere presence of a node and a division between the ventricles may be enough to prevent the electrical signal from 're-entering' the atria which would disrupt the operation of the heart.

These findings may also suggest that a nodal structure allows better fine-tuning of the heart rate by the autonomic nervous system. The next step is to characterize the electrophysiological properties of the cells in the atrioventricular node of crocodilians. Electrocardiogram recordings would also help to understand the exact timing of cardiac events, while flow and pressure measurements would capture the dynamics of the blood flow.

There may still be delightful discoveries awaiting us inside the four chambers of the crocodilian heart. This article is distributed under the terms of the Creative Commons Attribution License , which permits unrestricted use and redistribution provided that the original author and source are credited.

Article citation count generated by polling the highest count across the following sources: Crossref , PubMed Central , Scopus. Mammals and birds have a specialized cardiac atrioventricular conduction system enabling rapid activation of both ventricles.

This X ray shows a bone in the stomach of an alligator. Blood returning from the body to the heart has extra carbon dioxide. Carbon dioxide is also a building block of stomach acid, which helps digest food.

So, when blood rich with carbon dioxide goes to the stomach instead of the lungs, it can aid digestion. By Carolyn Gramling October 19, at pm.