Ectoypodus arctos: a new, northernmost Eocene Paleogene Multituberculate From Ellesmere Island

Northernmost global record for Multituberculata from the Eocene of Ellesmere Island, Arctic Canada

Authors:

Beard et al

Abstract:

Multituberculates are non-therian mammals that are reasonably well documented in Middle Jurassic to late Eocene terrestrial ecosystems, particularly in the Northern Hemisphere (Kielan-Jaworowska and Hurum, 2001; Yuan et al., 2013). In terms of their generic-level diversity, North American multituberculates reached their zenith during the early Paleocene (Puercan and Torrejonian North American land mammal ‘ages’ or NALMAs), although the group retained much of this diversity into the succeeding Tiffanian NALMA (Krause, 1986; Fox, 2005; Scott, 2005; Secord, 2008). Possibly as a result of ecological competition with rodents, which colonized North America at the beginning of the Clarkforkian NALMA (Dawson and Beard, 1996), multituberculate diversity decreased dramatically by the early Eocene Wasatchian NALMA (Krause, 1982, 1986; Krishtalka, 1984). As a result, although certain early Wasatchian sites yield surprisingly abundant samples of multituberculates (e.g., Silcox and Rose, 2001), only three genera of multituberculates have been reported from the Wasatchian of North America. Two of these, Ectypodus and Parectypodus, are members of the Neoplagiaulacidae, whereas the third, Neoliotomus, is referred to the Eucosmodontidae. By the late Wasatchian (Lostcabinian), multituberculates are rarely encountered, and only one species of Ectypodus has been reported from this interval in mid-latitude regions of North America (Stucky and Krishtalka, 1982). Multituberculates have not yet been described from the early middle Eocene Bridgerian NALMA, although the group is known to have persisted in North America until the late Eocene Chadronian NALMA (Krishtalka et al., 1982; Ostrander, 1984).

Fossil mammals from the Eocene Eureka Sound Group on Ellesmere and Axel Heiberg islands in the Canadian Arctic archipelago were first reported by Dawson et al. (1976). Subsequent work has greatly expanded our knowledge of the mammalian fauna from this rock unit, which remains the northernmost occurrence of early Cenozoic terrestrial vertebrates known globally (West and Dawson, 1977, 1978; West et al., 1977; McKenna, 1980; Dawson, 1990, 2001, 2012; Dawson et al., 1993; Eberle and McKenna, 2002; Rose et al., 2004; Eberle, 2005, 2006; Eberle and Greenwood, 2012). Among the more poorly documented mammalian taxa known from the Eureka Sound Group on Ellesmere Island is a single species of neoplagiaulacid multituberculate, which has been cited in faunal lists as Neoplagiaulax sp. for several decades (West et al., 1977; West and Dawson, 1978; McKenna, 1980). These references to Neoplagiaulax in the fauna from the Eureka Sound Group, which is widely regarded as late early Eocene in age (e.g., Eberle and Greenwood, 2012), conflict with the biostratigraphic distribution of Neoplagiaulax elsewhere in North America, where its youngest known occurrence is during the late Paleocene (specifically, late Tiffanian biozone Ti-5a of Secord, 2008:fig. 8). Here we describe the only known multituberculate specimen from the Eureka Sound Group in order to assess its affinities more precisely than has been the case previously. Subsequently, we comment briefly on the paleobiogeographic significance of this northernmost record for Multituberculata.  Dental terminology and measurements follow Scott (2003, 2005) and Secord (2008:fig. 2).