Two species of extinct Simius. The bare faced-owl-eyed gibbon (Ambulator nudus) (one of the oldest ancestors of the species) It relagated itself in African forests. It was recognizable due of its colorful, red face which lacked most of the fur. Juveniles skin was of a dark grey, and the bright red was a sign of health in the individual. It had a stout tail, as the species was moderately aboreal, staying in trees during the night. It was primarily herbivorous but enjoyed the small prey and insect every now and then. It went extinct due of competition (especially with human ancestors) and strict diet. As well, it was remarkably shy and high-stung. It would easily give up its territory to competitors, and so it lost most of its territories. By the middle Pleistocene, it was extinct. Ambulator Is the oldest genus in the family Colacaridae, and consiscted of large, moderately aboreal primates.

The lion owl-eyed gibbon (Colacarisiumius aureum) name given due of the fluffy tip of their tail, which they used as a threat display by holding it high and swinging it wildly. A truy, fully nocturnal Simius, it had large, bulging orange eyed that made it a formidable predator. It fed on insects and fruits, but also hunted small birds, reptiles and mammals. Simius reached Australia (native place of Colacarisimius sapiens) through small rafts, and some instead settled in Madagascar, where this species is native from. It went extinct from introduced animals, like cats and rats, the pet trade and targeted hunting, as it was considered a pest since this cunning predator would even raid coops for chicks and eggs during the nocturnal hours. They were described as incredibly intelligent and highily energetic and regarded as loving companions. However, they did very poorly in captivity and often died from stress and inadequate diet.