EXAMINATION OF THE PALEOBIOLOGY OF A RELATIVELY COMPLETE SPECIMEN OF MESOCYON

Mesocyon temnodon is an Oligocene Canid known from specimens collected in South Dakota, North Dakota, Wyoming, Colorado and Nebraska. It is a member of the Canid subfamily Hesperocyoninae, however as it is in an apparently paraphyletic genus its exact phylogenetic position is not yet clear. In the collections at the North Dakota Heritage Center and State Museum there is a mostly complete specimen (NDGS 64) that conforms favorably to Mesocyon temnodon even though some of the diagnostic characters are not visible. It is unusual that so much of the post crania is present, which allows for examination of details not usually possible in fossil species. This study examines some aspects of the paleobiology of this canid.

One of the most basic pieces of information that needs to be known about an animal is its body mass. This can then be used to estimate other aspects of its paleobiology. Using equations based upon several limb bone measurements, it was discovered that the NDGS specimen would have had a body mass between 3.56 kg and 5.05 kg in life, roughly similar to the extant Gray Fox (Urocyon cinereoargenteus). Another basic aspect of the biology of fossil animals that can be useful is its running speed. There have been many attempts to calculate running speed in fossil organisms, but a consistently accurate equation has yet to be discovered. Many of the modern analyses use measurements of the hind limbs, however NDGS 64 has incomplete femora, so most equations cannot be used. A comparative estimate can be made by looking at the lengths of the Humerus and radius. A cursorial predator will have a radius that is roughly equal in length to the humerus, and a stalking, pouncing predator will have a radius that is 70-85% of the humerus length. NDGS 64 has a radius that is approximately 79% of its humerus, fitting in with the stalking, pouncing hunting style. Studies have also been done using distal humerus morphology to determine hunting style based upon pronation ability (grappling vs running). When comparing NDGS 64 to other carnivorans it is consistent with having a more grappling style of humeral anatomy (broader articulations, larger muscle attachment points).