Originating in British Columbia, Canada, these Middle Eocene tree fossils exemplify some of the defining events of Paleobiology in the Tertiary (see discussion below). Three types of plant fossils are in association distributed front and back:

• Alnus parvifolia (Alder) - Family: Betulacaea
• Betula leopoldae (Birch) - Family: Betulacaea
• Metasequoia occidentalis (Dawn Redwood) - Family: Taxodiaceae (a Conifer that unlike the predominant evergreen Conifers was actually deciduous)

The Sassafras leaf is one half, with rest probably under the matric. The birch leaf would be over 5 inches if complete, and has nice venation. The alder and dawn redwood are on the back. In all, a pretty plant fossil association.

The Eocene was a period when flowering plants continued a massive radiation that began in the Paleocene Epoch. Plants thrived, and with that many animals, as new environmental niches were filled. The first grasses appeared with growth near the root as opposed to the tip, providing a renewable food resource and place of refuge for many animals. Small mammals radiated. Many new species of shrubs, trees and small plants appeared. A variety of trees thrived in a warm Eocene climate, including beech, elm, chestnut, magnolia, redwood, birch, and cedar, and more. The evolution of plants was providing a powerful selective pressure across the entire animal Kingdom, and many new symbiotic systems appeared.