The Indian fossils are about 53 million years old

The 53-million-year-old specimens consist of small ankle bones unearthed in Gujarat, central India.

They belong to early examples of an animal group called lagomorphs, which today comprises hares, rabbits and a hamster-like animal called a pika.

Details of the discovery appear in the journal Proceedings of the Royal Society B: Biological Sciences.

The oldest lagomorphs known before this were from Central Asia and date to between 40 and 48 million years ago.

The latest finds come from clay beds in the Vastan lignite mine, north-east of Mumbai in Gujarat.

They date to the early part of the Eocene Epoch, when mammals first began to diversify into their present day forms.

Early divergence

The study shows that the lagomorphs were already distinct from other mammals by 53 million years ago.

Analysis of some ankle bones from Vastan revealed anatomical features characteristic of hares and rabbits, suggesting that the lagomorphs were already beginning to diversify by the early Eocene.

The dates and locations of the finds suggests some of their early evolution must have taken place while India was in the process of colliding with Asia.

An explosion in the diversity of mammals has been linked to a sharp bout of global warming about 55 million years ago.

Global temperatures at the time rose by about 6C (11F) in less than 1,000 years - an event known as the "thermal maximum". It was one of the most rapid and extreme global warming events in the geological record.

The causes are not fully understood; but rising temperatures may have caused a sudden release from the sea floor of ice-trapped methane - a potent greenhouse gas - which contributed to greenhouse warming.