The fossil-bearing sedimentary layers of the Abanico Formation were first discovered in the valley of the Tinguiririca River, high in the Andes of central Chile.
The faunal assemblage lends its name to the Tinguirirican stage in the South American land mammal age (SALMA) classification.
[2] Paleontologists knew the earlier sloth and anteater forebears of 40 mya, but no fossils from this previously poorly sampled transitional age had been seen.
Fossils of the Tinguiririca fauna include the chinchilla-like earliest rodents discovered in South America,[3] a wide range of the hoofed herbivores called notoungulates, a shrew-like marsupial and ancestors of today's sloth and armadillos.
Since then, in strata representing repeated catastrophic lahar events, more than 1500 individual fossils have been recovered from multiple sites in the region, ranging in age from 40 to 10 mya.