First fossil record of a Megatheriidae-Megatheriinae in the Early Hemphillian (Late Miocene) from San Gerardo de Limoncito, Curré Formation, Costa RIca

Abstract

We report the first record of Megatheriidae-Megatheriinae fossil record in Central and North America, which also represents the earliest record of a Megatheriidae-Megatheriinae outside of South America at 5.8 Ma, and before the closure of the Isthmus of Panama. The fossil record of the Megatheriidae record comes the from Curré Formation, Late Hemphillian (Hh3) (Late Miocene), San Gerardo de Limoncito locality, Canton of Coto Brus, Puntarenas Province, Costa Rica, and shows a combination of plesiomorphic and advance characters whose combination is unique among the Megatheriinae. These Megatheriidae remains are scarce and fragmentary, however, they have enough morphological information and key morphological characters to allow us to propose a new genus and species of Megatheriinae, Sibotherium ka gen. et sp. nov. Based on the morphology preserved in these remains, Sibotherium ka is more closely related to Megathericulus, Pyramiodontheroium or Anisodontherium than to the more advanced Megatheriinae genera Urumaquia, Megatherium or Eremotherium. We explain the early record of this xenarthran in Costa Rica by the presence of a land corridor established for short periods of time as a result of tectonic uplift or by a drop in sea level or a mixture of both at approximately 5.8 Ma in Southern Central America.