Tremacebus harringtoni is an extinct species of New World monkey from the Miocene. Tremacebus was about 1 metre (3.3 ft) in length, and would have resembled a modern night monkey, to which it may have been related. However, its eyes appear to have been smaller than the modern species, CT scans of the cranium suggest a relatively small olfactory bulb and poor sense of smell, compared with night monkeys. These features suggest that it may not have been nocturnal. Only a few fossils have been found, including a skull from Patagonia.