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

their amniotic eggs, with membranes to nourish, protect, and keep their embryos moist. They moved freely across the land, establishing connections between regions that were previously isolated, and in doing so, evolving new species, new body types, larger size, new diets, new behaviors.

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

Warm-blooded animals—technically called endotherms—have broken free of this handicap. They produce their own heat—often by packing more energy-producing mitochondria into their cells—and

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

two key features of mammals. The olfactory bulbs—which orchestrate the sense of smell—are massive. And the top of the cerebrum boasts a new structure: a six-layered mass of nervous tissue called the neocortex,

none of these mammal ear bones were new inventions. They were jaw bones that evolution repurposed for a new function: hearing.

Their greater leaf vein densities (which could transport more water) and increased number of stomata

The head was repositioned to sit atop the neck instead of sticking out in front of it.

Putting this evidence together, mothers must have started nursing early in mammal history, probably right around the time the first mammals like Morganucodon were scuttling around in the Triassic, and definitely by the time docodonts were flourishing in the Jurassic. It is probably no coincidence that enlarged brains appeared right around the same