Bunnies may look like fluffy eared rodents, but they are not. They have their own zoological order called Lagomorpha, which comprises hares, rabbits and a Guinea pig-like family of mammals called pikas.

Now, scientists have found what appears to be the oldest remains of an ancestor of today's rabbits and hares. The 53-million-year-old fossils are made of small ankle bones and they were uncovered in Gujarat (central India). The remains are described in the journal Proceedings of the Royal Society B: Biological Sciences.

The previous oldest lagomorph species had been encountered in Central Asia and it lived between 40 and 48 million years ago.
The latest discovery was made in clay beds in the Vastan lignite mine, north-east of Mumbai. These fossils come from the early Eocene Epoch, coinciding with the period when mammals first started to experience the evolutionary boom that led to the modern forms.

This research pushed the age of the lagomorphs far beyond 53 million years ago. The ankle bones encountered at Vastan clearly show some anatomical traits typical for hares and rabbits, thus the species was already advanced and lagomorphs were diversifying by the early Eocene.

The discovery also shows that an early evolution of the mammals took place in the moment when India was colliding with southern Asia. The Eocene explosion in the mammal evolution has been connected to an acute episode of global warming that occurred 55 million years ago.

The temperatures of the planet increased by 6 degrees C (11F) in less than a millenium, being one of the swiftest and extreme global warming events recorded on Earth. It was not completely explained, but the higher temperatures could have induced a rapid release of methane from the sea bed. This is a greenhouse effect gas much more powerful than carbon dioxide.