Eucyon skinneri, 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 : 90-104

Eucyon ? skinneri , new species Figure 33A–B; appendix 3

Type: F:AM 25143, partial mandible with i1–i3 alveoli and c–m2 (p1 and m3 alveoli and m2 broken) from the Hans Johnson Quarry, Merrit Dam Member, Ash Hollow Formation (late Clarendonian), Cherry County, Nebraska.

Etymology: Named in honor of the late Morris F. Skinner, Frick Curator Emeritus, American Museum of Natural History, who discovered the type and many of the other specimens used in this review.

Distribution: Late Clarendonian of Nebraska.

Diagnosis: Synapomorphies that unite Eucyon ? skinneri with E. davisi and other Canina are: m1 with well-developed entoconid and small hypoconulid. Primitive characters retained by E.? skinneri and differentiating it from E. davisi are: smaller size; shorter jaw; less elongate, lower crowned, and more robust premolars; p4 with small second posterior cusp; m1 trigonid proportionally shorter, protoconid lower crowned, hypoconid and entoconid lower crowned.

Description: The horizontal ramus retains a Leptocyon -like slenderness (depth beneath m1–m2 junction: 15.2 mm; beneath p1–p2: 10.5 mm) with the largest mental foramen beneath the short diastema separating p1 from p2, and a second foramen occurs beneath p3. The symphyseal union extends back to the posterior root of p2 where there is a slight inflection of the ventral side of the ramus. The canine is robust as in E. davisi and larger than that of the contemporaneous Leptocyon matthewi . The p1 alveolus shows that it was a robust, single-rooted tooth about the size of that of the smaller jaws referred to E. davisi . A very short diastema (2.6 mm) separates the canine and p1 alveolus; the length of this diastema is less than that of E. davisi . The p2 and p4 are more closely spaced; their transverse diameters are greater relative to their lengths than in E. davisi . The p2 consists primarily of a central cusp without a distinct posterior cusp. The p3 is intermediate in size to p2 and p4, and it has a weak anterior cusp, but a well-developed posterior cusp and a small cusp on the posterior cingulum. The p4 is similar to p3, but more robust, with a relatively stronger posterior cusp. It has a small second cusp on the posterior side of the first posterior cusp as seen in some E. davisi and in species of Canis .

The first lower molar is short and robust with the length less than that of E. davisi . The length of the trigonid is shorter relative to the length of the talonid than in the latter. The tooth is low-crowned with the heights of the protoconid and the hypoconid markedly lower than in E. davisi . The metaconid is strong and the talonid is wide and basinlike with a low hypoconid and entoconid. The height of the latter two cusps is less than in E. davisi . The metaconid is strong and the talonid is wide and basinlike with a low hypoconid and entoconid. The height of the latter two cusps is less than in E. davisi . The size of the hypoconid is proportionally smaller relative to that of the entoconid. As in E. davisi , the hypoconid and entoconid lack the transverse crest between them. There is an entoconulid differentiated from the postmetacristid as also seen in some individuals of E. davisi . Another character of note is the presence of an enlargement of the cingulum at the posterior base of the m1 hypoconid. This enlargement of the cingulum, or hypoconulid shelf, is not present in Leptocyon matthewi and is less developed than in E. davisi .

Discussion: The taxa to which E.? skinneri bears a close morphological resemblance are Leptocyon matthewi and Eucyon davisi . A comparison of the type of E.? skinneri with jaws of L. matthewi shows that its mandible and dentition are larger and more robust. It is, however, the morphological features of the m1 that really distinguish the type of E.? skinneri from Leptocyon and show its affinity with Eucyon . Compared to L. matthewi , the talonid of the m1 of E.? skinneri is proportionally wider with a better developed entoconid and an enlargement of the posterior cingulum. In Leptocyon , the m1 talonid is narrower and the entoconid is usually not as well developed as in the type of E.? skinneri . Like Leptocyon and Eucyon davisi , the type of E.? skinneri lacks a transverse crest between the entoconid and hypoconid of m1. The presence of a well-developed entoconid and a small hypoconulid or hypoconulid shelf are both derived characters that are shared with E. davisi . However, the p4 of the type has a distinct, but tiny, second posterior cusp characteristic of E. davisi . Lack of fuller knowledge of E.? skinneri causes us to question its assigment to the genus Eucyon .

