Ancient tiny teeth reveal first mammals lived more like reptiles

Reconstruction of Morganucodon (left) and Kuehneotherium (right) hunting in Early Jurassic Wales 200 million years ago. Original painting by John Sibbick, 2013. Copyright: Pam Gill Synchrotron micro-CT scan of a fossil Morganucodon tooth root from 200 million years ago. Elis Newham Scientists count fossilised growth rings in teeth like tree rings to find out how long the earliest mammals lived. Graphics: Nuria Melisa Morales Garcia. Morganucodon based on Bob Nicholls/ Palaeocreations 2018 model 12 October 2020 Pioneering analysis of 200 million-year-old teeth belonging to the earliest mammals suggests they functioned like their cold-blooded counterparts - reptiles, leading less active but much longer lives. The research, led by the University of Bristol, UK and University of Helsinki, Finland, published today , is the first time palaeontologists have been able to study the physiologies of early fossil mammals directly, and turns on its head what was previously believed about our earliest ancestors.