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Outlasting the Dinosaurs
An Interview with Dr. James Perran Ross

Crocodiles are the ultimate survivors. Having arisen some 200 million years ago, they have outlived the dinosaurs by some 65 million years. Even people, the most fearsome predators ever to stalk the Earth, have failed to force into extinction any of the 23 species of crocodilians (see Who's Who of Crocodilians). What makes them such consummate survivors? NOVA asked Dr. James Perran Ross, a croc researcher at the Florida Museum of Natural History and coordinator of the Crocodile Specialist Group, an international body devoted to conserving crocodilians of all stripes.

NOVA: Why did crocodilians survive when the dinosaurs went extinct?

Ross: The short answer is we don't know. But we can look at what crocodiles do now and how they work and speculate on some things that may be involved. Crocodile design has lasted an awfully long time. A great many of the fossils of crocodiles are virtually identical to the crocodiles we see today. They seem to have successfully adapted to their environment and have undergone few changes. That's not universally true, because crocodiles have occasionally veered off into some other quite interesting evolutionary lines. There is, for instance, a secondary return to terrestrial life among crocodiles. There's even a crocodile that had hooves, and one speculates it must have been a crocodile behaving like a small deer or something.

NOVA: I've heard of a fossil croc in Australia that was a tree-climber.

Ross: Conceivable. So they've periodically left the mainstream, but all those little branches didn't go anywhere. I think we have to look at their basic design and concede that it's a good way of being an amphibious predator. It really works. I think one of the aspects that may play to their survival is that they are extremely tough and robust. We're learning now that the immune systems of crocodiles, for instance, are just incredible. They can sustain the most frightful injuries.

NOVA: Such as?

Photo of Caiman

Ross: In territorial fights they commonly tear each other's legs off. They go away and sulk for awhile and seem to heal up. You often find animals in the wild with missing limbs, missing tails—what must have been very serious injuries. I found one in the wild with the whole of its lower jaw torn off, all healed up and swimming around. It was a bit skinny but had obviously survived that very traumatic event. So I think their inherent toughness is one aspect. They are also long-lived. They routinely live for decades.

The adaptability of their behavior is also something that may play into their survival. It certainly has in modern times. We haven't lost a species of crocodile to extinction since humans have been dominant on the planet, even in the last few hundred years when our impact has been appalling. The reason appears to be in large part because crocodiles learn quickly and adapt to changes in their situation. They particularly learn to avoid dangerous situations very quickly. For research purposes, we find that we often have to change capture techniques, because it's very hard to catch them with the same trick twice.

NOVA: Would you call that intelligence?

Photo of American Alligator

Ross: Well, it's certainly rapid learning. Whether they sit and ponder or whether they just have neural synapses that fire quickly is a moot point. There are some people who keep crocodiles who claim that they are truly intelligent. I know some people whose opinions I respect who very sincerely believe that crocodiles know individual people and that they learn simple routines very readily, such as when the man with the bucket has food and when he doesn't.

They also become tame quite readily. There are alligator shows all over the country in which people routinely handle quite large alligators, which have become used to being handled and take it in their stride. There are a couple of well documented stories of truly tame crocodiles. The famous crocodile biologist Frederico Medem described a doctor who lived in Villavicencio, Colombia who had a large Crocodylus intermedius, the Orinoco crocodile. He had raised it from a hatchling. It was a female about 10 feet long, and it lived in his house. It played with his children, it played with the family dog. Villavicencio is up in the hills, and this crocodile liked to come into the house and lie in front of the fire on cool winter evenings. And it was housetrained.

NOVA: Never knew crocs could be so sociable.

Photo of Chinese Alligator

Ross: They look a bit like logs, and everybody assumes they behave like logs. But studies have shown crocodilians to have quite complex social behavior. Individuals know other individuals and have long-term relationships with one another in terms of dominance and so forth. These relationships structure crocodile groups, certainly in captivity and probably also in the wild, in order to distribute access to food and even successful reproduction.

Of course, there's been some speculation that the dinosaurs also were more complex than we originally thought, in terms of things like maternal care. So again, I can't find any clear difference between what we know crocodiles do and what we suspect dinosaurs might have done, which is why it's hard to answer the question, Why did crocs survive?

Continue: Outlasting the dinosaurs.

Outlasting the Dinosaurs | Who's Who of Crocodilians
Wrestling with Crocs | The Clickable Croc | Teacher's Guide | Resources | Transcript