Eucyon Tedford and Qiu, 1996

TEDFORD R. H., WANG X. & TAYLOR B. E., 2009, Phylogenetic Systematics Of The North American Fossil Caninae (Carnivora: Canidae), Bulletin of the American Museum of Natural History 2009 (325), pp. 1-218 : 89

Eucyon Tedford and Qiu, 1996

Type Species: Canis davisi Merriam, 1911 .

Included North American Species: Eucyon davisi (Merriam), 1911 , and E.? skinneri , new species.

Distribution in North America: Late Clarendonian of Nebraska and Hemphillian of Kansas, New Mexico, Oklahoma, Texas, Arizona, Nevada, Oregon, California, and northern Mexico.

Revised Diagnosis: Eucyon has no autapomorphies but is distinguished from the fossil and living Vulpini and the Cerdocyonina by possession of synapomorphies also present in all other members of the Canina : frontal sinus invading base of postorbital process removing ‘‘vulpine-crease’’ or depression from dorsal surface of process; paroccipital process expanded posteriorly usually with salient tip; mastoid process enlarged as knob or ridgelike prominence; loss of foxlike lateral flare and eversion of dorsal border of orbital part of zygoma.

Primitive characters retained by Eucyon relative to those of most species of Canis are: frontal sinus less posteriorly extended, ends anterior to frontoparietal suture and does not completely invade postorbital process; supraoccipital shield fan-shaped, inion broad and not strongly overhanging condyles; I3 less enlarged relative to I2 with weaker posteromedial cingulum; M1 paracone and metacone subequal in size; M2 metaconule weak or absent, postprotocrista present; m1 entoconid and hypoconid usually not joined by transverse crest; angular process of mandibular ramus less expanded with smaller fossa for inferior pterygoid muscle; forelimb short relative to hindlimb, radius/tibia ratio less than 80%; and humerus often with entepicondylar foramen.

Derived features linking Eucyon with Canis include: zygomatic arch strongly arched rather than gently curved, and p4 with second posterior cusp.

Discussion: In general, the morphology of Eucyon is similar to that of Vulpes , as they share numerous primitive features. However, Eucyon , like the South American cerdocyonines, possesses a small frontal sinus that does not fully penetrate the postorbital process, and it does not extend as far posteriorly as in most species of Canis . Eucyon does share with Canis species two synapomorphies lacking in the cerdocyonines, namely, the presence of a second posterior cusp on p4, and the strongly arched zygoma.

In North America, Canis is not known until the late Hemphillian. Canis ferox Miller and Carranza-Castañeda (1998) tends to be morphologically intermediate between Eucyon davisi and Canis lepophagus . The former shows the derived enlargement of the frontal sinus that distinguishes it from E. davisi and supports its relationship to Canis .