evolution ,

Was prehistoric crocodile a land lover?

MICHIGAN STATE (US)—The toothy grin of a recently discovered prehistoric reptile looks more mammal-like than that of modern crocodiles, according to an international group of researchers.

Molar-like teeth in the jaw of the house cat-size species, dubbed Pakasuchus kapilimai, resemble the complex teeth of mammals more than the simple pointed teeth found in modern crocodile jaws.

“What we’ve discovered is a small crocodile that looks better adapted for living on land than living in water,” says Michael Gottfried, associate professor of geological sciences at Michigan State University and curator of paleontology at the MSU Museum.

“It’s something that doesn’t fit the stereotypical view of what we think a crocodile does.”

Details of the discovery appear in Nature.

With mammal fossils from that prehistoric time and place as scarce as hens’ teeth, the croc might have helped fill the small mammal ecological niche while eating smaller invertebrates such as insects and, possibly, plants.

A distant, long-extinct cousin to modern crocodiles, Pakasuchus (Paka is the Ki-Swahili name for cat and souchos is Greek for crocodile) appears more thinly armored, except along its tail, and its limbs suggest it moved more nimbly on land. Its nasal openings also face forward rather than up, further suggesting a landward lifestyle.

At the time Pakasuchus lived, Africa was part of a larger southern supercontinent called Gondwana, where evolution in some groups seems to have proceeded differently than on northern continents.

The discovery team’s main specimen is a rare complete skeleton encased in sandstone, so CT-scan technology was used to explore the skull in detail.

It lived during the Cretaceous Period of the Mesozoic Era, between 80 million and 110 million years ago, in what geological evidence suggests was a dry landscape crisscrossed by a large river system.

The area supported a variety of life, including large plant- and meat-eating dinosaurs. The team has unearthed fish, turtle, and dinosaur bones in the same deposit, and a single lower jaw of a small, primitive mammal.

Gottfried says the team has much more work in front of it to fully explore the region. It lies in southwestern Tanzania’s Rukwa Rift Basin, which runs between two of Africa’s great lakes.

“We’ve done nine field seasons in this part of Tanzania, and we certainly don’t think we’ve found everything interesting that’s to be found there,” he says.

Seeking to understand what drove the evolution of southern hemisphere vertebrates, while their northern cousins were diversifying differently, the research team settled on their location after reading mid-20th-century geological survey reports describing fossilized bones and dinosaur eggshell found there.

Also contributing to the study were researchers from the University of Dar es Salaam in Tanzania, Ohio University, Stony Brook University, James Cook University, Northeastern Ohio Universities College of Medicine, the University of the Witwatersrand in South Africa, and the Tanzanian Antiquities Unit.

The project was supported the National Geographic Society, National Science Foundation, MSU, Ohio University, and the University of the Witwatersrand in South Africa.

More news from Michigan State University: http://news.msu.edu/

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