Rodents take over
A single pair of ever-growing incisors turns into the most species-rich order of mammals.
- When
- —
- Duration
- 21 million years
- Known to
- ± 2 million years
- Era
- Eocene, Cenozoic
Rodents appear at the end of the Paleocene and radiate explosively through the Eocene. The design is simple and enormously general: chisel-like incisors that grow continuously and self-sharpen because enamel covers only the front face, plus a jaw that can shift between gnawing and chewing positions. It supports almost any diet at almost any small body size. Rodents now account for about 40 per cent of all mammal species, and hystricognaths from this radiation later raft to South America and to Africa.