Nicholas Bakalar for National Geographic News September 19, 2006
A new species of ancient mammal has been discovered—in the fossil collection of the National Museum of Natural History in La Paz, Bolivia.
The animal, which has been assigned the tongue-twisting name Hemihegetotherium trilobus, is a member of an extinct group called notoungulates, a term that means "southern hoofed mammals."
The creature resembles a cross between a dog and a hare. It was about the size of a beagle, weighing between 20 and 25 pounds (9 and 11 kilograms), and probably looked something like a capybara, the largest modern-day rodent.
Specimens of the creature's bones—including almost complete skulls and jaws and parts of the skeleton—have been in collections in various museums for more than 30 years.
"Normally, you think of finding these in the field," said Darin A. Croft, an assistant professor of anatomy at the Case Western Reserve University School of Medicine in Cleveland, Ohio.
"But for this animal, no one who specialized on this group had taken a close look. No one had had the time or the expertise to look at the detailed anatomy."
Croft found the bones in a sample drawer while visiting the museum during a 1999 paleontology conference in Bolivia.
He noticed at the time that the molars had three lobes, whereas other notoungulates' teeth had only two, so he decided to study the remains further.
Croft and colleagues describe their findings in the June issue of the Journal of Vertebrate Paleontology.