16 Paleontology of North America

Added from Discipline submissions.

Monday, 9 March 2026
1:30 PM - 4:30 PM
RCC, 106

Paleobiology of a Relatively Complete Specimen of Mesocyon temnodon

Paper number: 16-8
Program: Technical Sessions
Time: 3:30 PM – 3:45 PM

Authors

Abstract

The Oligocene Canid, Mesocyon temnodon, is known from specimens collected in South Dakota, North Dakota, Wyoming, Colorado, and Nebraska.  It is a member of the subfamily Hesperocyoninae, however as it is in a likely paraphyletic genus its exact phylogenetic position is somewhat unclear.

In the collections at the North Dakota Heritage Center and State Museum there is a relatively complete specimen (NDGS 64) that conforms favorably to Mesocyon temnodon even though some of the diagnostic characters are not visible on the surface.  (However some have been confirmed via micro CT).   It is unusual in that so much of the post crania is present, this allows for examination of details not usually possible in many fossil taxa.  This ongoing study is examining several aspects of the paleobiology of this canid.  

The first aspect that was studied in detail dealt with the retractability of the claws.  This was studied because dogs in the Hesperocyoninae are sometimes described as “cat like” in their morphology and some of them are hypothesized to have retractable claws.  By examining the phalanges of the NDGS 64 specimen, three lines of evidence were tested to determine the retractability of the distal phalanges.  The size of the extensor and flexor processes, the depth of arc in the claw, and the morphology of the middle phalanx.  All three of these tests showed the claws to be not retractable.

Next, as many aspects of the biology of extinct animals is based upon body size, there are many different equations available for estimating body mass based upon various skeletal elements.  Several of these methods were used to estimate its body mass. Roughly 4-5kg in life.

Finally, the limbs of the Mesocyon specimen were studied to examine its ecological niche.  In spite of their fragmentary nature, it can be determined that the animal likely filled a similar ecological niche to the extant Grey Fox.

Geological Society of America Abstracts with Programs. Vol. 58, No. 1

doi: 10.1130/abs/2026SE-411828

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