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Ancient crocodiles filled different, often scary niches

Paleontologists unveil fossils of five African species known as BoarCroc, RatCroc, DuckCroc, DogCroc and PancakeCroc. Some could gallop and eat dinosaurs.

November 21, 2009|By William Mullen

Crocodiles have a nasty reputation, but the leathery, snappish critters have been around so long that they probably gave dinosaurs a fright too.

On Thursday, University of Chicago paleontologist Paul Sereno and his colleague at McGill University in Montreal, Hans Larsson, unveiled fossils of five ancient crocodile species -- nicknamed BoarCroc, RatCroc, DuckCroc, DogCroc and PancakeCroc -- that lived with and, in some cases, hunted and ate dinosaurs that roamed what is now Africa's Sahara.

The first four, while spending time in water, also were very adept land animals that could get all four legs under their bodies and extend them to their full length -- unusual by today's croc standards. That allowed them to stand tall and gallop, chasing prey or escaping their own predators.

PancakeCroc, 20 feet long, got its name because of a bizarre, 3-foot-long, pancake-flat head and snout.

Sereno, in an interview Wednesday, said that this crocodile patiently held its jaws open underwater for hours to catch an unwary fish or frog. Like modern crocs, PancakeCroc -- formally named Laganosuchus thaumastos -- waddled on short legs extending from its side and never strayed from its riverbank home.

"The most basic story these five fossils tell us is that in the time of dinosaurs, crocodiles filled in a lot of ecologic niches later to be filled by small mammals," Sereno said.

"We're discovering a menagerie of fossil crocodiles in Africa, and they did a lot of things that crocodiles don't do today," he said.

BoarCroc, RatCroc and PancakeCroc are three new species introduced in a paper by Sereno and Larsson, published Thursday in the research journal ZooKeys. They also describe new fossil specimens of DogCroc and DuckCroc, both already known in scientific literature.

The animals lived in Africa when it was part of a single giant land mass called Gondwana, made up of the present-day southern continents and India.

Many bizarre fossil crocodiles have been found in South America, but Sereno's work is showing that Africa was equally rich in unusual crocodilian species.

In 2001, Sereno introduced the biggest known crocodile, SuperCroc (Sarcosuchus imperator), a 110-million-year-old fossil of a 40-foot, 8-ton killer that he discovered in Niger.

This paper offers "a pretty different, fairly exciting view of crocodiles," said Peter Makovicky, chairman of Chicago's Field Museum geology department and a dinosaur specialist, who had no role in Sereno and Larsson's research.

"Until now, the only place you saw diversity like this in crocodiles was in the Mesozoic [a geologic era 245 to 65 million years ago] in Madagascar and South America. It's pretty interesting to see some of these animals spending a lot their time on land, some of them eating plants," Makovicky said.

RatCroc (Araripesuchus rattoides), DuckCroc (Anatosuchus minor) and DogCroc (Araripesuchus wegeneri) were much smaller creatures, each about 3 feet long, all able runners that spent a lot of time out of the water, each using its own odd physiological adaptations to forage for food.

DogCroc, found in Niger, ran on long legs like a dog, but had a long crocodilian tail that also made it a very good swimmer. Sereno said that it probably ate more like a badger, dining on plants and animals, using its soft snout to push through foliage in search of food.

RatCroc, found in Morocco, had buckteeth that it used to root in soil for plants and grubs. DuckCroc, found in Niger, had a duckbill-like snout with a pointy nose to help it find fish, frogs and grubs to eat.

The much larger, 20-foot-long BoarCroc (Kaprosuchus saharicus), found in Niger, apparently was a swift runner and a ferocious carnivore that chased down smaller dinosaurs. It had three sets of huge upper and lower boar-like tusks on each side of its jaws that could slice through its prey's flesh like scissors.

"This thing is designed for power," Sereno said of BoarCroc. "He is a dinosaur-eater, with interacting canines designed to catch and kill something stronger than a fish."

DogCroc, DuckCroc and SuperCroc lived in the same time and place in Niger with several other croc species, Sereno said. SuperCroc was a nonrunner that probably spent its time in rivers, grabbing dinosaurs that waded in for a drink,

"Each of the crocs apparently had different diets, different behaviors," Larsson said. "It appears they divided up the ecosystem, each species taking advantage of it in its own way."

Crocodiles first appeared on Earth around the same time as dinosaurs, about 240 million years ago, and their fossils are found on every continent, including Antarctica. The ones Sereno and Larsson have found in Africa were in rock formations ranging in age from 95 to 110 million years old, in the Cretaceous period.

There are 23 species of living crocodiles. Only one of them, a croc Australians call "freshies" because they live around freshwater, is capable of lifting itself high on its legs and dashing like the fossil beasts in Africa that Sereno and Larsson have found.

The new crocodile discoveries, funded by the National Geographic Society, are featured in the November National Geographic Magazine. A documentary, "When Crocs Ate Dinosaurs," airs tonight on the National Geograpic cable channel.

wmullen@tribune.com

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