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Outlasting the Dinosaurs (continued) (back) 
NOVA: How long can crocs remain submerged, and how do
they manage it?
Ross: It's a tradeoff between what they're doing and how cold or warm it is. Maximum time seems to be on the order of an hour or two. When the temperature is fairly low and they're relatively inactive, they can remain beneath the surface for a prolonged period. I don't know of anybody who's really looked in detail at their diving physiology. But the general pattern of all organisms that have this capacity to hold their breath a long time is two-fold. One is they shunt blood away from non-vital tissue, and the anatomy of crocodiles suggests that they can do this. They have a very sophisticated circulatory system; it's one that doesn't really belong in a reptile. If you took the heart, lungs, and major veins and arteries of a crocodile, hung them up and asked ten physiologists what it was, most of them would say it was a mammal. Crocodilians have a well-developed four-chambered heart and the capacity to separate oxygenated blood and unoxygenated blood, which is quite unique among reptiles. 
NOVA: I've heard that crocodilians survive better from birth by orders of
magnitude over other reptiles.
Ross: They do remarkably well. The hatch rates of their eggs, when you compare them to other reptiles such as freshwater turtles and monitor lizards, are uniformly very high. Eighty or ninety percent of eggs laid hatch. Rates of predation on their nests, though they can be high, are lower than for other reptiles as well and generally are not catastrophic. NOVA: Crocs are said to use energy in food more efficiently than almost any other animal. Ross: Partially because they're cold blooded, they convert their food to crocodile tissue as well as or better than fish, which also are very efficient, and much, much better than chickens or cows or pigs or people. When food is available they can eat a lot of it, turn it into new crocodile and grow quickly. But then when food is not available, they appear to be able to shut down and live off their own tissue for a long period of time. 
NOVA: Do crocodilians feed cooperatively?
Ross: I have a photograph of mass feeding caiman, in which there are animals of quite different sizes all mixed in together at the mouth of a stream. The stream was flowing out into a larger river, and there are 40 or 50 of them all in a crescent array, apparently snapping up something that is washing out of the stream. This kind of behavior was first described by William Bartram back in the 1770s, during his trip through Florida, which he wrote up in his marvelous book "The Travels of William Bartram." He describes alligators at a narrow point in the St. John's River being thick enough that he could have walked from one shore to the other on their backs. This was once considered a truly fanciful account. People nodded and winked and wondered what young Bill was smoking out there in the Florida woods. Subsequently, we come to find that, particularly where there are schools of fish running through narrow channels, this sort of phenomenon has been described and even photographed in several species, including alligators. It looks like Bartram just happened upon one of these mass feeding events, during which there is a suspension of what might otherwise be aggressive behavior, a kind of mutual truce. 
You also see the opposite, of course. I have observed in the wild very clear
dominance relationships related to food sources. A dominant
animal will posture and display next to a source of
food—a dead animal say—and feed first on it. The others sit around
waiting. Only when the dominant one has had his fill and retired will the
others get what's left. There are no strict rules with crocodiles. Perhaps
their flexibility is part of their success.
Photos: Crocodile Specialist Group Outlasting the Dinosaurs | Who's Who of Crocodilians Wrestling with Crocs | The Clickable Croc | Teacher's Guide | Resources | Transcript Editor's Picks | Previous Sites | Join Us/E-mail | TV/Web Schedule | About NOVA Watch NOVAs online | Teachers | Site Map | Shop | Search | To Print PBS Online | NOVA Online | WGBH © | Updated December 2003 |