Some were the size of a dog. Others were as large as polar bears. A newly-discovered fossil of the ferocious hyaenodont is helping scientists understand a little bit more about the mysterious ...

Read more: These 12 Prehistoric Sea Animals Are Pure Nightmare Fuel Tigers and lions are one thing, but there's just something about a big cat that has massive, knife-like, canine teeth to go with ...

Recently analyzed fossils finally confirm a longtime paleontological theory: Flying squirrels the size of domesticated cats glided across ... which lured prehistoric mammal species east after ...