The Santa Cruz beds
Patagonian cliffs preserve South America's isolated fauna at its richest.
- When
- —
- Duration
- 1.5 million years
- Known to
- ± 500 thousand years
- Era
- Miocene, Cenozoic
The Santa Cruz Formation, exposed along the Atlantic coast of Argentina, records a warm, well-vegetated Patagonia around 17 million years ago and yields the best sample anywhere of South America's endemic mammals: native ungulates, marsupial predators, early sloths and armadillos, and platyrrhine monkeys. Darwin collected from related deposits on the Beagle voyage, and the giant extinct mammals he found there were among the observations that started him thinking about descent with modification.