Studies of horse evolution arose during the middle of the 19th century, and several hypotheses have been proposed for their taxonomy, paleobiogeography, paleoecology and evolution. The present contribution represents a collaboration of 19 multinational experts with the goal of providing an updated summary of Pliocene and Pleistocene North, Central and South American, Eurasian and African horses. At the present time, we recognize 114 valid species across these continents, plus 4 North African species in need of further investigation. Our biochronology and biogeography sections integrate Equinae taxonomic records with their chronologic and geographic ranges recognizing regional biochronologic frameworks. The paleoecology section provides insights into paleobotany and diet utilizing both the mesowear and light microscopic methods, along with calculation of body masses. We provide a temporal sequence of maps that render paleoclimatic conditions across these continents integrated with Equinae occurrences. These records reveal a succession of extinctions of primitive lineages and the rise and diversification of more modern taxa. Two recent morphological-based cladistic analyses are presented here as competing hypotheses, with reference to molecular-based phylogenies. Our contribution represents a state-of-the art understanding of Plio-Pleistocene Equus evolution, their biochronologic and biogeographic background and paleoecological and paleoclimatic contexts.

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Four neochoristoderan vertebral centra are described from the latest Cretaceous of New Jersey, USA. One specimen was recovered from the basal transgressive lag of the Navesink Formation in the area of Holmdel, New Jersey, and two others were recovered nearby and probably were derived from the same horizon. The fourth was recovered from the Marshalltown sequence in the vicinity of the Ellisdale Dinosaur Site. These vertebrae expand the geographical range of Late Cretaceous neochoristoderes in North America by over 2000 km further east, and represent the first neochoristoderan remains from the Atlantic coastal plain. To discern whether neochoristodere remains are to be expected in New Jersey, and elucidate why neochoristoderes are apparently so rare in Appalachia, we implemented ecological niche modelling to predict the range of suitable habitat for Champsosaurus, the only known genus of Late Cretaceous neochoristoderes. We found that in Appalachia, the ideal habitat of Champsosaurus probably existed slightly further north and west than the Atlantic coastal plain, and New Jersey is probably on or near the margin of this suitable habitat space. These results suggest that the occurrence of neochoristoderes in New Jersey is consistent with the habitat requirements of known Late Cretaceous neochoristoderes. These vertebrae may therefore represent the southern margin of a population of neochoristoderes that lived further inland, where latest Cretaceous sediments are not preserved. The continued recovery of material from Late Cretaceous deposits along the Atlantic coast, and review of existing collections, is encouraged to clarify the true distribution of neochoristoderes in Appalachia.

The metapodials of extinct horses have long been regarded as one of the most useful skeletal elements to determine taxonomic identity. However, recent research on both extant and extinct horses has revealed the possibility for plasticity in metapodial morphology, leading to notable variability within taxa. This calls into question the reliability of metapodials in species identification, particularly for species identified from fragmentary remains. Here, we use ten measurements of metapodials from 203 specimens of four Pleistocene horse species from eastern Beringia to test whether there are significant differences in metapodial morphology that support the presence of multiple species. We then reconstruct the body masses for every specimen to assess the range in body size within each species and determine whether species differ significantly from one another in mean body mass. We find that that taxonomic groups are based largely on the overall size of the metapodial, and that all metapodial measurements are highly autocorrelated. We also find that mean body mass differs significantly among most, but not all, species. We suggest that metapodial measurements are unreliable taxonomic indicators for Beringian horses given evidence for plasticity in metapodial morphology and their clear reflection of differences in body mass. We recommend future studies use more reliable indicators of taxonomy to identify Beringian horse species, particularly from localities from which fossils of several species have been recovered.

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Polar bears (Ursus maritimus) are among the Arctic species that are most threatened by climate change. However, little is known about the ecology of polar bears over extended temporal intervals (>50 years). The goal of my thesis is to determine whether historic polar bears from the Lancaster Sound subpopulation underwent ecological shifts in response to a changing Arctic climate throughout the 20 th century (1950s-1970s) using stable isotope analysis. Historic polar bears did not undergo significant dietary shifts, remaining apex predators. The consistent reliance on seals and whales as their primary prey indicates continued access to optimal hunting conditions (i.e., sea ice). There is evidence that suggests environmental changes occurred from 1950-1970. This thesis offers novel insights into the historical ecology of polar bears, and provides a long-term isotopic baseline for polar bear ecology that will enable future studies to assess ongoing ecological changes of modern polar bears.iii ACKNOWLEDGEMENTS First and foremost, I would like to acknowledge that Carleton University is located on the traditional unceded territory of the Algonquin Anishnaabeg People, and that the specimens used in this project were collected from the traditional territory of the Inuit. As settlers, we must make the collective commitment to make the promise and the challenge of Truth and Reconciliation real in our communities, to honour the Treaty Rights of all Indigenous Peoples, and bring justice for murdered and missing Indigenous women and girls across the country.I would like to thank my thesis supervisors, Dr. Danielle Fraser and Dr. Root Gorelick. I can say with absolute certainty that this thesis would not exist in its current form without their guidance and endless support. I would especially like to thank Dr.Fraser for reading every single draft of my thesis without fail, and always offering helpful comments and suggestions. I would not be the scientist I am today without Dr. Fraser's influence -she is one of the most talented and passionate scientists I have met, and I am extremely grateful to have her as my mentor. I thank the members of my defense committee, Dr. Clément Bataille, Dr. Joseph Bennett, and Dr. Rachel Buxton, for their support throughout my degree and helpful commentary on my thesis. I would also like to thank the following people for their contributions to this study: Dr. Kamal Khidas for providing access to the Zoology Collections and polar bear specimens at the Canadian Museum of Nature; Roger D. Bull for granting access to the Laboratory of Molecular Biodiversity; Dr. Seth Newsome and Dr. Nicu-Viorel Atudorei for conducting stable isotope analyses at the University of New Mexico; Marisa Gilbert for her aid in coordinating sample shipment and ordering laboratory materials; and Dr. iv Catherine Cullingham for chairing my defense. I thank my friends, family, and labmatesfor providing me with never-ending kindness, love, and support, throughout the completion of my degree and beyond. I especially thank my frien...