Ancient DNA of the Toronto Subway Deer adds to the extinction list of ice age megafauna

The Late Pleistocene was a time of global megafaunal extinctions that were particularly severe in North America. The continent lost many mammal taxa, but the validity of several remains ambiguous, including a high proportion of Cervidae taxa. <i>Torontoceros hypogaeus</i> is represented by a single specimen (ROMM75974) discovered in 1976 during excavation work for the Toronto subway in Canada. The species was described based on its unique antler morphology, but the variable nature of that trait and the species near absence in the fossil record leads to uncertainty concerning its systematic relationships. We used ancient DNA to clarify the taxonomic relationship and evolutionary history of <i>T. hypogaeus</i>. We performed mitochondrial and whole genome analyses with related cervids and showed that ROMM75974 has a close affinity, but relatively high divergence from <i>Odocoileus</i> sister species. While some ambiguity remains, ROMM75974 could represent a distinct <i>Odocoileus</i> species to be included in the list of extinct North American taxa. This unique population was likely adapted to open landscape, which was rapidly replaced with dense woodland in this region at the end of the Pleistocene, highlighting the role of climate change in the extinction of megafauna biodiversity at the end of the ice age.