Leptocyon vulpinus (Matthew), 1907

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 : 22-25

Leptocyon vulpinus (Matthew), 1907 Figures 7, 8A–F, 9A–B; appendices 3, 4

Nothocyon vulpinus Matthew, 1907: 183 , fig. 2. Cynodesmus vulpinus: Macdonald, 1963: 211 .

Type: AMNH 12883, left ramus with i1–i2 broken and i3–m2 (fig. 8B–C), right partial ramus, fragmentary premaxilla-maxilla with I1–P1, P3, isolated P4 and M1 broken (fig. 8A), and fore- and hindlimbs including left humerus (fig. 9A), right partial humerus, left radius and ulna (fig. 9B), left partial tibia and distal part of fibula, articulated calcaneum and astragalus, and limb fragments from 4 miles below the post office, Porcupine Creek, referred to Harrison Formation (medial Arikareean) of South Dakota. Matthew (1907: 183) reported the type from the Lower Rosebud beds ; Macdonald (1963: 211) listed the type locality as ‘‘A.M.N.H. ‘Rosebud’ 7’’ and the containing rocks as the ‘‘Harrison formation’’.

Referred Material: Haystack Valley Member (revised, Hunt and Stapleton, 2004), medial Arikareean, John Day Formation, Wheeler County, Oregon. Base of unit, Crazy Woman Knob section, Northwest Museum of Natural History, Portland State University, NM 103/16, fragment of right ramus with m1–m2.

Recorded by the University of Nebraska as from Hemingford Quarry 7B, in the ‘‘ Upper Marsland Formation’ ’ (early Hemingfordian), Box Butte County, Nebraska: UNSM 25416 , right ramus with c broken, p2–m3 (p1 missing) ; UNSM 25611 , right ramus with c broken, p2–m3 (p1 missing) ; UNSM 25453 , right ramus with c broken, p3– p4, and m1 (p2 broken, p1, m2, and m3 alveoli). These specimens are from the Runningwater Formation following McKenna (1965: 10) that ‘‘the type Runningwater Formation is part of the same unit as that referred to as Upper Marsland by Schultz and others.’’

Runningwater Formation (early Hemingfordian), Dawes County, Nebraska: F:AM 99352, right isolated M1 from a tributary of Pebble Creek. F:AM 99350, left ramal fragment with m2 and m3 alveoli from Cottonwood Creek Quarry. From Dunlap Camel Quarary, 4.5 miles west of the old town of Dunlap, Dawes County , Nebraska: F:AM 49187, right ramus with c–m1, p1, and m2–m3 alveoli (fig. 8F) ; F:AM 49186, left partial ramus with p4–m3; F:AM 67994, left humerus; F:AM 67994A, left ulna; and F:AM 6799B, right ulna.

Distribution: Medial Arikareean of South Dakota and Oregon, early Hemingfordian of Nebraska.

Revised Diagnosis: Leptocyon vulpinus differs from L. douglassi and Leptocyon gregorii in its larger size, stronger and more distinct parastyle on M1, m1 with trigonid and talonid wider relative to length, and proportionally larger m2 with larger and more distinct paraconid. L. vulpinus differs from L. mollis in its larger size, as well as larger and taller crowned premolars.

Description and Comparison: Macdonald (1963: 211) placed this species ‘‘in Cynodesmus because the type does not have lingual cusps on the talonid on m1 between the metaconid and the entoconid, the posterior end of the talonid basin is not closed, and the hypoconid is larger than the entoconid.’’ These characters are also shared with Leptocyon , and the type of L. vulpinus differs greatly from the genotypic species of the hesperocyonine Cynodesmus ( C. thöoides , see Wang, 1994). The type of vulpinus is assigned to the genus Leptocyon , but it differs from all other species of the genus, especially from L. gregorii from strata of equivalent age in South Dakota, in its broad P4, larger M1 parastyle, and a proportionally larger m2 with a more distinct paraconid. The M1 parastyle is not only larger, but, unlike that of L. gregorii , it appears as a distinct cusp that surmounts the labial cingulum. The lower premolars are large, tall-crowned, and widely spaced. The elongation and height of the premolars approximate those of L. vafer but the premolars are more widely spaced in L. vulpinus . The lower first molar has a welldeveloped and somewhat salient metaconid and a large hypoconid that is much larger than the entoconid. The most notable difference between L. vulpinus and L. gregorii is the large, elongate m2. It is larger relative to m1 than in all other species (fig. 5). Moreover, its paraconid is a well-developed, distinct cusp and not a mere shelf or ridge. For this reason the large subequal protoconid and metaconid are less anteriorly situated than in L. gregorii . The Oregon specimen confirms these features of the m1 and m2.

These distinctive morphological characters make it possible to separate L. vulpinus from the broadly contemporaneous L. gregorii and to extend the temporal range of the species to include specimens from the Runningwater Formation of Nebraska. Four partial rami from the Runningwater Formation are referred to L. vulpinus . They show relatively large, elongate, tall-crowned premolars and a robust m1. Unfortunately, only one mandibular ramus ( UNSM 25416) possesses the m2. This m2 and an isolated specimen (F: AM 99350) also have a distinct paraconid. Two of the referred rami have the alveolus for m2, and these again indicate a relatively large tooth approximating the size of that of UNSM 25416.

A combination of primitive and derived characters is seen in the type of L. vulpinus . The shape of P4, the well-developed parastyle of M1, and the distinct paraconid on m2 are primitive characters. Postcranial elements of the type ( AMNH 12883, fig. 9A–B) also possess numerous plesiomorphic features shared with Hesperocyon . The humerus is long relative to the length of the radius, and the entepicondylar foramen is exceptionally large. The distal trochlea is slightly oblique to the shaft, and the lateral articular surface is about twice the width of the medial and the two are separated by a deep groove. Proximally, the greater tuberosity approximates that of the articular surface of the capitulum, and the lesser tuberosity is larger than that of Vulpes , with the two being separated by a prominent bicipital groove. An articulated radius and ulna of the type is short and robust and closely resembles that of Hesperocyon . Viewed anteriorly, the distal end of the radius is marked by prominent grooves for the extensor tendons. A prominent styloid process extends distally, and a medial radial exostosis is present intermediate in size between that of Hesperocyon and L. vafer . The distolateral surface bears a large laterally extended articular facet for the ulna. The ulna is robust, with the distal end especially heavy and with a large facet for articulation with the radius.

Incomplete elements of the tibia and fibula are also morphologically similar to those of Hesperocyon . The proximolateral condyle of the tibia is transversely broad and widely overlaps the shaft, with a large facet for articulation with the fibula. The distal end of the tibia has a prominent medial malleolus and deep articular grooves for the astragalus that are separated by a strong ridge. The distal end of the fibula articulates weakly with the tibia but possesses a strong articular facet for the astragalus.