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Outlasting the Dinosaurs (continued)

NOVA: Can you speculate on what else might have helped them outlast the dinosaurs?

Photo of young American Caimans Ross: Well, there is their association with water. Whatever devastated the terrestrial environments 65 million years ago—and the strong suspicion now is that it was an asteroid impact causing a long-term climatic change through dust in the atmosphere—appears to have had a less intense impact on freshwater environments. You can speculate on why crocodiles may have been able to survive that. For one thing, you can look at how crocodiles are kept in commercial captivity. In the less favorable situations, they're kept in complete darkness, under the most appalling conditions of bad hygiene. People fail to clean the water and toss them stinky dead stuff for food. Yet they go on thriving in these conditions. A nuclear-winter, meteor-impact scenario would be similar. It would be dark all the time—that apparently doesn't bother alligators. Dead stuff would be falling in the water as the rest of the fauna succumbed to the collapse of the food chain. The crocodiles conceivably were big enough to survive through that and under conditions that most other organisms couldn't tolerate.

NOVA: And crocs can go for long periods without eating, right?

Ross: Yes, they have an awesome capacity to deal with starvation. There are numerous examples of animals not feeding for an entire year. They become desperately thin, but they're still active and are perfectly capable of feeding when food appears. So again, if the demise of the dinosaurs was caused by an asteroid-winter type of scenario, then crocodiles may well have been able to survive that.

Photo of American Crocodiles There is another element. Crocodiles, for all their ability to get their body temperature up when they have sunlight, do very well at low body temperature in the darkness. All their systems continue to work adequately well. There is some speculation that at least all the big dinosaurs were probably homoiothermic, or warm-blooded. That is, they had developed the circulatory and metabolic changes that enable one to maintain a body temperature independently of the surrounding temperature.

If this was so, they constantly had to pay the great cost of becoming warm-blooded, which as we know ourselves is you have to eat all the time. The energetic cost of maintaining your body temperature burns up more than 80 percent of what you eat. So dinosaurs that had made the commitment to becoming warm-blooded had given up their capacity to not eat for long periods. At the time that was a very effective trade-off, but when crunch time came with the asteroid or whatever it was, it was the crocodiles that still retained the primitive ability to continue to function at low body temperature and therefore not require as much to eat.

NOVA: Just how cold can they take it?

Ross: It depends a great deal on the species, but the three species that occur in temperate zones—the American alligator, the Chinese alligator and the broad-snouted caiman—can tolerate occasional frost or freezing. There are records of alligators surviving beneath ice as long as they can continue to breathe. Of course, alligators normally become quiescent in cold weather anyway. They dig deep burrows into the banks of rivers and lakes and retire to them. They don't hibernate in the strict sense, because they don't reduce their metabolism down close to zero. But they're able to tolerate low temperature quite well.

Continue: How long can they remain submerged?

Outlasting the Dinosaurs | Who's Who of Crocodilians
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