The newfound, cat-size crocodile Pakasuchus kapilimai (illustrated) had mammal-like teeth that helped give the fossil crocodile a power previously unknown among reptiles: the ability to chew.
One key to that ability is that the 105-million-year-old crocodile's lower jaw could slide back and forth (inset).
"Crocodiles alive today don't have a major sliding component to their jaw," said lead study author Patrick O'Connor, an Ohio University paleontologist. "It's just a hinged joint that allows the jaw to move up and down."
Illustration courtesy Zina Deretsky, National Science Foundation
"Cat Crocodile" Skull
Still permeated with the Tanzanian sandstone from which it was freed by archaeologists, the fossil skull of the newfound crocodile species (pictured in profile) measures about three inches (seven centimeters) long. (Video: Mammal-like Croc Found.)
Modern crocodiles have fairly undifferentiated, conical teeth specialized for a bite-and-gulp feeding style.
But Pakasuchus—literally, "cat crocodile"—had teeth resembling mammals' canines, premolars, and interlocking molars, says a new study, to be published in tomorrow's issue of the journal Nature.
Photograph courtesy John Sattler, Ohio University College of Osteopathic Medicine
Modern crocodiles—such as this Nile crocodile (file photo)—have nostrils positioned on the tops of their heads, for breathing while swimming. But Pakasuchus's nose was at the tip of its snout, canine style, according to the study.
"It was not like the crocodiles we know today, which are submerged much of the time. It was up, moving around on the land," said paleontologist Patrick O'Connor, who received a National Geographic Society/Waitt Grant for this project. (The Society owns National Geographic News.)
Photograph by Beverly Joubert, National Geographic
Partially liberated from Tanzanian sandstone, the Pakasuchus skeleton, minus skull, shows the fossil animal's unusually flexible spine.
This bendable backbone helps set the newfound crocodile species apart from modern crocodiles, as does Pakasuchus's lack of bony plates along its back—adaptations that may have helped the cat-size reptile leap at dragonflies and other flying fare, the study authors speculate.
Photograph courtesy Patrick M. O'Connor, Ohio University
Biodiversity in Black-and-White
Pakasuchus's flexible backbone (shown in an illustration of the new fossil, minus skull) adds to evidence that crocodiles alive during the time of the dinosaurs were much more diverse than previously thought, the study authors say.
Increasingly, fossil discoveries in former areas of Gondwana—the southern supercontinent on which Pakasuchus lived—are revealing that the notosuchian order of crocodiles, to which Pakasuchus belonged, boasted a very diverse range of species, said Steve Salisbury, a paleontologist at the University of Queensland in Australia, who did not participate in the Pakasuchus-fossil research.
Illustration courtesy Haley O'Brien, Ohio University
Study leader Patrick O'Connor (atop branch) and colleagues excavate a dinosaur limb bone from the Tanzanian sandstone cliff in which Pakasuchus's fossils were found.
During the Cretaceous period (100 to 65 million years ago), Tanzania and the rest of Africa formed part of the southern supercontinent Gondwana.
Lacking in many Cretaceous mammal fossils, Gondwana was rich in reptiles. With it's unique dentition, Pakasuchus may have filled ecological roles that would have otherwise been assumed by mammals, the researchers speculate.
Photograph courtesy Eric Roberts, James Cook University
Making full use of its lanky legs and bendy back, a Pakasuchus crocodile springs for dinner some 105 million years ago in an artist's conception. Pakasuchus likely fed on small lizards, insects, and the few primitive mammals that existed in Gondwana at the time.
"This small-bodied animal occupied a dramatically different feeding niche than do modern crocodilians" study co-author Nancy Stevens, also of Ohio University, said in a statement. The crocodilian order includes crocodiles, alligators, caimans, gavials, and related extinct forms.
Steve Salisbury, of the University of Queensland, said the discovery of Pakasuchus will likely prompt many scientists to go back and reexamine their fossil collections.
"Isolated teeth that people previously assumed belonged to mammals," he said, "may in fact belong to crocodiles."
Illustration courtesy Mark Witton, University of Portsmouth