This story appears in the November 2009 issue of National Geographic magazine.
In the summer of 2008 an American crocodile left Florida's Biscayne Bay, swam along a yacht-lined canal through the upscale neighborhood of Coral Gables, and took up residence on the campus of the University of Miami, where it occasionally interrupted its sunbathing on the banks of Lake Osceola to munch on a turtle. The snaggletoothed croc was a daily reminder to students that they'd chosen a school in sunny, subtropical Florida and not in, say, Iowa.
This wasn't the first crocodile to appear on campus, but it became the most famous. People took to calling it Donna, after university president and former Cabinet member Donna Shalala—this despite the fact that it turned out to be a male. Donna occasionally basked on the grass just yards from the university pub, prompting the relocation of a few picnic tables but causing no further disruption.
Early on October 1 someone killed Donna, an act that outraged students and faculty and broke both state and federal laws: The American crocodile is classified as endangered by Florida law and threatened by federal law. A month after the crime, police arrested a man and a teenage boy, who allegedly wanted the skull as a trophy.
It's tempting to use Donna as a metaphor for the plight of the world's 23 recognized species of crocodilians, a group of related reptiles including crocodiles, alligators, caimans, and gharials. Having endured millions of years of planetary climate change, tectonic-plate musical chairs, and other ecological vicissitudes, they face a new challenge to their survival: us.
In the 1970s the population of crocodiles in Florida may have dropped to fewer than 400 individuals. The state's booming human population had crowded them out of most of the protected saltwater bays where they once lived, and many were killed by poachers for their hides, stuffed for museum displays, or captured for live exhibits.
In the years since, conservation measures have led to a rebound in Florida crocs, which may now number some 2,000. "Crocodile management isn't rocket science," says Steve Klett, manager of Florida's Crocodile Lake National Wildlife Refuge. "If you protect their habitat and protect them from being killed, they will respond. The big issue now is the restricted range: Once they've occupied all the available habitat, where will they go?"
In Donna's case, to an urban area where he shouldn't have been living—except that there was probably no better alternative.
Today's crocodilians are often said to be survivors from the age of dinosaurs. That's true as far as it goes: Modern crocs have been around for some 80 million years. But they're only a small sampling of the crocodilian relatives that once roamed the planet—and, in fact, once ruled it.
Crurotarsans (a term paleontologists use to include all croc relatives) appeared about 240 million years ago, generally at the same time as dinosaurs. During the Triassic period, crocodile ancestors radiated into a wide array of terrestrial forms, from slender, long-legged animals something like wolves to huge, fearsome predators at the top of the food chain. Some, like the animal called Effigia, walked at least part of the time on two legs and were probably herbivores. So dominant were crurotarsans on land that dinosaurs were limited in the ecological niches they could occupy, staying mostly small in size and uncommon in number.
At the end of the Triassic, about 200 million years ago, an unknown cataclysm wiped out most crurotarsans. With the land cleared of their competitors, dinosaurs took over. At the same time, huge swimming predators such as plesiosaurs had evolved in the ocean, leaving little room for interlopers. The crocs that survived took on a new diversity of forms, but eventually they lived, as their descendants do today, in the only places they could: rivers, swamps, and marshes.
Restricted ecological niches may have limited the creatures' evolutionary opportunities—but also may have saved them. Many croc species survived the massive K-T (Cretaceous-Tertiary) extinction 65 million years ago, when an asteroid dealt a death blow to the dinosaurs (except for birds, now viewed as latter-day dinosaurs) and a broad range of other life on land and in the oceans. No one knows why crocs lived when so much died, but their freshwater habitat is one explanation: Freshwater species generally did better during the K-T event than did marine animals, which lost extensive shallow habitat as sea level dropped. Their wide-ranging diet and cold-blooded ability to go long periods without food may have helped as well.
With land-based dinosaurs and sea monsters gone, why didn't crocs take over the Earth once and for all? By then mammals had begun their evolutionary march toward world domination. Over time the most divergent lines of crocs died out, leaving the squat-bodied, short-legged forms we're familiar with.
"The main change in recent crocodilian conservation has been the decline in illegal hunting for skins," says John Thorbjarnarson of the Wildlife Conservation Society, a leading expert on the group. It's been replaced by legally managed ranching and harvesting, allowing some species to rebound. "Whereas 20 years ago there may have been 15 or 20 species that were listed as endangered," Thorbjarnarson says, "now there are really only seven, all reflecting the loss of most of their habitat."
Species such as the Chinese alligator and the Philippine crocodile have virtually no natural habitat left, squeezed out of their former ranges by agricultural and urban growth. And even species that have responded positively to conservation measures face a problem that's a larger scale version of Donna's: contact, and often conflict, with humans.
The Indian gharial, a skinny-snouted species that once ranged from Pakistan to Myanmar, suffered serious population declines in the mid-20th century. Recovery in the 1980s and 1990s, thanks to decreased poaching and establishment of protected areas, gave conservationists reason to believe it was out of trouble. But recent surveys have shown that gharial numbers have once again crashed, this time to critically endangered status.
Gharials eat only fish and require a specialized habitat of swiftly flowing rivers with sandy banks. Factors in their decrease include persecution by fishermen (who see them as competitors), drowning in fishing nets, and destruction of their habitat by sand mining and other human activities. In addition, a significant gharial population on India's Chambal River was decimated between December 2007 and February 2008 by what some biologists believe was pollution. The wild population of gharials has shrunk to a few hundred individuals living only in India and Nepal.
Some crocodilians found in remote parts of the world are not in immediate danger, and others such as the American alligator have made dramatic recoveries. But it remains to be seen how many can endure in a world where their wetland homes are coveted by people from subsistence farmers to golf course designers—and where some species make themselves less than welcome by eating pets and even people.
Thought to be an origin of ancient dragon myths, crocodilians and their ancestors have faced nearly unimaginable changes to the planet and found ways to adapt to them all. As the pace of environmental change quickens, though, their greatest challenges are yet to come.