Xenocyon texanus (Troxell), 1915

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 : 152

Xenocyon texanus (Troxell), 1915 Fig. 57A–C; appendix 3

Canis texanus Troxell, 1915: 627 .

Protocyon texanus: J.L. Kraglievich, 1952: 62 .

Protocyon texanus: Kurtén and Anderson, 1980: 172 .

Type: YPM 10058, fragment of a left ramus with canine, p1–p4, m1–m3 ( Troxell, 1915: fig. 18) ; paratypes: YPM 10058, right M1 lacking most of the paracone and metacone ( Troxell, 1915: fig. 20) ; left humerus ( Troxell, 1915: fig. 23); anterior scapular fragment; left metatarsal IV; right cuneiform; right pisiform. YPM Mylodon- Camel Quarry, head of Rock Creek, Tule Formation (late Irvingtonian ), Briscoe County, Texas .

Distribution: Know only from the type locality.

Revised Diagnosis: Distinguished from Xenocyon lycaonoides , the only other species of the genus to occur in North America, by slightly larger size, m1 talonid wider relative to trigonid; hypoconid more marginal on the talonid; and M1 metaconule more salient than in most X. lycaonoides .

Description and Comparison: Except for the relatively minor differences signaled in the diagnosis, the morphology of the holotype clearly allies this taxon with X. lycaonoides . The crown of the canine is broken, but enough remains to show that it was short and only gently recurved. The premolars are uncrowded, and the p2 is isolated by diastemata. The premolar crowns are short and broad across their posterior roots and, although p3 may have had a minute posterior cusp, at the present state of wear only p4 does so and it has a tiny second cusp that surmounts the cingulum. The tip of p3 lies just below p2 and its posterior cingulum lies below that of p4. The tip of p4 may not have reached the height of the paraconid of m 1 in the unworn state. The anterior face of the m1 curves backward, and wear has opened a broad carnassial notch. The trigonid of m1 is only slightly wider than the talonid, the metaconid is small, and the hypoconid, clearly the largest talonid cusp, is not as centrally placed on the crown as in X. lycaonoides or the smaller, early Pleistocene X. dubius of China. Much of the enamel is broken away on the lingual surface of the talonid, and that has carried away any remnant of the entoconid. The m2 has likewise been damaged lingually, but that does not obscure the small size of the metaconid relative to the protoconid and the lack of a distinct entoconid. There is no anterolabial cingulum. The m3 has a central cusp (protoconid), a ridge leading lingually from it and a tiny cusp (metaconid) at its lingual side.

The horizontal ramus is deep as in X. lycaonoides , and the premolar row is not deflected medially relative to the molars as in C. lupus . A large mental foramen lies beneath p1–p2, with a smaller one beneath the anterior root of p3. The masseteric fossa is deep anteriorly and ends just behind m3.

Discussion: Berta (1988: 98) questioned Kraglievich (1952) and Kurtén and Anderson’s (1980) assignment of Canis texanus to Protocyon Giebel, 1855 , citing the retention of the metaconid on m2, despite its loss on m1, as characteristic of species of the latter genus. She instead assigned this taxon to Cuon , further supporting the differences between the latter and Protocyon on cranial and mandibular grounds. However, she failed to note that C. texanus retains the m3, a feature lacking in all species of Cuon . The only large hypercarnivorous canine genus with the constellation of features described above is Xenocyon . Moreover, X. texanus lies morphologically close to X. lycaonoides of Arctic North America and possibly represents an extralimital variant of the widespread X. lycaonoides .