For this, scientists use something called an "outgroup", a living descendant that still shares many of the ancestor's primitive traits. So we need a living jawless fish, like a lamprey.

Researchers have identified the first known prehistoric human from Taiwan which may represent an entirely new species that lived as recently as 10,000 years ago. The newly discovered big-toothed ...

The earless monitor’s slender body, reduced limbs, and lack of external ears reflect its adaptations to a semi-aquatic lifestyle, possibly primitive design that has survived through the ages.