The Paleocene transitions to the Eocene by a steep rise in global temperatures that lasted about 130,000 years. This is known as The Paleocene-Eocene THERMAL MAXIMUM. Average temperatures rose an estimated 9-18 degrees F. before cooling back down. As usual on Planet Earth, the lineages of mammals alive at the beginning of the temperature rise became miniaturized over the course of the thermal maximum. They regained larger size after the thermal period ended.

HORSE, CAMEL, AND DOG families arise in North America.

ELEPHANT, RHINO, AND PRIMATE families arise in the Old World.

LATE EOCENE (mini) EXTINCTION. Many types of large mammals disappear, including all the uintatheres and brontotheres and indricotheres. Primates, once abundant and diverse in North America, disappear from this continent. Rodent-like multituberculates, which had originated in the Cretaceous, go globally extinct. Asteroid impacts are implicated, as two large, buried craters (each half the size of the Yucatan crater tied to the dinosaur extinction) were discovered in the 1990s beneath Chesapeake Bay in the eastern United States and in Russia. They are dated to about 35 mya.w

Timeline of Eocene Era