Eucyon davisi (Merriam), 1911 Figures 27, 33C–T, 34A–Q, 35A–S, 36A–B, 39, 40, 43–44, 50–52, 60C, 61C; appendices 2–4

Canis (?) sp.: Merriam, 1906: 5, fig. 1.

Canis (?) davisi Merriam, 1911: 242 .

Leptocyon shermanensis Hibbard, 1937: 460 . Canis condoni Shotwell, 1956: 733 .

Eucyon davisi: Tedford and Qiu, 1996: 36 .

Type: UCMP 545, M1–M 2 in a fragment of a right maxilla (fig. 33I) that Merriam designated the type of C. (?) davisi in 1911: 6 ‘‘was obtained between Cottonwood Creek and Birch Creek in the southeast corner of Wheeler County, Oregon (Locality No. 887, Univ. Calif. Coll. Vert. Paleo.). At this locality the Mascall Formation is capped by the Rattlesnake beds. This specimen was obtained on an exposure of Mascall beds immediately below a Rattlesnake outcrop. It was not in the matrix, and we cannot be absolutely certain that it had not originally come from the Rattlesnake beds above.’’

Referred North American Material: Thousand Creek Formation (early Hemphillian), CIT locality 63, Humboldt County, Nevada: LACM 55210, left ramal fragment with p4; LACM 55209, right ramal fragment with m2; LACM 55208, left ramal fragment with p2 root–p4; LACM 55207, right ramal fragment with c–p1 alveoli, p2–p3 broken, and p4; and LACM 55206, left maxillary fragment with P2–P3 alveoli, P4, M1–M2, right maxillary fragment with M1 broken–M2. Line Quarry, Humboldt County, Nevada: F:AM 49286*, left maxillary fragment with P2 alveolus, P3 and P4 broken. LACM locality 1221, Hum- boldt County, Nevada: LACM 103220, left ramus with c–p3 alveoli, p4–m1, m2 alveolus. Thousand Creek, Humboldt County, Nevada UCMP locality V69113 , UCMP 112197, right ramus with c alveolus, p1–p2 (broken), p3 (alveolus)–p4, m1; and UCMP locality V78064 , UCMP 121862, left M1.

Juniper Creek Canyon, Grassy Mountain Formation (early Hemphillian), Malheur County, Oregon: UO 19027, right isolated M1; UO 26743, right partial ramus with p1– m2, UO locality 2451; and UO 19950, left partial maxilla with M1–M2, UO locality 2469.

Little Valley, Grassy Mountain Formation (early Hemphillian), Malheur County, Oregon: UO 26742, fragments of skull including partial premaxilla with I1–I3, right and left partial maxillae with P1–M2 (fig. 33G), right (fig. 33E–F) and left rami with i1–m3, detached teeth including two canines, much of the atlas and axis vertebrae, scapula, humerus fragment, distal ends of radius and ulna, scapholunar, magnum, four metacarpals, and phalanges, UO locality 2381.

Hoffman Blowout, Shutler Formation (Late Hemphillian), 6 miles southwest of Boardman, Morrow County, Oregon: LACM 55212, right isolated m1.

McKay Reservoir , UO locality 2222 (late Hemphillian), Malheur County, Oregon: UO F3241 , left ramus with c–m1 alveoli, m2, m3 alveolus (type of Canis condoni Shotwell , figured by Shotwell, 1956: fig. 6K, this paper fig. 33C–D, with UO F2353 , m1, inserted into alveolus) ; UO F2353 , isolated m1 (figured by Shotwell, 1956: fig. 6L, this paper fig. 33C, inserted into UO F3241 ) ; UO F2727 , right isolated P4 (fig. 33H) ; UO F2107 , left isolated P4 ; UO F3672 , right isolated P4 ; UO F3254 , left isolated m2 ; UO F3264 , isolated lower incisor ; UO F3672 , right isolated P4, UO F3254 , left isolated m2 ; UO F3264 , isolated lower incisor ; UO F2458 , isolated p2 ; UO F3266 *, isolated p2 ; UO F3262 , broken canine ; and UO F3253 , isolated unerupted C. SDSM locality V802: SDSM 13127 *, left ramus with alveoli of c– p4, m3, and crowns of m1–m2 ; and SDSM 57973 *, left maxillary fragment with alveolus of P3, crowns of P4 and M1–M2 .

