The First Tertiary Fossils of Mammals, Turtles, and Fish from Canada's Yukon

Abstract

Despite over a century of prospecting and field research, fossil vertebrates are exceedingly rare in Paleogene and Neogene rocks in northern Canadas Yukon Territory. Here, we describe the first records of probable Neogene vertebrate fossils from the territory, including tooth frag¬ ments of a rhinocerotid, a partial calcaneum of an artiodactyl, shell fragments of the pond turtle Chrysemys si. and tortoise Hesperotestudo, and a fragment of a palatine of Esox (pike). Although the tooth fragments cannot be identified solely by traditional paleontological means, we use tooth enamel micro structure, and primarily the presence of vertical Hunter-Schreger bands, to refer them to the Rhinocerotidae. As the only known record of the Rhinocerotidae in North Americas western Arctic, the tooth fragments from the Wolf Creek site support the hypothesis that the clade dispersed between Asia and North America across Beringia. The fossils are con¬ sistent with a Miocene age for the Wolf Creek site that is inferred from radiometric dates of the Miles Canyon basalt flows in the vicinity of the fossil locality. Further, the tortoise and pond turtle fossils indicate a mild climate in the Yukon at the time, consistent with the vegetation reconstructions of others that indicate a warmer, wetter world in the Miocene than today.

Post-Eocene Rhinocerotid Dispersal via the North Atlantic

“…E. itjilik also represents the highest latitude record of a rhinocerotid, to date, and the first occurrence in the Canadian Arctic Archipelago. The presence of rhinocerotids in the Western Low Arctic (i.e., Yukon Territory) during the Tertiary is apparent based on an enamel fragment that is not identifiable to genus or species 96 ; the much higher latitude occurrence of E. itjilik reported herein is represented by a nearly complete skeleton. The presence of a rhinocerotid in the High Arctic represents an interesting palaeoecological puzzle.…”

Using tooth enamel microstructure to identify mammalian fossils at an Eocene Arctic forest

“…HSB occur in the enamel of most large mammals and often are arranged horizontally. However, a few taxa, including rhinocerotoids, have vertical HSB [9,23,26]. HSB function as a crack-stopping device [27,28].…”

“…In the Canadian Arctic, rhinocerotoids are known from early Miocene sediments of the Haughton Formation on Devon Island (Dawson 1990) and from the Yukon [26]. Rhinocerotoids have vertical HSB in their tooth enamel that look somewhat like the vertical elements in Coryphodon-enamel [9,23,37].…”

Multiple hypotheses about two mammalian upper dentitions from the Early Cretaceous of Australia

“…NMV P252052 is a most perplexing tooth without unquestioned similarities to any vertebrate group. Two mammalian specimens to which NMV P252052 is compared in this analysis are the upper molars of Kollikodon ritchi, which has been regarded as either a monotreme (Pian et al 2016) or a haramyid (Musser et al 2019), and Obdurodon sp., an unquestioned monotreme (Woodburne and Tedford 1975). To avoid unintended implications of cusp homology, in references to the various cusps on the three taxa analysed here, their cusps are identified by different letters in Figs 6-8.…”