Washington, March 20 : The discovery of a 53 million-year-old rabbit's bones in west-central India has been hailed by scientists as the oldest known rabbit.
The fossil evidence in hand, predates the oldest previously known rabbits by several million years and extends the record of the whole category of the animal on the Indian subcontinent by 35 million years.
According to the investigators, previous fossil and molecular data suggested that rabbits and hares diverged about 35 million years ago from pikas, a mousy looking member of the family Ochotonidae in the order of lagomorphs, which also includes all of the family Leporidae encompassing rabbits and hares.
But the team led by Johns Hopkins's Rose, who found the rabbit bones in India, said that they were very similar in characteristics to previously unreported Chinese rabbit fossils that date to the Middle Eocene epoch, about 48 million years ago.
The Indian fossils, dating from about 53 million years ago, appear to show advanced rabbit-like features, according to Rose.
"What we have suggests that diversification among the Lagamorpha group-all modern day hares, rabbits and pikas-may already have started by the Early Eocene," said Rose.
According to Rose, the new discovery was delayed a few years because the researchers had not been looking specifically to determine the age of rabbits.
"We found these bones on a dig in India a few years ago and didn't know what animal they came from, so we held onto them and figured we'd look at them later," he said. "It didn't occur to us they would be rabbits because there were no known rabbits that early in time and the only known rabbits from that part of the world are from central Asia," he added.
But one day, while using the jackrabbit foot bones as a teaching tool for a class, the shape of the bones in the class struck him as something he'd seen before among his collection of unidentified bones.
Sure enough, the tiny bones about a quarter of an inch long from India looked remarkably similar to ankle and foot bones from modern day jackrabbits, which are 4 to 5 times bigger.
Using a technique called character analysis, the team first recorded measurements of 20 anatomical features of the bones, which showed that the bones are definitely Lagomorph and closer to rabbits than pikas.
The scientists then ran a series of statistical tests on the individual measurements to see how they compared with the Chinese fossils as well as living rabbits and pikas.
They found that although the Indian fossils resemble pikas in some primitive features, they look more like rabbits in specialized bone features.