After six years of collaboration between over twenty scientists from research institutions across the country, researchers have completed the most comprehensive picture of mammalian ancestry to date. Using a combination of physical and genetic data, the researchers reconstructed the family tree of placental mammals–a group that now comprises over 5,100 species–and traced its many branches back to a common ancestor.
The tree’s huge wealth of anatomical data allowed the researchers to reconstruct what that common ancestor probably looked like:
It was mouse-size and grey-brown, with a furry tail. It ate insects. It gave live birth to naked, squirmy babies, and its descendants diversified to fill all the ecological vacancies left by the recently-departed dinosaurs. There were a lot of vacancies, and within just a few hundred thousand years–a blink of the evolutionary eye–the mammalian lineage branched into a wide array of creatures that, in time, would become the ancestors to every placental mammal–from whales to horses to bats to humans–living today.