First record of eocene bony fishes and crocodyliforms from Canada's Western Arctic.
BACKGROUND
Discovery of Eocene non-marine vertebrates, including crocodylians, turtles, bony fishes, and mammals in Canada's High Arctic was a critical paleontological contribution of the last century because it indicated that this region of the Arctic had been mild, temperate, and ice-free during the early - middle Eocene (∼53-50 Ma), despite being well above the Arctic Circle. To date, these discoveries have been restricted to Canada's easternmost Arctic - Ellesmere and Axel Heiberg Islands (Nunavut). Although temporally correlative strata crop out over 1,000 km west, on Canada's westernmost Arctic Island - Banks Island, Northwest Territories - they have been interpreted as predominantly marine. We document the first Eocene bony fish and crocodyliform fossils from Banks Island.


RESULTS
We describe fossils of bony fishes, including lepisosteid (Atractosteus), esocid (pike), and amiid, and a crocodyliform, from lower - middle Eocene strata of the Cyclic Member, Eureka Sound Formation within Aulavik National Park (∼76°N. paleolat.). Palynology suggests the sediments are late early to middle Eocene in age, and likely spanned the Early Eocene Climatic Optimum (EECO).


CONCLUSIONS
These fossils extend the geographic range of Eocene Arctic lepisosteids, esocids, amiids, and crocodyliforms west by approximately 40° of longitude or ∼1100 km. The low diversity bony fish fauna, at least at the family level, is essentially identical on Ellesmere and Banks Islands, suggesting a pan-High Arctic bony fish fauna of relatively basal groups around the margin of the Eocene Arctic Ocean. From a paleoclimatic perspective, presence of a crocodyliform, gar and amiid fishes on northern Banks provides further evidence that mild, year-round temperatures extended across the Canadian Arctic during early - middle Eocene time. Additionally, the Banks Island crocodyliform is consistent with the phylogenetic hypothesis of a Paleogene divergence time between the two extant alligatorid lineages Alligator mississippiensis and A. sinensis, and high-latitude dispersal across Beringia.
University of Colorado Museum of Natural History and Department of Geological Sciences, University of Colorado at Boulder, Boulder, Colorado, United States of America.
Jaelyn J
JJ
Eberle
Department of Geological Sciences and Museum, Michigan State University, East Lansing, Michigan, United States of America.
Michael D
MD
Gottfried
University of California Museum of Paleontology, Berkeley, California, United States of America.
J Howard
JH
Hutchison
Department of Earth and Environmental Sciences, University of Iowa, Iowa City, Iowa, United States of America.
Christopher A
CA
Brochu
D000489:Alligators and Crocodiles; D000818:Animals; D001110:Arctic Regions; D002170:Canada; D005399:Fishes; D005580:Fossils; D005843:Geography; D062312:Islands