palate of the small sparassodont from Bolivia
May 9, 2014

New Extinct Kitten-Sized Predator Identified After Decades On Display

redOrbit Staff & Wire Reports - Your Universe Online

Researchers at Case Western Reserve University have discovered an extinct, kitten-sized species believed to have lived in Bolivia some 13 million years ago, according to research appearing in the Journal of Vertebrate Paleontology.

According to third-year undergraduate student and evolutionary biology major Russell Engelman, the currently unnamed animal (UF 27881) would have been “about the size of a marten, a catlike weasel found in the Northeastern United States and Canada, and probably filled the same ecological niche.”

UF 27881 was a predator and one of the smallest species ever discovered in the extinct order Sparassodonta, a collection of carnivorous metatherian mammals that were native to South America. Engelman and anatomy professor Darin Croft discovered the creature by discovering a partial skull which had been on display for more than three decades at the University of Florida.

Engelman and Croft have chosen not to name the creature because the specimen does not possess well-preserved teeth, which are the only parts that have been preserved in many of the creature’s closest relatives. The skull, were it complete, would have been slightly under three inches long, and the animal would have had a short snout.

An alveolus (socket) in the upper jaw suggests that UF 27881 had large canines that were round in cross-section, such as those found in the spotted-tailed quoll (a modern-day carnivorous marsupial found in Australia), the study authors explained. The new Sparassodonta species likely dined on the ancient relatives of guinea pigs and spiny rats, and according to Croft, its biological features “indicate this small predator was a formidable hunter.”

After the partial skull was discovered, it had been provisionally identified as belonging to a specific group of extinct meat-eating opossums, the researchers said. This was due in part to its small size, and in part because the skull lacks teeth and the lower jaws – the fossils by which nearly all previous small sparassodonts have been identified.

Croft said that he wanted to study the skull because it is nearly twice as old as those belonging to the oldest previously identified species of carnivorous opossum, which was found in Bolivia in 1978 and found to be between 12 and 13 million years old. Both types of creatures have structurally similar skulls due to their shared diets.

“No single feature found in the skull was so distinctive that we could say one way or the other what it was, but the combination of features is unique and says this is a sparassodont,” he said. The fact that the orbital bone does not touch the nasal bone in the new species, as it does in the opossum, helped the authors make the distinction.

In their paper, Engelman and Croft wrote that the specimen “does not clearly correspond to any major sparassodont group… and represents a morphotype previously unknown among the Sparassodonta. UF 27881 is distinguished from other sparassodonts by its short, broad, borhyaenid-like rostrum and small size, among other features.”

“This specimen suggests that the appearance of the Sparassocynidae and several hypercarnivorous didelphid taxa… represent an evolutionary response to the decline in small, predatory sparassodont taxa during the late Cenozoic,” they added. “This study documents new morphological diversity among the Sparassodonta and highlights the value of fossils from traditionally undersampled parts of South America."

Image 2 (below): This shows skulls of several species of sparassodonts, including three large short-snouted forms (left), two smaller fox-like species (middle), and a reconstruction of the specimen described in the paper (far right). The site where this specimen was found can be seen in the background. Credit: Illustrations by Russell Engelman and photo by Darin Croft