Tremacebus harringtoni

Tremacebus harringtoni is the type species of Tremacebus, an extinct genus of New World monkeys that lived in the Early Miocene, in the interval that South American palaeontologists call the Colhuehuapian. It is known from only a few fossils, among them a skull from the Sarmiento Formation in Patagonia. Researchers think it was related to the modern night monkeys, which it would have resembled, and it is placed here with the night monkey family Aotidae. It was about 1 metre (3.3 ft) long, with an estimated body mass of 1.8 kg (4.0 lb). Its eyes appear to have been smaller than those of the living species, and CT scans of the cranium suggest a relatively small olfactory bulb and a poor sense of smell compared with night monkeys. Taken together, these features suggest that it may not have been nocturnal, which would set it apart from the night monkeys it resembles.