STL Science Center

STL Science Center

28 September 2013

Hesperocyon the Early Dog

©Robert Bruce Horsfall
Hesperocyon is an interesting step beyond Miacidae, evolutionarily speaking. Miacidae represented the last taxa before the split between felines and canines and Hesperocyon represents the first taxa on the path to full fledged canines. The problem with instant recognition as a member of the canine family is that Hesperocyons are a noticeably transitional species between the mixture of feline and canine features of miacids and the canine features we expect to see in a canid. The heads of Hesperocyons appeared to be very canine like as the snout tapered and elongated anteriorly as we expect in canines. The extended downward arching necks of the animals were a little odd for canids, though we do have extant breeds of canine that have extended downward arching necks.

Cleophas C. O'Harra
Looking at the entire skeleton, it does not appear that either neck or the tail are exceptionally long compared to the early 20th Century fleshed out illustration. The skull is clearly becoming quite a bit more canine in its form and elongation. The premaxilla area of the skull is still a little abbreviated in comparison to modern canines and the canine (eye/upper jaw canine) teeth appear less embedded in the maxilla than do extant canine canines; in fact they appear to be inserted in a laterally sutured "pocket" of bone on the exterior of the maxilla. The skulls of Hesperocyons were shorter, as noted previously, and this may have additionally pushed out the canine teeth to a more lateral position; conversely it could be noted that the extending of the skull over time (disregarding breeds of dog that have been bred to possess exceedingly shortened snouts) allowed for the absorption of the lateral protrusion into the maxilla and streamlining (thinning) of the anterior aspect of the skull.

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