Weekly Spotlight: Daphoenus

29 05 2010

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.

Daphoenus sp. skeleton.

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.

D. vetus skull.

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.”

Daphoenus Reconstruction.

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).

-A probable limitation in the ability to pronate/supinate the forelimb.

These features strongly insinuate that Daphoenus and its kin were cursorial beasts which were either overwhelmingly carnivorous or omnivorous with a bias towards predation.

In this figurine diorama, a Moropus is harassed by a fairly large Daphoenus.

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.

Daphoenus skull reconstruction.

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.

Daphoenus reconstruction.

May the fossil record continue to enchant us all!

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9 responses

31 05 2010
Anonymous

What I want to know is how in the world the amphicyonids managed to avoid competition with the hyaenodontid creodonts in the Oligocene, and the borophagine dogs and large hesperocyonine dogs like Osbornodon in the Miocene.

31 05 2010
tanystropheus

Good question…

Have you considered consulting “Ask A Biologist?” I’m sure that Darren Naish & company will be able to offer some assistance.

http://www.askabiologist.org.uk/

31 05 2010
johannes

Another excellent post on one of my favourite prehistoric mammals, although that lone bear-dog that tries to attack the chalicothere looks somewhat, well, over-ambitious 😀

> The amphicyonids first emerged some 44 million years ago
> in Europe during the Mid-Eocene epoch before spreading into
> Asia and North America

Walking with Beasts (admittedly not the most scientific of sources) shows small amphicyonids in Oligocene Mongolia, and Probst (http://www.amazon.de/Deutschland-Urzeit-Ernst-Probst/dp/3572010578) has also claimed that large amphicyonids like *Amphicyon* were among the Asian invaders that caused the Grand Coupure of the European Oligocene. There is also an amphicyonid from Eocene China (see here: http://app.pan.pl/archive/published/app48/app48-293.pdf), while, on the other hand, the Eocene European *Simamphicyon* might be a miacid or a viverravid (http://taxonomicon.taxonomy.nl/TaxonTree.aspx?id=657028&tree=0.1&syn=1). All this suggests that an Asian, rather than European, origin of amphicyonids can’t be ruled out.

> before eventually being out-competed by the precursors
> of modern ursids, canines, and felines by the Pleistocene’s
> conclusion.

There were late Pliocene, or even Pleistocene Amphicyonids? Please tell me more!

31 05 2010
johannes

Oops, the second link does’nt work, try this:

http://app.pan.pl/archive/published/app48/app48-293.pdf

1 06 2010
tanystropheus

Thanks for the info, Johannes!

Unfortunately, the “pleistocene” reference was a typo of sorts on my part… sorry about that!

2 06 2010
Anonymous

“Have you considered consulting “Ask A Biologist?” I’m sure that Darren Naish & company will be able to offer some assistance.”

I tried. All I got was one person who started talking about how ancient ecologies might not be like ours at all, and never really answered my question in the first place.

“There were late Pliocene, or even Pleistocene Amphicyonids? Please tell me more!”

According to my sources (read: Wikipedia and some No. Am. paleontology books), amphicyonids seem to be one of those taxa which did quite well through the Miocene, only to suffer an abrupt extinction at the Miocene-Pliocene boundary, much like North American rhinos, oreodonts, bone-crusher dogs, and North American three-toed horses (except for Nannipus peninsulatis). Strange, it almost seems like there was a “cleaning house” of previously dominant taxa during the very latest Miocene and early Pliocene. Maybe these species were not as well adapted to the cooling climate?

3 06 2010
johannes

> What I want to know is how in the world the amphicyonids
> managed to avoid competition with the hyaenodontid creodonts
> in the Oligocene, and the borophagine dogs and large
> hesperocyonine dogs like Osbornodon in the Miocene.

Did they avoid competition? They might have clashed, like lions, spotted hyenas and hunting dogs do in modern Africa.

3 06 2010
Anonymous

I meant more of how did they avoid to survive in the same environment, feeding on what appears to be the same prey, in the same general niche for much of the mid-Cenozoic.

7 06 2010
Zach Miller

Ah, bear-dogs. Thanks for featuring them! I’ve always wondered why they weren’t more successful. Their niche seems to have been taken over by dog-dogs and hyenas, I think. I think that speaks to the great success of canids. They are quick to adapt and come pre-installed with plenty of dietary options. In fact, only a few dogs ever became really specialized: borophagines and one species of wolf, which both became bone-crushers.

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