Optima Local Fauna, Ogallala Group (late Hemphillian), near Cuymon, Texas County, Oklahoma: F:AM 62961-I, -N, -O, three isolated m1; F:AM 30397*, left ramus with p3–m2 alveoli; F:AM 30427*, right ramus with p1, p2–p4 alveoli, left ramus with p3–p4, m1 (alveolus); F:AM 30393*, right ramus with m2 broken; F:AM 30394*, partial left ramus with broken c–p4; F:AM 62929, left ramus with p2–m1; F:AM 62922*, right ramus with c, p2–m2; F:AM 62936, left ramus with p2–m1; F:AM 62937, left ramus with c, p1 alveolus, p2–p3, p4 alveolus, and m1; F:AM 72802, left femur, left tibia, tarsal bones, metatarsals II–V, phalanges; F:AM 72803, right radius; F:AM 72803A, right radius; F:AM 72804, left metacarpal II; F:AM 72804A, right metacarpal V; F:AM 72805, right metatarsal III; F:AM 62932, right ramus with p3–m3 (fig. 33P–Q); F:AM 62930, left ramus with p2–p3, m1; F:AM 62934, left and right rami with p3, m1–m2; F:AM 62950, right ramus with p3 broken– m1; F:AM 62951, right ramus with c–m1 (fig. 33R–S); F:AM 62952, partial left maxilla with p2–p3, p4 (broken), m1; F:AM 62958–62958C, isolated p4s; F:AM 62954, left maxilla with C–M2 (fig. 33T); F:AM 62960, isolated M1; F:AM 62953, left maxilla with P4, M1–M2 broken; and F:AM 62933 fragments of right and left rami, c, p2–p4, m1–m2.

Chamita Formation (late Hemphillian), Rio Arriba County, New Mexico: F:AM 27485, left ramus and right ramal fragment with c–m3 (p1 alveolus and m2 broken), 5 miles north of San Juan ; F:AM 62836, right and left partial maxillae with P3 and M1–M2, right ramus with i1–m1, m2 broken, and calcaneum, 5 miles north of San Juan; F:AM 62835, left maxillary fragment with M1–M2, San Juan locality, upper tuffaceous zone; F:AM 27375, mandibular fragment and symphysis with i1–p3 broken and p4, Battleship Mountain .

Edson Quarry, Ogallala Group (late Hemphillian), Marshall Ranch, Sherman County, Kansas: KUMP 3608, right partial ramus with incisor alveoli, c–p4, and m1 broken (type of Leptocyon shermanensis Hibbard , figured by Hibbard, 1937: fig. 1); F:AM 49464, palate with C–M2 (fig. 33J–K); F:AM 49458, left maxilla with P3–P4; F:AM 49462, left ramus with c, p2 broken–m2 (fig. 33L–M possibly part of the holotype mandible of L. shermanensis ); F:AM 49463, right ramus with p3, m1–m2; F:AM 49466, left (fig. 33N–O) and right rami with p1–m3; F:AM 49461, right ramus with dp2–dp4, m1–m2 erupting, calcanea, scapula fragment, right metatarsals III–V, left metatarsals II–IV, phalanges; F:AM 49465, left and right rami with c–m2; F:AM 63183, partial occiput (fig. 34Q); F:AM 63184, isolated canine; F:AM 49456, isolated incisors, canines, M1–M2, left and right rami, p1–m2, isolated teeth, left tibia, left limb, calcaneum, astragalus, left metatarsals II–V, tarsals, proximal and distal phalanages, right femur, right tibia, right fibula, calcaneum, astragalus, right metatarsals II–V, phalanges, vertebrae; F:AM 49457, right ramus with m1–m2 both broken; F:AM 49470, palate with C–P4, deciduous teeth, vertebrae; F:AM 49469*, right ramus of old individual with p2 broken–m3, m2 broken; F: AM 72828A, left tibia; F:AM 72832, calcaneum; F:AM 72832A, astragalus; F:AM 63177, calcaneum; F:AM 63188, distal end radius; F:AM 63177, left metatarsal IV; F:AM 72830, right metatarsal IV; F:AM 63186, right metatarsal V; F:AM 63187, right metatarsal II; F:AM 63185, left metacarpal II; F:AM 72826, left radius, right metacarpals II–V, distal end of ulna, phalanges, and sesamoid; F:AM 63177B, distal phalanx; F:AM 63190, medial phalanx; F:AM 63176, proximal, medial, and distal phalanges; F:AM 63181, distal phalanx; F:AM 72829, left metacarpal V; F:AM 63179, distal phalanx; F:AM 72831, right metatarsal V; and F:AM 63189, right metatarsal IV. F:AM 63178, left upper canine, 2 miles south of Main quarry, Marshall Ranch (Rhino Hill Quarry).

