The Oligocene Epoch was a geologic epoch that lasted from approximately 33.9 to 23 million years ago. As the Oligocene began, the Earth’s climate warmed slightly, forests and jungles receded, and grasslands spread across the planet. The early Oligocene is sometimes referred to as the “dawn of modernity”, because many modern groups of mammals, birds, reptiles and fish first appeared during this time.
During the Oligocene, there were several periods of global cooling known as ice ages or glacials. These ice ages reached their maximum extent towards the end of the epoch; by 23 million years ago, much of the Earth was once again covered in glaciers. The most notable event of the OligoceneEpoch was probably the Grande Coupure (“Great Break”), a mass extinction that occurred around 33.7 million years ago which wiped out over 70% of all mammal species present at that time.
The causes for this sudden die-off are still debated today; possible explanations include changes in sea level or temperature (both could have affected food availability), disease epidemics, or competition from newly evolved mammalian groups. Whatever its cause, this event had a profound effect on mammalian evolution; afterwards, only a handful of small primitive mammal groups survived until the beginning of the Miocene Epoch 10 million years later.
Amongst these were some early members of our own order – Primates – which first appeared in Africa during late Oligocene times (around 30 million years ago). Hominoids – apes and humans – would not appear until much later in geological history duringthe Miocene Epoch (approx.. 25-5 million years ago).