The ancient origins of British mammals

By Melissa Marr  (2^nd Year PhD student) Between 26 000 to 21 000 years ago the earth was in the grip of an ice age and global ice sheets were at their maximum extent. Most of Britain was covered with glacial ice and the mammal species that existed were very different from today, consisting of species that had particular adaptations to cold environments. Temperate adapted mammals – those species that rely on warmer climates – were restricted to the Mediterranean peninsulas. As the ice sheets retreated and temperatures rose at the end of the last ice age these warm-adapted species began to emerge from their ‘refuges’ and recolonize Europe. My study focuses on a period starting around this time (c. 15 000 years ago) and covering a roughly 5000 year period which saw four marked and abrupt periods of warming and cooling. How did these rapid changes in climate affect mammal species re-entering Britain from Europe? This is the over-riding question of my PhD research. To answer this question I’m combining two techniques – ancient DNA and 3D geometric morphometrics. Mammals can respond to changes in their environment in three main ways; by adapting, by changing their range and/or by going locally extinct. These responses will leave a signature in the genetics and in the shape and size of the bones and teeth of ancient animals. Most of my time so far has been spent visiting museums and examining material excavated from caves and archaeological sites which has been a fantastic opportunity to meet curators and study the anatomy of long dead mammal species. To take samples for ancient DNA analysis I have to carefully drill within the bones of these fragile specimens and remove the powder. Back in the specially adapted sterile laboratory at the Natural History Museum, London I extract, amplify and sequence the DNA. By comparing the DNA sequences of these individuals I’m able to reconstruct the history of extinct populations.

Drilling a mid-late Holocene beaver cranium for ancient DNA at the Sedgwick Museum, Cambridge

I also spend a lot of time creating three-dimensional images of skulls, teeth and long bones. To do this I use a laser which creates a surface ‘map’ of the object and CT scanning which uses X-Rays to build up ‘slices’ of both the surface and interior of the object. By looking at the changes in shape of anatomical features in relation to climate I can make suggestions as to how the morphology of species was adapting to their changing environment.

Post-processing a 3D laser surface scan of an ancient beaver cranium

Around 8000 years ago the final collapse of the glacial ice sheets isolated Britain from the continent and ended mammal immigration back into Britain, giving us the native mammal communities that we have today. Determining how these communities developed in relation to climate change will allow us to gain insights into the impact climate has on the evolution of mammals over millennial timescales and, possibly, offer information that can help predict how climate change will impact our mammal fauna in the future.