Good tidings and well-wishes!
At longtime reader Zach Miller’s request to cover an Amphicyonid “bear dog”, I’ve dedicated this post to one of the family’s most widely-preserved North American genera, Daphoenus sp.
The genus was named by the famed American anatomist and paleontologist Joseph Leidy in 1853, with the first scientifically-described species being D. vetus. Five additional species have subsequently been established: D. hartshorianus, D. lambei, D. ruber, D. socialis, and D. transversus.
Daphoenus has become the namesake genus for the Daphoneninae : one of the two known North American Amphicyonid subfamilies, with the other being the Amphicyoninae. According to Robert M. Hunt’s article in “The Evolution Of Tertiary Mammals In North America”:
“The Daphoeninae is considered here as a monophyletic North American endemic subfamily… [Its species are united by the following characters]: [Upper Molars or "M"]2-3 relative to M1 not enlarged in contrast to amphicyonines in which M2-3 are enlarged crushing teeth with amplified surface area; no reduction of premolars; p4 unreduced, often elongate, with squared posterior border; auditory bulla preserved only as an ossified ectotympanic crescent, loosely attached to the skull, without addition of any ossified entotympanic elements and without lateral prolongation into a bony external auditory meatus…; lack of expansion of the bulla posterior to the mastoid process; inferior petrosal venous sinus deeply excavated into edge of basioccipital; medial edge of petrosal in only slight contact with margin of basioccipital, not sutured to the basioccipital as seen in canids.”
In less technical terms, the Daphoeninae also bears the following non-exclusive generalized plesiomorphic characteristics:
-A generalized canine-like dentition.
-A relatively unspecialized and somewhat “feline” postcrania.
-Elongate cranium coupled with a short facial region of the skull.
-Presence of M3
-Lack of accessory cusps on anterior premolars.
-Elongation of lower limb elements (including the feet).
These features strongly insinuate that Daphoenus and its kin were cursorial beasts which were either overwhelmingly carnivorous or omnivorous with a bias towards predation.
As for Daphoenus itself, the skulls of it’s various species varied from a mere 14 cm in length (D. hartshorianus) to 24 cm in length (D. sp.) with the largest of these creatures rivaling a modern coyote in overall size. Some species are believed to have been sexually dimorphic, with the “males” sporting large canines and robust rostrums whilst the “females” maintain relatively small canines and gracile rostrums. The related species Brachyrhynchocyon sp. can be distinguished from this contemporaneous genus on the basis of the latter’s longer, narrower skulls and narrow premolars. Daphoenus is known from over sixty skulls (several of which contain associated lower jaws) along a number of postcranial skeletons, in addition to many isolated rostra, mandibles, and maxillae.
The amphicyonids first emerged some 44 million years ago in Asia during the Mid-Eocene epoch before spreading into Asia and North America in the early Oligocene before eventually being out-competed by the precursors of modern ursids, canines, and felines by the Miocene’s conclusion. It should be noted that while these “bear-dogs” exhibited canine dentitions and a degree of homogeneous ursid-like cervical anatomy, they are not considered to have been members of either family: it would appear that all three groups have merely emerged from a common ancestor.
May the fossil record continue to enchant us all!