View Full Version : The Complexity of Crocodilians

October 29th, 2004, 03:00 PM
October 26, 2004

Not Just Another Pretty Face


The adult alligator has 80 teeth and a tail that can dislocate a person's jaw with a single whack. "They get a bad rap for being stupid little reptiles," says a scientist who studies — and admires — them.

WASHINGTON, Oct. 25 - To the casual observer, an adult alligator afloat in an algae-dappled pond, its six-foot body motionless save for the sporadic darting of its devilish amber eyes, might conjure up any number of images, none of them fuzzy-wuzzy. A souvenir dinosaur. A log with teeth. A handbag waiting to happen.

For Dr. Daphne Soares, however, a neuroscientist at the University of Maryland, an alligator looks like nothing so much as a big, amphibious and grievously misunderstood kitten. Sure, it sports thick scales and bulging bony knobs called osteoderms rather than fur, and 80 teeth to the house cat's 30, and a tail that, as Dr. Soares learned from personal experience, can dislocate your jaw with a single whack.

But just look at the chubby belly, the splayed legs, the sunny smile that never sets! "Oh, you are so cute, so adorable, I wish I could just pick you up and give you a hug!" Dr. Soares cooed to the alligators that obligingly posed for her at the National Zoo here on a recent weekday afternoon.

Dr. Soares, 32, who was raised in Rio de Janeiro by a Brazilian mother and an American father and who conveys a blend of high energy and droll ease, has worked with many species of Crocodylia, the reptilian order that includes crocodiles, alligators, caimans and gharials. And while she admires the entire crocodilian dynasty, alligators are her favorite. "I absolutely love these creatures," she said. "They're beautiful, elegant and goofy at the same time."

They are also unmistakably observant, and as curious as, well, kittens. When Dr. Soares took a seat near the glass of the enclosure, the alligators paddled over for a close-up view. "They get a bad rap for being stupid little reptiles," she said. "But they're very curious, very alert, and they want to know what's going on."

In fact, the reptiles are virtual newshounds, for whom the term "current events" holds particular meaning. Dr. Soares, who specializes in neuroethology - the neural underpinnings of animal behavior - has lately discovered a kind of sixth sense unique to crocodilians, which are often referred to generically as crocodiles.

She has determined that the mysterious little bumps found around the jaws of some crocodile species and across the entire bodies of others, which naturalists had long observed but never before understood, are sensory organs exquisitely suited to the demands of a semisubmerged ambush predator.

The pigmented nodules encase bundles of nerve fibers that respond to the slightest disturbance in surface water and thus allow a crocodile to detect the signature of a potential meal - an approaching fish, a bathing heron, a luckless fawn enjoying its last lick of water.

The discovery of a novel sensory system is just one of a host of new findings about the prowess and performance of an impressively ancient and resilient clan. Crocodilians have toughed it out in one guise or another for 230 million years, some by land, others by sea, most astraddle, but all the while, stylishly crocodile.

"Our primate ancestors were ratty little things that went around stealing eggs," said Dr. Perran Ross, a crocodile specialist and professor of wildlife ecology and conservation at the University of Florida. "Ancestral crocodiles had basically the same body plan we see today, apparently because it works."

As scientists are just beginning to appreciate, that body plan is panzer, a tropical tank from the skin in. Beneath its scaly sheath and craggy osteoderms is another layer of armor, built of rows of bony overlapping shingles, or osteoscutes, that are both strong and flexible. And beneath that formidable barrier is an immune system that merits the modifier: it is virtually immune to defeat.

A crocodile wallows in mudholes, lagoons and other microbial Club Meds, yet it can suffer the most harrowing sort of injury - a limb torn off, its belly ripped open, its lower jaw sheared away - without so much as shedding a crocodile tear.

"Crocodiles have tremendous robustness against bacterial infection," Dr. Ross said. "The sort of wound that would leave any of us severely septicemic doesn't seem to touch them." That immunological ferocity has inspired researchers at the Johns Hopkins to begin screening crocodile blood in search of new antibiotics.

Crocodilians are also think tanks, and will engage in sophisticated behavior that leaves most reptiles in the cold. They vocalize to each other. They squabble over status and can distinguish between friendly hominid and annoying graduate student with dart gun. In caring for their young, they outcluck a mother hen, for what hen can protect her babies by carrying them in her jaw?

"They're not like big lizards," said Dr. George Amato, a geneticist at the Wildlife Conservation Society, a division of the Bronx Zoo. "It's clear when you spend time with them that they are quite complex."

They're not always like one another, either. Dr. Amato and his colleagues, including Dr. John Thorbjarnarson of the conservation society, are close to declaring that the so-called Nile crocodile, the giant meat eater renowned throughout Africa for having the might and maw to prey on adult zebras, wildebeest and the occasional fisherman, may not be a single breed of crocodile after all, as has long been thought, but rather two distinct species, one in East Africa and Madagascar, the other adding zest to the rivers and watering holes of Central and West Africa.

The two populations look roughly the same - the same shade of dug-up artichoke, the same heavy but pointy snout that distinguishes it from the blunter, rounder muzzle of an alligator, the same jutting bottom teeth that can still be seen when the jaws are shut, again in contrast to alligators. Yet the DNA sequences of the two crocodile factions are so distinct, said Dr. Amato, "they may not even be each other's closest relative."

