Five ancient crocs, one with teeth like boar tusks and another with a snout like a duck's bill, have been discovered in the Sahara by National Geographic Explorer-in-Residence Paul Sereno and McGill Professor Hans Larsson. The five fossil crocs, three of them newly named species, are remains of a bizarre world of crocs that inhabited the southern land mass known as Gondwana some 100 million years ago.
Sereno, a professor at the University of Chicago, and his team members, including Larsson, unearthed the strange crocs in a series of expeditions beginning in 2000. "These species open a window on a croc world completely foreign to what was living on northern continents," Sereno said. These crocs, along with a closely related sixth species, are detailed in a paper published in the journal ZooKeys and appear in the current issue of National Geographic magazine.
At 40 feet in length and weighing 8 tons, Sarcosuchus imperator, or SuperCroc, was the first and largest of the crocs Sereno found in the Sahara, but it was not the strangest, Sereno said. He and his teams soon discovered key fossils of five previously unknown or poorly understood species, most of them walking "upright" with their arms and legs under the body like a land mammal instead of sprawled out to the sides, bellies touching the ground.
- BoarCroc: Kaprosuchus saharicus; fossils found in Niger. Twenty-foot-long upright meat eater with an armoured snout for ramming and three sets of dagger-shaped fangs for slicing. Closest relative found in Madagascar.
- RatCroc: Araripesuchus rattoides; fossils found in Morocco. Three-foot-long, upright plant and grub eater. Pair of buckteeth in lower jaw used to dig for food. Closest relative in South America.
- PancakeCroc: Laganosuchus thaumastos; fossils found in Niger and Morocco. Twenty-foot-long, squat fish eater with a three-foot pancake-flat head. Spike-shaped teeth on slender jaws. Likely rested motionless for hours, its jaws open and waiting for prey. Closest relative from Egypt. The scientific paper also names a close relative discovered by the team in Morocco, Laganosuchus maghrebensis.
- DuckCroc: Previously named species, Anatosuchus minor; fossils found in Niger. Three-foot-long upright fish-, frog- and grub-eater. Broad, overhanging snout and Pinocchio-like nose. Special sensory areas on the snout end allowed it to root around on the shore and in shallow water for prey. Closest relative in Madagascar.
- DogCroc: New fossils of named species, Araripesuchus wegeneri; fossils found in Niger include five skeletons, all next to each other on a single block of rock. Three-foot-long upright plant and grub eater with a soft, doglike nose pointing forward. Likely an agile galloper, but also a capable swimmer. Closest relative in Argentina.
"We were surprised to find so many species from the same time in the same place," said Larsson, who along with a team member discovered the bones of BoarCroc and PancakeCroc. "Each of the crocs apparently had different diets, different behaviours. It appears they had divided up the ecosystem, each species taking advantage of it in its own way."
Based on interpretation of the fossils, Sereno and Larsson hypothesize that these early crocs were small, upright gallopers. 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.
To study the crocs' brains, Sereno CT-scanned the skulls of DuckCroc and DogCroc and created digital and physical casts of the brains. 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 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.
For Prof. Hans Larsson
cynthia.lee [at] mcgill.ca
For Prof. Sereno
bmoffet [at] ngs.org
Colour illustrations - including reconstructions of the crocs' heads: Kate Baylor, kbaylor [at] ngs.org.
Professional video footage: bmoffet [at] ngs.org.
The scientific paper can be accessed at:
"When Crocs Ate Dinosaurs" airs Nov. 21 on NGC's second annual Expedition Week.