Complete zygomatic arches in the Late Quaternary sloth Neocnus from La Altagracia province, Dominican Republic

Abstract

Specimens of the extinct sloth genus Neocnus recovered from northwestern La Altagracia Province, Dominican Republic exhibit a unique zygomatic arch. The arch consists of the jugal anteriorly fused to the maxilla and the zygomatic arch ligament fully ossified between the jugal and the zygomatic process of the temporal bone. Evidence of the novel ossification is seen in adult and juvenile individuals. This occurrence is also unexpected as Neocnus individuals are 40 times smaller than the next sloth genus (e.g. Nothrotheriops) with a secondarily complete arch. No known species of Neocnus exhibits any of these jugal and zygomatic features and thus these specimens may represent a new species.