August 4, 2010

Scientists Unearth Ancient Mammal-Like Crocodile

Scientists reported in this week's issue of the journal Nature that they have discovered fossils of an ancient crocodile with mammal-like teeth in the Rukwa Rift Basin of Tanzania.

The scientists said the new species of notosuchian crocodyliform is a small, cat-sized animal that was not as heavily armored as other crocodiles, except along the tail. 

"If you only looked at the teeth, you wouldn't think this was a crocodile. You would wonder what kind of strange mammal or mammal-like reptile it is," said study lead author Patrick O'Connor, associate professor of anatomy in the Ohio University College of Osteopathic Medicine.

The molar teeth of the newly dubbed "Pakasuchus Kapilimai" possessed shearing edges for processing food, similar in form to the teeth of some mammalian carnivores.

"Once we were able to get a close look at the teeth, we knew we had something new and very exciting," O'Connor said.

The scientists found that the animal had heavily plated tails but relatively unarmored bodies with gracile limbs, which suggest the creatures were quite mobile.  They actively foraged on land, unlike water-dwelling crocodiles.

O'Connor said the new species is not a close relative of modern crocodiles, but is a member of a very successful side branch of crocodyliform lineage that lived during the Mesozoic Era.

"The more exploration we do, the more we push the boundaries on what we thought we knew about animal life on the planet," O'Connor noted.

The Pakasuchus lived alongside large, plant-eating sauropod and predatory theropod dinosaurs, other types of crocodiles, turtles and various kinds of fishes.

"We suspect that notosuchians were very successful in the southern hemisphere because they were exploiting a certain ecological niche, one in which they were able to successfully compete with other small-bodied, terrestrial animals," O'Connor said. "This is an environment that was quite different from what we typically think of for crocodiles."

The researchers are developing models of potential jaw movements and tooth-tooth interactions in a range of notosuchians.


Image 1: A photograph of the postcranial skeleton of Pakasuchus kapilimai as it appears partially prepared out of the red sandstone matrix. The researchers used a sandbox and foam padding (in blue) to position the separate fragments of the fossil prior to photographing the specimen. Credit: Patrick M. O'Connor, Ohio University

Image 2: The new species, Pakasuchus, isn't a close relative of modern crocodilians, pictured here, but is a member of a very successful side branch of the crocodyliform lineage that lived during the Mesozoic Era. Credit: Nancy Stevens, Ohio University


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