TROPICAL BRITISH COLUMBIA: THE EOCENE

A reconstruction of BC's Early Eocene by Julius Csotonyi

British Columbia is blessed to have many fossil deposits that date back to the Eocene. This is the time in our Earth's history when our world was much warmer — about 13 degrees above what we are experiencing today. The dinosaurs had gone extinct by this point and we begin to see the dawn of modern animals filling that void. 

In the earliest portion of the Eocene, wee proto-hedgehogs smaller than your thumb lived in the undergrowth of British Columbia's forests. They shared the forest floor with an extinct tapir-like herbivore in the genus Heptodon that looked remarkably similar to his modern, extant cousins but lacked their pronounced snout (proboscis). I'm guessing that omission made him the more fetching of his lineage.

In both cases, it was a fossilized jaw bone that was recovered from the mud, silt and volcanic ash outcrops in the ancient lakebed at Driftwood Canyon. And these two cuties are significant— they are the very first fossil mammals we've ever found from the early Eocene south of the Arctic.

How can we be sure of the timing? The fossil outcrops here are found within an ancient lakebed. Volcanic eruptions 51 million years ago put loads of fine dust into the air that settled then sank to the bottom of the lake, preserving the specimens that found their way here. As well as turning the lake into a fossil making machine (water, ash, loads of steady sediment to cover specimens and stave off predation...) the volcanic ash contains the very chemically inert (resistant to mechanical weathering) mineral zircon which we can date with uranium/lead (U/Pb). The U/Pb isotopic dating technique is wonderfully accurate and mighty helpful in dating geologic events from volcanic eruptions, continental movements to mass extinctions.

The name Eocene comes from the Ancient Greek ἠώς and καινός and means "dawn." Subtropical forests covered much of the southern coast of British Columbia. Instead of the Spruce, Cedar, Hemlock and Fir that thrive across BC today, we had palms and large ferns. We find their remains as fossils, providing important clues to our ancient climate. 

From the northwest of British Columbia in an arc to our southeast is a grouping of Eocene deposits we refer to as the Okanagan Highlands. These are Eocene lakebed sites that extend from Smithers in the north, down to the fossil site of Republic Washington just south of the US border. The grouping includes the fossil sites of Driftwood Canyon, Quilchena, Allenby, Tranquille, McAbee, Princeton and Republic.

These sites range in time from Early to Middle Eocene, and the fossil they contain give us a snapshot of what was happening in this part of the world because of the varied plant fossils they contain.

We can infer the difference in climates between the sites. McAbee was not as warm as some of the other Middle Eocene sites, a fact inferred by what we see and what is conspicuously missing. 

In looking at the plant species, it has been suggested that the area of McAbee had a more temperate climate, slightly cooler and wetter than other Eocene sites to the south at Princeton, British Columbia and Republic and Chuckanut, Washington. Missing are the tropical Sabal (palm), seen at Princeton and the impressive Ensete (banana) and Zamiaceae (cycad) found at Republic in north-central Washington, in the Swauk Formation near Skykomish and the Chuckanut Formation of northern Washington state.

In all, the Eocene lasted from 56 to 33.9 million years ago. There was no ice on the planet. There was no Antarctic ice sheet. There was no Greenland ice sheet. There were no mountain glaciers; no ice whatsoever. It was just too warm to have what we call a cryosphere, which are the frozen parts of our planet where water is in solid form— sea ice, lake ice, river ice, snow cover, glaciers, ice caps, ice sheets, and frozen ground. 

Without that ice to 'lock up' our abundance of water, sea levels were 70 meters higher during the Eocene— a significant difference that can be seen in the boundaries of our coastlines and what was and is waterfront property today.

Illustration: In a reconstruction of the early Eocene (52 million years ago) in northern British Columbia, a tapir-like creature from the genus heptodon drinks in the shallows, while a small proto-hedgehog stalks prey in the foreground. Created by the the hugely talented scientific illustrator, Julius T. Csotonyi and shared with permission.