PALEOGENE PERIOD ~ 66–23.03 million years ago

Scene featuring typical Eocene (Mid-Paleogene) flora and fauna

This period consists of the Paleocene, Eocene, and Oligocene Epochs. The end of the Paleocene (55.5/54.8 Mya) was marked by one of the most significant periods of global change during the Cenozoic, the Paleocene-Eocene Thermal Maximum, which upset oceanic and atmospheric circulation and led to the extinction of numerous deep-sea benthic foraminifera and on land, a major turnover in mammals. The Paleogene follows the Cretaceous Period and is followed by the Miocene Epoch of the Neogene Period. The terms 'Paleogene System' (formal) and 'lower Tertiary System' (informal) are applied to the rocks deposited during the 'Paleogene Period'. The somewhat confusing terminology seems to be due to attempts to deal with the comparatively fine subdivisions of time possible in the relatively recent geologic past, when more information is preserved. By dividing the Tertiary Period into two periods instead of directly into five epochs, the periods are more closely comparable to the duration of 'periods' in the Mesozoic and Paleozoic Eras.

As the Earth began to cool, tropical plants were less numerous and were now restricted to equatorial regions. Deciduous plants became more common, which could survive through the seasonal climate the world was now experiencing. One of the most notable floral developments during this period was the evolution of the first grass species. This new plant type expanded and formed new ecological environments we know today as savannas and prairies. These grasslands also began to replace many forests because they could survive better in the drier climate typical in many regions of the world during this period.

McAbee Fossil Beds, Tranquille Shale, Cache Creek, British Columbia, Canada, Geological Time: Eocene

Sassafras

Sassafras Hesperia

Order Laurales, Family Lauraceae

Size: Sassafras leaf is ~ 2 x 2 inches, and the shale 4.5 x 4.5 inches

This plate displays Sassafras hesperia leaf from the lacustrine deposits of the McAbee Flora of the Eocene of British Columbia, Canada. The genus is extant, albeit this species is extinct. The genus is also North America in the Eocene deciduous in most climates, though most members of its family are evergreens, an example of divergent evolution.