YOUR LAST COMMON ANCESTOR

This fossil filled a gaping hole in scientists’ knowledge about a major stage in vertebrate evolutionary history

Is this lemur your great-to-the-nth grandparent? Or are you actually related to a sort of sponge at the bottom of a rock pool? Trick question!

For almost three decades, its bones had been forgotten in the basement of a Scottish museum. It had been categorised as a fish shortly after its discovery in 1971. That is, until British palaeontologist Jennifer Clack got hold of the fossil in 1996. She determined the creature, which was named Pederpes, was not a fish, but rather one of the first vertebrates to live on dry land. Before Clack’s exhaustive investigation of Pederpes, scientists lacked highquality fossils from this epoch. They knew about early animal fossils, which did not yet live on dry land, and later fossils of animals that were fully adapted to life on dry land, but had until then found nothing in between.

Pederpes’ primitive arms and legs gave scientist a long-awaited idea of the adaptations that made life on dry land possible. Pederpes’ aquatic ancestors had limbs that pointed down along their bodies and could not be used for very much other than swimming or pushing the animals away from the ocean floor. Pederpes’ limbs pointed away from the body, towards the ground, keeping the 1-m-long animal's body off the ground.

And Pederpes was not alone. Last year, Clack contributed to naming five new coexisting species, all showing similar forms of dray land adaptation.