The discovery of a beaver-like fossil which lived
when the dinosaurs ruled the planet was expected to challenge some
of the then-currently accepted ideas on mammal evolution.
Castorocauda lutrasimilis, which was
unearthed in China, was a species which was previously unknown to
science. It dated back to 164 million years ago, a time at which
mammals were thought to be primitive creatures confined to the land.
But this animal was adapted to life in water, meaning that scientists
faced the possibility of a rethink of their theories.
The fossil was found in the Middle Jurassic Jiulongshan
Formation, a deposit rich in the remains of dinosaurs, early insects,
and other organisms. The creature had fur, a broad scaly tail, and webbed
feet for swimming. It was about 42cm in length and had seal-like teeth for
eating fish. Castorocauda lutrasimilis resembled a modern-day beaver,
but belonged to a group that became extinct long before rodents
Such advanced features surprised many scientists at
the time of its discovery, suggesting that mammals which lived during
the heyday of the dinosaurs had already conquered a variety of
environments. The mammals of the time were once largely thought to be
primitive shrew-like creatures, scuttling around the feet of dinosaurs,
and only flourishing when the dinosaurs died out some 65 million
Commenting on the find, which was revealed in the
Science journal, Thomas Martin of the Forschungsinstitut Senckenberg
in Frankfurt, Germany, said it showed that mammals had conquered the
water 100 million years earlier than previously thought. This exciting
fossil was a further piece in the jigsaw puzzle, one of a series of
recent discoveries which served to demonstrate that the diversity and
early evolutionary history of mammals was much more complex than
was perceived less than a decade ago.