When you think of kangaroos, you usually imagine the six-foot-tall kind, hopping across wide open spaces throughout Australia ...

An artist’s impression of the newly described fossil species Protemnodon viator and its relative Protemnodon anak, compared at scale to the living red kangaroo and eastern grey kangaroo.

Kangaroos are pretty peculiar on the outside: They're the world's largest marsupials, they hop to get around, and they use their tails as a fifth limb. But they're also pretty unusual on the inside: ...