Warm blood evolves
Isotopes in fossil teeth suggest therapsids were already generating their own body heat.
- When
- Known to
- ± 10 million years
- Era
- Permian, Paleozoic
Oxygen isotope ratios in the teeth and bone of several Permo-Triassic therapsid groups indicate body temperatures elevated and stabilised well above their surroundings — evidence of endothermy tens of millions of years before the first true mammal. Warm blood is expensive, demanding far more food, but it permits sustained activity in cold and at night. It is one of the defining features of the lineage that becomes us.