Evrim Yazgin
Cosmos science journalist
How did mammal ancestors evolve from a sprawled posture like a lizard to the upright locomotion we see today? A new study sheds light on the puzzle.
The research, published in Science Advances, shows that the shift was a complex one that didn’t develop in a straight line.
Mammals diverged from reptiles about 325 million years ago.
A group of creatures called synapsids – sometimes called “mammal-like reptiles” or more correctly stem mammals or proto-mammals – dominated in the Permian period (299–252 million years ago) just before the dinosaurs emerged.
Mammals today also belong to the group synapsida.
In the shadow of dinosaurs, mammal ancestors remained small. Exactly when the first true mammals emerged remains a mystery.
Palaeontologists looked analysed bones of a variety of synapsid species which have lived over the past 300 million years.
Among them were fossilised remains of well-known Permian species such as the sail-backed Dimetrodon and wolf-like predator Lycaenops.
The research shows that the transition from sprawled to upright locomotion was intricate and occurred later than was previously believed. Some species showed flexibility in limb posture similar to that of a modern alligator.
Lead author Peter Bishop – a postdoctoral fellow at Harvard University and an honorary researcher at Australia’s Queensland Museum – says that Australia’s unique mammals help shed light on how mammal ancestors changed over time.
“Australia notoriously has a scant fossil record of the ancient ancestors of mammals, but among our modern mammalian fauna we have the most primitive species alive today – the echidna and platypus,” Bishop says.
“Studying these ‘living fossils’, as we did here, can provide unique perspective on understanding one of the most important behavioural transitions in our distant ancestors.”
