Chrysocyon nearcticus, TEDFORD R. H. & WANG X. & TAYLOR B. E., 2009

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 : 84-87

Chrysocyon nearcticus , new species Figure 32A–D; appendix 3

Canis edwardii: Nowak, 1979: 84 .

Type: UA 12610, left partial ramus with i1, c (roots), p1–p2, p3 (roots), p4–m2, m3 (alveolus) lacking the posterior part of the coronoid process and the tip of angular process (fig. 32C–D) from UA locality Sand Wash 1, Gila Group (early or medial Blancan), 8 km north of Duncan, Greenlee County, Arizona.

Etymology: For its occurrence in the Nearctic zoogeographic province ( Sclater, 1859).

Referred Material: LACM ( CIT) 1680, anterior part of left ramus with parts of c, p1–p2, and associated incisors, and LACM ( CIT) 149, fragment of left horizontal ramus with p3–m3 (fig. 32A–B). These fragments seem to be parts of a single ramus as established by contacts of the lateral wall of the ramus and are treated as such in the following description: CIT locality 105, unnamed deposits (early Blancan), about 4.7 km north of Minaca, valley of the Rio Papagochic, 250 km west–northwest of Chihuahua City, Chihuahua, Mexico. These remains were referred to Canis edwardii by Nowak (1979: 84).

Aguanga Fauna, Temecula Arkose (early or medial Blancan), 26 km east of Temecula, Riverside County, California: F:AM 31854, left ramal fragment with p3.

Distribution: Early or medial Blancan (early Pliocene), southeastern Arizona and southern California; early Blancan, western Chihuahua, Mexico.

Diagnosis: Synapomorphies that unite C. brachyurus and C. nearcticus are: lower premolars large relative to size of lower carnassial with significant diastemata separating p2 from adjacent premolars; ramus relatively slender and elongate in premolar region and base of coronoid process long (distance from m3 to condyle) relative to height; lower carnassial with small metaconid and talonid with weak transverse crest; m2 with weak anterobuccal cingulum, crown large relative to m1 with metaconid subequal in size to protoconid. C. nearcticus is distinguished from C. brachyurus in that premolars have more primitively elongate form, not short and high-crowned as in C. brachyurus ; metaconid of m2 not disproportionally enlarged; and talonid wider relative to trigonid.

Description and Comparison: The rami referred to Chrysocyon nearcticus are very similar in size to those of Canis edwardii . Comparison of these taxa reveals the major points of difference as follows. First, the rami of Chrysocyon are relatively elongate and slender. These proportional relationships are most marked in the length and depth of the ramus below the canine and anterior part of the premolar row and in the great length of the ascending ramus (expressed as distance from the posterior wall of the m3 alveolus to the end of the condyle: 54.0 mm, UA 12610). The premolars are separated by diastemata and more slender, elongate, and higher crowned than in C. edwardii , yet large relative to the size of the molars. The p3 from Aguanga, California, is grouped here because of its slender but high-crowned form, and enough of the ramus remains to show the diastemata separating it from adjacent teeth. It shows a weakly differentiated cusp situated high on the rear of the principal cusp. The p4 has a strong posterior cusp and a second cusp is present in the holotype of C. nearcticus , but not the referred specimen. The anterior premolars seem to lack posterior cusps. These teeth resemble those of Canis and Eucyon , especially in having a second cusp on p4, and they contrast with the short, broad, and high-crowned premolars with low posterior cusp on p3–p4 found in Chrysocyon brachyurus . The p4 is higher than the paraconid of m1, unlike in C. edwardii and other large Canis species.

Chrysocyon species have relatively lower crowned carnassials than in Canis , with the paraconid in particular having a nearly vertical anterior border and being low relative to the protoconid. The metaconid is reduced and the talonid has a weak transverse crest between the hypoconid and entoconid. The m2 is large relative to the m 1 in the Chrysocyon species , and the anterolabial cingulum is weak when compared with Canis . Chrysocyon nearcticus has a relatively small metaconid on m2, only equal to the height of the protoconid. In C. brachyurus the m2 has a larger metaconid, equal in size to the protoconid. Its base markedly inflates the lingual border of the tooth. This may be an autapomorphy for the living maned wolf correlated with the development of relatively large molars. An early stage in this transformation is seen in C. nearcticus in which the m2 is large relative to the m1. Correspondingly, the m 3 in C. nearcticus is a relatively large oval tooth with subequal protoconid and metaconid and well-developed labial cingulum ( LACM ( CIT) 149: length X width, 6.5 X 5.5 mm).

Discussion: The discovery of fossil species closely resembling species of the living South American canids Cerdocyon and Chrysocyon in early Pliocene rocks of southern North America indicates the extent of the phyletic differentiation of the Canini at that time. The record of Chrysocyon described above rests only on the morphology of the lower jaws and lower dentition and hence not on the many cranial and postcranial autapomorphies recognized for the genus. To a certain extent the distinctive jaw and lower dental features represent a series of correlat- ed characters common to dolichocephalic canids (e.g., Canis simensis or Vulpes ferrilata ) and as such could represent parallel development of features in a taxon only distantly related to Chrysocyon . However, the correspondence in details of morphology are striking and the exceptions that distinguish C. nearcticus are features that are primitive for the Canini .

Fig. 32. Continued.