Following up their 2000 discovery of an ancient reptile commonly referred to as SuperCroc,  paleontologists from the University of Chicago and McGill University today unveiled key fossils of five previously unknown or poorly understood crocodile species. Most of them walked "upright" with their arms and legs under the body like land mammals, with their bellies touching the ground. The discoveries are reported in the latest issue of ZooKeys.

The five new species, dubbed BoarCroc, RatCroc, DuckCroc, DogCroc and PancakeCroc by University of Chicago Paleontologist Paul Sereno, lived roughly 100 million years ago and ultimately survived the dinosaurs.

"We were surprised to find so many species from the same time in the same place," said paleontologist Hans Larsson, associate professor at McGill University in Montreal and a team member who discovered the bones of BoarCroc and PancakeCroc. "Each of the crocs apparently had different diets, different behaviors. It appears they had divided up the ecosystem, each species taking advantage of it in its own way."

(Photo by Mike Hettwer, courtesy National Geographic)
To better understand how these ancient crocs — mostly upright and agile — might have moved and lived, Sereno traveled to northern Australia, where he observed and captured freshwater crocs. Realizing while there that he may have stumbled onto one of the keys to crocodilian success, Sereno saw freshwater crocs galloping at full speed on land and then, at water's edge, diving in and swimming away like fish. On land they moved much like running mammals, yet in a flash turned fishlike, their bodies and tails moving side to side, propelling them in water.
Based on interpretation of the fossils, Sereno and Larsson hypothesize that these early crocs were small, upright gallopers. In the scientific paper, they suggest that the more agile of their new croc menagerie could not only gallop on land but also evolved a swimming tail for agility and speed in water, two modes of locomotion suggested to be evolutionary hallmarks for the past 200 million years.

(Photo by Mike Hettwer, courtesy National Geographic)

The researchers CT-scanned the skulls of DuckCroc and DogCroc and then created digital and physical casts of the brains to learn more about the creatures. The result: Both DogCroc and DuckCroc had broad, spade-shaped forebrains that look different from those of living crocs. "They may have had slightly more sophisticated brain function than living crocs," Larsson said, "because active hunting on land usually requires more brain power than merely waiting for prey to show up."

To collect the croc fossils, Sereno and his teams endured temperatures topping 125 degrees F, living for months on dehydrated food. Logistics were challenging: For the 2000 expedition, they transported trucks, tools, tents, five tons of plaster, 600 pounds of water and four months' worth of other supplies.

Citation: Paul C. Sereno, Hans C. E. Larsson, 'Cretaceous Crocodyliforms from the Sahara',
ZooKeys, 2009, doi: 10.3897/zookeys.28.325