One out of every five mammal species alive right now is a bat—some

If the hothouse

when the upper and lower molars bit together, they could shear and grind at the same time.

mammals that find themselves washed up on islands are known to change aspects of their biology and behavior to adapt to the constraints of their new home. One of the most common

The development of grasslands,

There’s another clue that therapsids were raising their metabolisms and better controlling their body heat. Hair.

higher-latitude temperate regions were no longer separated from the tropics by deserts.

These were among the first mammals to develop high-crowned teeth, a godsend for eating tough vegetation, like dirt-encrusted roots and tubers. Because mammals can’t replace their teeth throughout their lives, eating hard foods is risky, as a broken tooth can mean a death sentence. Evolving supertall teeth, which can gradually wear down over many ye

tribes: the metatherians and eutherians. Metatherians include modern-day marsupials and their closest fossil relatives; eutherians encompass placentals—like us—and immediate kin.