The early apes were in general smaller and much more monkeylike than what we now think of as apes. Their skeletons show that they were quadrupeds, capable of climbing, rather than the specialized arm swingers and branch hangers that modern apes are. They came in all sizes and shapes, from the gorilla-sized Proconsul major and Turkanapithecus heseloni to the diminutive Micropithecus clarki. Some of the smaller varieties, such as Dendropithecus macinnesi, were beginning to specialize in arm swinging and were akin to the adaptation seen today in the South American spider monkey. Somewhere in the small-to-middle-size range of the proconsulid apes lies our ancestor--actually the common ancestor of the living apes and humans. It may be a species close to the relatively well-known species Proconsul africanus, a tailless climber the size of a small dog.

The forests in which the proconsulids lived was dense but far different from the rain forests of the Oligocene and preceding epochs. The early Miocene proconsulid site of Koru in western Kenya preserves the remains of a mature forest but one that was adapted to periodic dry conditions. The site of Napak in eastern Uganda is perhaps the driest of these early Miocene sites, and although a forest, it probably had open patches within it. Most of the fossils here were covered by an ash that erupted from a nearby volcano.