Letrero Formation

The Letrero Formation is a Late Miocene (Mayoan to Montehermosan in the SALMA classification) geologic formation in south-central Ecuador. The formation comprises lacustrine sediments with strong fluvial clastic input and contains siltstones and fine-grained sandstones.

Fossil content
The formation has provided fossils of:
 * Anadasypus aequatorianus
 * Caviomorpha indet.
 * Litopterna indet.
 * Toxodontia indet.