Abstract – Dr. Jaelyn J. Eberle

Dr. Jaelyn J. Eberle, Department of Geological Sciences, University of Colorado, and Curator of Fossil Vertebrates, University of Colorado Museum of Natural History

Abstract

Today’s High Arctic is undergoing rapid warming, but the impact on its biota is not clear. As a climatic and ecologic deep time analog to better understand and predict the impacts of global warming on the Arctic biota, early Eocene (Wasatchian; ~52-53 Ma) rocks of the Eureka Sound Group on Ellesmere Island, Nunavut in Canada’s High Arctic (~79°N lat) preserve evidence of a diverse terrestrial ecosystem that supported dense, lowland swamp forests inhabited by alligators, turtles, snakes, primates, tapirs, and hippo-like Coryphodon. The fossil localities were just a few degrees further south and still well above the Arctic Circle during the early Eocene; consequently, the biota experienced months of continuous sunlight as well as darkness, the Arctic summer and winter, respectively.

As a result of over three decades of paleontological fieldwork, at least 23 mammalian genera in some 17 families and 11 orders, ranging from primates to carnivorans to tapirs and brontotheres, are represented in the early Eocene mammalian fauna from Ellesmere Island. The vertebrate fauna and flora of the early Eocene Arctic imply warmer, wetter conditions than at present, and recently published analyses of biogenic phosphate from fossil fish, turtle, and mammal estimate warm summers (~19 to 20 ˚C) and mild, above-freezing winters. In general, temperature estimates for the early Eocene Arctic are comparable to those in today’s temperate rainforests in the Pacific Northwest of the United States.

The early Eocene Arctic mammalian fauna shares most of its genera with early Eocene, mid-latitude faunas thousands of kilometers to the south in the US Western Interior, and several genera also are shared with Europe and Asia. Eocene mammalian fossils are considerably less abundant in the Arctic than at North American mid-latitude localities. However, rarefaction techniques can be used to compare diversity in samples of different size. When rarefaction curves are calculated for the early Eocene Locality 85 on Ellesmere Island, as well as similar-aged localities in Colorado and Wyoming, our results indicate that mammalian generic richness in the early Eocene Arctic is within the range of expected richness for comparably aged, mid-latitude North American localities. While mammalian diversity seems numerically comparable at mid- and high-latitude localities, there are notable differences in faunal composition. At the early Eocene mid-latitude localities, the ‘condylarth’ Hyopsodus is the most abundant taxon and artiodactyls (even-toed ungulates) occur in modest diversity, whereas neither taxon is known from the Eocene Arctic, where the enigmatic plagiomenids (often allied with Dermoptera or flying lemurs) are an abundant faunal element. An implication is that a relatively flat latitudinal diversity gradient for North American mammals existed during the early Eocene, which correlates with a reduced latitudinal temperature gradient for this time interval noted by paleoclimate studies. This is in stark contrast to today’s steep latitudinal diversity gradient in North American mammals.