Given the fact that there are only about two dozen crocodilian species in the world today, the designation of a new family herald would be considered a major event in the annals of crocodilian research, and would probably take years to gain general acceptance and appropriate nomenclature.

The researchers also would like to know which of the two crocodiles is the "true" Nile crocodile, that is, the crocodile so-named by the ancient Egyptians, who worshiped the reptile, modeled their river god Sobek after it, and on occasion mummified specimens with all the thanatoptic reverence normally reserved for pharaohs or - wouldn't you know it-the pharaoh's favorite cat.

Dr. Thorbjarnarson and Dr. Amato hope to obtain DNA samples from a mummified crocodile and compare them with those of the living varietals of the Nile.

Beyond rummaging through the past, conservationists are struggling to salvage some sort of future for the more critically endangered crocodilians. Not long ago, nearly all members of the order were under siege, shot as rank vermin or skinned like swank ermine, their swampy homes drained to make way for pastures and pavement.

But in the last 30 years, through the enactment of wetlands protection laws, bans on hunting and international trafficking in endangered animals and other measures, some species have recovered: visitors to the Florida Everglades soon grow blasé at the sight of American alligators, while in many rivers and parks of Latin America practically every rock is topped by a basking spectacled caiman, a gargoyle's glower stapled on its face.

Despite the success stories, about a third of all crocodilian species remain severely threatened, with several approaching oblivion. Among the imperiled are the Orinoco crocodile of Venezuela and Colombia, the Cuban crocodile, the Philippine crocodile, and the gharial of the Indian subcontinent, the most aquatic of all the crocodilians as well as the Most Likely to Succeed Pinocchio, its outrageously elongated snout specifically designed for catching fish.

More endangered still is the Chinese alligator, a compact and relatively mild-mannered meat eater that, at an average length of seven feet, is only about half the size of its American counterpart. The alligators once abounded by the hundreds of thousands, if not millions, through the lower Yangtze River basin in southeastern China. But over 5,000 years of rice cultivation, much of their terrain has been destroyed, and today, only 100 or so survive in the wild.

Working with environmental groups in China, Dr. Thorbjarnarson and his colleagues have begun reintroducing captive-bred alligators back into several choice sites. Last year they released three young adults into a dammed-up stream, where a tiny but well-established population of three to five alligators already lived. The newcomers apparently settled in without a fuss, and this September, the researchers were heartened to find that one of the liberated females had reproduced - though whether the father was a fellow releasee or a native of the pond they have yet to determine.

Rearing alligators in captivity is the easy part, scientists say. Much harder is finding suitable habitats in which freed animals can flourish. In China, that means persuading rice farmers to accept the presence of alligators all around. One way to encourage local cooperation, Dr. Thorbjarnarson suggests, might be through an appeal to cultural pride: in all likelihood, the Chinese alligator was the model for the Chinese dragon, an ancient symbol of good fortune.

Crocodiles also hark back to another cast of beloved goliaths, the real ones called dinosaurs. The resemblance is not circumstantial. Through recent taxonomic analysis, scientists have concluded that dinosaurs, crocodiles and birds should be classified together on one branch of the great polylimbed Sequoia of Life.

"Crocodiles really are the closest things we have to living dinosaurs," said Dr. Thorbjarnarson. They are also much more like birds than they are like snakes, iguanas or other reptiles. For example, whereas most snakes and lizards have hearts with only three chambers, and a consequent mixing of oxygen-rich and oxygen-depleted blood supplies, crocodiles and birds have a similarly elaborate cardiac layout, in which four chambers and valves keep oxygenated and unoxygenated blood flows separate. (Mammals independently evolved a four-chambered heart.) That capacity lends the animals significant metabolic flexibility and improves the performance of their brains.

Researchers have recently been astonished to observe just how birdbrained crocodilians can be in their behaviors. "Like birds, crocodiles build good nests, brood their eggs, protect their eggs, fuss over their eggs," Dr. Ross said. If the eggs get dry, mother drizzles them with urine. When the hatchlings emerge, they cheep like chicks, which alerts the mother to uncover the nest and begin carrying the newborns to the water. The mother may stay with her young for a couple of years, protecting them from predators and shepherding them through hard times.

Studying crocodiles during the dry season in Venezuela, Dr. Thorbjarnarson watched females lead their young to scarce sources of water by vocalizing back and forth. "The mother knew where the ponds were," he said, "and the only way the young could survive in dry conditions is to have the mother lead them from pond to pond."

For their part, male crocodiles are as territorial and status-conscious as are male birds, and they establish hierarchies that allow them to live in often crowded conditions without needing to risk their lives repeatedly in battle. "Crocodiles know their neighborhoods for miles around, and they know who's who, who's inferior, who's superior," Dr. Ross said.

Their aversion to potentially lethal acts of showmanship, coupled with the many hours they spend in the crocodilian zen of vigilant stillness, allows them to live for half a century or longer. Crocodiles don't like to make waves, though when they're hungry, they sure like to feel them.

Dr. Daphne Soares, with an alligator embryo, discovered a crocodilian sensory organ.

Sources: Florida Museum of Natural History; University of Michigan Museum of Zoology

Copyright 2004 The New York Times Company