Some of the earliest mammals had more specialised diets than previously thought, leading to key evolutionary traits we carry today.
Shrew-sized mammals living 200 million years ago in the Jurassic period were thought to be opportunistic insect-eaters with a generalised diet. But a new study by a team of researchers including the Museum's Nature Live science communicator Dr Nick Crumpton shows that two core taxa of early mammals had teeth and jaws adapted to specific kinds of insects.
At this time, small early mammals were known to be evolving the precise chewing and better hearing that are traits of mammals worldwide today. However, it was thought that, because of their general diets, these traits did not evolve in response to different hunting and feeding behaviours.
The new research shows teeth and jaws of early mammals were in fact becoming specialised as a response to different diets.
The Early Jurassic basal mammals, Morganucodon and Kuehneotherium, hunting their prey on the small island they shared in what is now Glamorgan, southern Wales. © John Sibbick.
Dr Crumpton said this gives us new ideas on how the earliest mammals lived:
The idea of the first mammals eking out a meagre living, hiding in the shadows whilst dinosaurs ruled the land is a pervasive one, but we have revealed that even the earliest mammals were already showing specialisations for certain lifestyles.
Tale of the teeth
The team, led by the Universities of Bristol and Leicester, analysed 2cm long jaws and tiny teeth from the mammals Morganucodon and Kuehneotherium found in Glamorgan, South Wales. When the creatures were alive 200 million years ago, the area was made up of small islands in a shallow sea.
Bits and pieces of jaw were scanned and the images stitched together to allow the researchers to determine the bite and strength of the creatures' jaws. This was combined with evidence of 'microwear' on the teeth, patterns of pits and scratches that indicate what the animal was eating.
The patterns on the ancient mammal teeth were compared to those of insect-eating bats alive today that have specialised diets. The combined evidence shows that Morganucodon favoured harder, crunchier food such as beetles, while Kuehneotherium prefered softer prey such as moths and scorpion flies.
Old specimens, new techniques
Dr Crumpton said this research also highlights the importance of specimens that may have been in the collections for decades, but still have stories to tell:
Although our methods were very modern, the fossils themselves had been stored in collections including the Natural History Museum for decades. It's work like this that shows how important museum collections are, and that even though those techniques didn't exist in the 1950s, we were able to study them in fresh new ways in order to discover the secrets they held.