The Rise and Reign of the Mammals: A New History, from the Shadow of the Dinosaurs to Us

They ensure that even our coldest, driest breaths on the most frigid of winter days are warmed and humidified to rain-forest-like conditions within a split second. They also work in reverse, recouping precious water as we breathe out.

GIVEN THE GREAT diversity

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

“mammalian” attributes evolved piecemeal, over 100 million years of evolution, as coal swamp pelycosaurs gave rise to therapsids, therapsids survived the end-Permian extinction as small cynodonts, and cynodonts shrank further during the Triassic.

The dirt and phytoliths function as sandpaper, filing down the teeth of grazing mammals as they eat.

Archaeothyris—meaning “ancient window”—to highlight the most important feature of this animal: its large, portholelike opening behind its eye, which housed larger and more powerful jaw-closing muscles than its ancestors.

entirely new ecosystem had been invented,

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.