One day last spring, fossil hunter and Johns Hopkins
anatomy professor Kenneth Rose was
displaying the bones of a jack rabbit's foot as part of a
seminar at the
School of Medicine when
something about the shape of the bones looked oddly
familiar.
That unanticipated eureka moment — that those
bones resembled unidentified ones Rose and his
fossil-hunting team had found a few years ago in India
— has led researchers at the school to the
discovery of the oldest-known record of rabbits. The fossil
evidence, found in west-central India,
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.
In the study, published online in the February
Proceedings of the Royal Society, the
investigators say previous fossil and molecular data
suggested that rabbits and hares diverged about
35 million years ago from the pika, 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 Rose found that the
characteristics of their rabbit bones were very similar
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
rabbitlike features, according to Rose, a professor in the
Center for Functional Anatomy and Evolution
at the School of Medicine.
"What we have suggests that diversification among the
Lagomorpha group — all modern-day
hares, rabbits and pikas — may already have started
by the Early Eocene," he said.
Rose says the 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."
But sure enough, the tiny bones — about a
quarter of an inch long — from India turned out to
look remarkably similar to ankle and foot bones from
modern-day jack rabbits, which are four to five times
bigger.
Rose and his team set out and measured every dimension
of their Indian bones and compared
them to eight living species of rabbits and hares. They
also compared them to two species of the
related pika, that mouselike, mountain-dwelling critter
that lives in the Rocky Mountains of North
America, among other places.
Using a technique called character analysis, the team
first recorded measurements of 20
anatomical features of the bones, which showed that they
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 with 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.
Asked how many years of good luck one gets with a
53-million-year-old rabbit foot bone, Rose
quipped that he "already got lucky with the feet, but what
we really would like are some teeth that
tell how different these animals really were."
The research was funded by the National Geographic
Society; Department of Science and
Technology, government of India; Council for Scientific and
Industrial Research of India; Research
Foundation Flanders; and Belgian Federal Science Policy
Office.
Authors on the paper are Valerie Burke DeLeon and
Rose, both of Johns Hopkins; Pieter
Missiaen, University of Ghent, Belgium; R.S. Rana and
Lachham Singh, both of H.N.B. Garhwal
University in Uttaranchal, India; Ashok Sahni, Panjab
University, India; and Thierry Smith, Royal
Belgian Institute of Natural Sciences in Brussels.
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