Mother's Day as a holiday is only 105 years old, but moms on the direct and extended human family tree date back to at least 58 million years ago.

That's when Plesiadapis, the oldest known primate-like mammal, lived. Infants were fully formed but helpless, so mothers must have provided a great deal of care. Resembling squirrel-like lemurs, Plesiadapis moms also spent a lot of time scurrying around the ground and in trees.