Fossil of crocodile with erect stance found

Jeff Poling

About 212 million years ago a small crocodile roamed the floodplain that is now the Connecticut River Valley. The crocodile had a fully erect stance like modern mammals, rather than the semi-sprawling stance of modern crocs or fully sprawling stance of modern lizards.

The 3-inch skull of the little crocodile turned up in exposed rock in a road cut. The discovery was made near Cheshire, Connecticut, in March 1995, but it took more than a year for scientists to classify the skull with any certainty and to remove the delicate bone from the hard matrix in which it was embedded. The find was announced during a news conference at Dinosaur State Park on Saturday, November 2, by the paleontologists studying the fossil: Dr. Paul Olsen of the Lamont-Doherty Earth Observatory of Columbia University, Dr. Hans-Dieter Sues of the Royal Ontario Museum in Toronto and Dr. Mark Norrell of the American Museum of Natural History.

Part of the interest in the skull stems from the rarity of vertebrate fossils of any kind from the Mesozoic era in the northeastern United States. Many tracks of dinosaurs and other animals of the Mesozoic have been found in Connecticut (particularly around Dinosaur State Park, south of Hartford), but fossils of the animals themselves have mostly disappeared, Dr. Olsen said.

The little crocodile discovered by Dr. Olsen, which has not yet been given a formal name, seems to be closely related to a similar Mesozoic crocodile with an erect stance, called Erpetosuchus, that was found in Scotland a century ago. Only one Erpetosuchus has ever been found, Dr. Sues said. While the Connecticut skull consists of actual bone, he said, the Scottish specimen, which was found in 1894 near Elgin, Scotland, is only an imprint of parts of the animal in soil that eventually solidified into coarse sandstone.

The croc, about 2 feet long, had long, graceful legs with four toes on the hind limbs and five toes on the forelimbs, and it had teeth only in the front of its jaws. The impression of the Scottish carcass shows that it also had armored skin plates. "We used to think that those plates were for defense,'' Dr. Sues said, "but it now looks as if they helped to support vertebrae assisting in the animal's upright stance.''

Although the Connecticut find consists only of a partial skull, its similarity to the Scottish specimen led to the conclusion that the animals were practically identical.

"This little reptile walked upright on its four legs, not with its legs splayed out, as is the case with modern crocodiles,'' Olsen said. "It could truly gallop, with all four feet sometimes off the ground simultaneously. We know that some present-day crocodiles in Australia can reach speeds of 15 miles an hour, so this Triassic-period crocodile could probably reach even higher speeds. It probably spent all or most of its time on land.''

By the time the galloping crocodiles appeared in the mid-Triassic period, small dinosaurs had evolved, but had not yet achieved the ecological dominance they reached in the later Jurassic and Cretaceous periods. Both lineages survived into modern times, with the crocodile lineage taking to the swamps and rivers and secondarily evolving a semi-sprawling stance, and the dinosaur lineage taking to the air.