Smithsonian Institution
National Museum of Natural History: Paleobiology: Geologic Time: The Oligocene
Travel through Earth's history to learn about the Oligocene time period, which is characterized by the appearance of most of the living families of mammals.
PBS
Nova: A Brief History of Earth
This timeline is a good resource if you are looking for brief descriptions of the geologic periods. Descriptions include pictures of common organisms for each period and the range of time covered by each period.
Curated OER
Unesco: Argentina: Ischigualasto / Talampaya Natural Parks
These two contiguous parks, extending over 275,300 ha in the desert region on the western border of the Sierra Pampeanas of central Argentina, contain the most complete continental fossil record known from the Triassic Period (245-208...