February 22, 2008
Fossils Found of Earliest Rabbit Relative
The oldest fossils to date of early rabbit relatives were recently unearthed. These specimens, which are 53 million years old, are tiny ankle bones which are clearly adapted to running.
These fossils belong to lagomorphs, a group which currently includes rabbits, hares and pikas. Prior to this finding which is published in the journal Proceedings of the Royal Society B: Biological Sciences, the oldest known lagomorphs dated to around 48 million years ago.
The ankle bones which were found in clay beds in Gujarat, central India, make an important evolutionary suggestion: rabbit-like creatures have existed in their distinct form in Asia for at least 53 million years, which is much longer than previously thought, and that some portion of their evolution took place in India. The location and age of these fossils suggest that they are from the time period during which India and Asia collided.
These fossils date back to an important period, the early part of the Eocene Epoch, which is when mammals began to diversify into their present forms. The anatomical features of these ankle bones suggest this early diversification, much earlier than previously assumed.
The specialization of mammals may be linked to an extreme stint of global warming nearly 55 million years ago. Over a period of less than 1,000 years global temperatures rose by 11 degrees Fahrenheit. This bout, known as the "thermal maximum", may have caused the release of ice-trapped methane gas from the sea floor, which then contributed to greenhouse warming.
Photo Caption: Calcanei of Eocene lagomorphs in (a-d) dorsal and (e-h) lateral views. Garhwal University, Srinagar, India (GU), and Institute of Vertebrate Palaeontology and Palaeoanthropology, Beijing, China (IVPP). (a,e) Left calcaneus, GU/RSR/VAS 711 from Early Eocene Vastan mine, India; (b-d, f-h) right calcanei from Middle Eocene of Shanghuang, China, IVPP 15537, 15538, 15539, respectively. ff, fibular facet; sf, sustentacular facet; PCF, posterior calcaneal facet; cf, cuboid facet, cc, calcaneal canal.
On the Net:
Proceedings of the Royal Society B: Biological Sciences
The full article can be viewed at http://journals.royalsociety.org/content/k7l678180886j05g/fulltext.html