Modern mammal orders appear at the boundary
Horses, deer relatives and true primates show up abruptly in the northern hemisphere, all at once.
- When
- —
- Duration
- 200 thousand years
- Known to
- ± 100 thousand years
- Era
- Eocene, Cenozoic
Immediately at the PETM the northern fossil record changes character. The first true primates, the first even-toed ungulates and the first odd-toed ungulates all appear in North America and Europe essentially simultaneously — Teilhardina, an early primate, turns up across three continents within a few tens of thousands of years. Warmth had opened high-latitude forest corridors, and the animals used them. Many lineages also shrink markedly during the warmest interval, a dwarfing response to heat seen in several independent groups.