A POTENTIAL NEW CANID TRACK ICHNOSPECIES FROM THE MID-MIOCENE THUMB MEMBER OF THE HORSE SPRING FORMATION, LAKE MEAD REGION, SOUTHERN NEVADA

The Thumb Member of the Horse Spring Formation in the Lake Mead region of southern Nevada contains a wealth of fossil tracks from the mid-Miocene (Barstovian Land Mammal Age) of bird, camelid, felid, and canid origin. To date, no body fossils have been discovered within the Thumb Member. Therefore, fossil tracks and trackways provide us with the only glimpse into the faunal communities that once inhabited the region during the Barstovian LMA.

Here, we present a recently discovered canid trackway, likely exhibiting a trotting gait, recovered from the Echo Hills area just north of Lake Mead under a Bureau of Land Management permit. We are assigning these tracks to the ichnogenus Canipeda. There have been two ichnospecies of Canipeda previously described from Barstovian deposits in the southwestern United States: species A from the Barstow Formation in California and species B from the Thumb Member of the Horse Spring Formation. The tracks we describe here are notably smaller than the description provided for Canipeda sp. B, which has been attributed to a coyote-sized canid, likely a borophagine similar to the genus Tomarctus. We believe that the tracks we present here were likely produced by a smaller canid species about the size of a fox. Possible producers of these tracks include smaller borophagine genera such as Microtomarctus or possibly the early canine genus Leptocyon.