Phylogenetics and biogeography of two new species of paromomyid plesiadapiforms from a unique, High Arctic ecosystem of Eocene Canada

Abstract

The Margaret formation of the Eureka Sound Group in the Canadian Arctic Archipelago samples a unique, warm temperate ecosystem with a polar light regime that dates to the early Eocene epoch ~ 53 Ma. Previous paleontological expeditions into this region have yielded a wide array of vertebrate taxa including early crocodilians and a diversity of mammals. Although crown clade primates have never been recovered from the Eocene of Arctic Canada, at least two new taxa of paromomyid plesiadapiforms occur there. This research aims to describe the Arctic paromomyids from Ellesmere Island and assess their phylogenetic relationships with respect to other members of this clade with the goal of reconstructing the paleobiogeographic affinities of these arboreal taxa and constraining the timing by which they colonized the Canadian Arctic. A phylogenetic analysis was completed using a morphological character matrix utilizing 63 dental characters scored for 17 taxa. A parsimony analysis completed using PAUP* suggests the two new paromomyid species are sister taxa that are highly nested within the Ignacius clade. These results suggest the Arctic paromomyids are closely related to mid-latitude North American paromomyid clades and are not specially related to the European genus Arcius. The nested relationship also suggests the Arctic taxa dispersed into high northern latitudes after the initial diversification of North American paromomyids during the Paleocene. The date for the lower faunal zone of the Margaret Formation (where most of the mammalian taxa occur) coincides with increasing temperatures during the Early Eocene Climatic Optimum (EECO). This suggests the northerly dispersal of the Arctic paromomyids may have been in response to rising global temperatures during the EECO. Further research on the new taxa will be focused on dental topography analysis to better understand the ecological adaptations that allowed for their survival in an ecosystem with a polar light regime.