Title: Life at the top of the greenhouse Eocene world—A synthesis of the Eocene vertebrate
fauna and flora in Canada’s High Arctic
By Jaelyn Eberle, University of Colorado Museum of Natural History and the Department of Geological
Sciences, CU-Boulder
Early – middle Eocene (~53 – 38 Ma) sediments of the Eureka Sound Group in Canada’s Arctic
Archipelago preserve evidence of lush rain forests, inhabited at times by alligators, giant tortoises and a
diversity of Eocene mammals, including primates, tapirs, and hippo-like Coryphodon. This biota reflects
a greenhouse world, offering a climatic and ecologic deep time analog of a mild ice-free Arctic. The
Eocene Arctic mammalian fauna (22+ genera) is unusual in its abundance and diversity of tapirs and
plagiomenids (rare elements in mid-latitude faunas), and absence of artiodactyls (cloven-hoofed
ungulates), early horses, and the hyopsodontid condylarth Hyopsodus. Isotope analyses suggest that the
large herbivores such as the hippo-like Coryphodon were year-round inhabitants in the Eocene Arctic
forests. Eocene Arctic macrofloras reveal a forested landscape analogous to the swamp-cypress and
broadleaf floodplain forests of the modern southeastern United States, and plant richness was comparable
to contemporaneous mid-latitude localities some 3500 km to the south, in the US Western Interior.
Surprisingly, however, nearly half of the Eocene Arctic plant taxa are endemic. Multiple climate proxies
indicate a mild temperate early–middle Eocene Arctic with winter temperatures at or just above freezing
and summer temperatures 20˚C (or higher), with high precipitation. At times, this high precipitation
resulted in freshwater discharge into a nearly enclosed Arctic Ocean basin, sufficient to cause
considerable freshening of the Arctic Ocean. Fluctuating Arctic Ocean sea level due to freshwater inputs
as well as tectonics produced temporary land bridges that allowed animals to disperse between North
America and both Europe and Asia, as evidenced by numerous shared mammalian genera among the
Holarctic continents. However, the peculiarities of the Eocene Arctic biota also highlight the need to
assess the Arctic as a potential source area for exotic plant and animal taxa.