They are geological epochs.
From the oligocene to the miocene.
upper ecocene to lower oligocene
The Oligocene Epoch.
This is called the Oligocene Epoch.
The nummulites mode of life was between the palocene and oligocene time periods.
Dinohyus ruled from the Oligocene epoch to the miocene, it ruled for about 13 million years.
There were five epochs in the Tertiary: Paleocene, Eocene, Oligocene, Miocene, and Pliocene.
North America, Asia and Europe was their home in the Oligocene and the earl Miocene period.
C. megalodon appears in the fossil register in the Late Oligocene, about 28 million years ago.
Texas' stone: Oligocene petrified palmwood Texas' gemstone: Texas blue topaz