Goodnight beds, Ogallala Group (late Hemphillian), Goodnight area, Armstrong County, Texas: F:AM 49319, left partial ramus with p2 alveolus, p3–p4, and m1 alveolus, Hill Quarry, 20 miles southwest of Claude; F:AM 49322, right maxilla with M1– M2, McGehee Place Quarry; and F:AM 49320, right isolated P4 and left isolated M1, Christian Pit 2.

Miami Quarry (5 Coffee Ranch Quarry), Ogallala Group (late Hemphillian), 8 miles east of Miami, Hemphill County, Texas: F:AM 23373, right maxilla with C–P1 alveoli and P2–M2 (fig. 35J–M) and right partial ramus with p1 alveolus–m1; F:AM 23353, left partial ramus with p3–m2, m3 alveolus (fig. 35H–I); F:AM 23374, left partial maxilla with P1–P4 alveoli and M1–M2; F:AM 23373A, left isolated P4; F:AM 23376F, right isolated M1; F:AM 23374B*, m1 broken; F:AM 23376B*, m1 broken; and F:AM 23376C, right m2.

Axtel locality, UCMP locality V5319, Ogallala Group (latest Hemphillian), Rendall County, Texas: UCMP 112196, right isolated M1.

Rentfro Pit, Ogallala Group (Latest Hemphillian), 4 miles southwest of Channing, Hartley County, Texas: F:AM 62981, crushed skull with P1–M2 (fig. 35N–O), right partial ramus with p2–m2 (p3 broken), m3 alveolus (fig. 35P–Q), and atlas: and F:AM 62980, left partial ramus with m1 broken– m3.

Gravel pit on the Virgil Clark place (latest Hemphillian), 2.5 miles southeast of Higgins, Texas, in Ellis County, Oklahoma: F:AM 22296, right ramal fragment with p4–m1 alveoli and m2.

Bird Bone Quarry, Big Sandy Formation (late Hemphillian), near Wikieup, Mohave County, Arizona: F:AM 63007, partial skull with P3–M2; F:AM 63004, anterior portion of skull with P2, P4–M2 (fig. 34D–E), and isolated teeth; F:AM 63039, anterior portion of skull with P2–M2; F:AM 63019, partial skull with P1–M2, left and right rami with p3–m3; F:AM 63038, palate with P2–M2, left and right rami with p2–m2, isolated c; F:AM 63033, left and right maxillae with P4–M2; F:AM 63034, left and right maxillae with P1– M2 (P3 alveolus) and left ramus with p2–p3; F:AM 63020, left and right maxillae with C, P4–M2, left and right rami with m1, vertebrae; F:AM 63012, right maxilla with P2 and P4; F:AM 63021, right maxilla with C, P4– M2; F:AM 63013, left and right maxillary fragments of old individual with P2–P4 and M1–M2; F:AM 62999, left ramus with p4 broken–m2; F:AM 63000, right ramus with m1–m2; F:AM 63001, left ramus with c–m2; F:AM 63002, left ramus with p3 broken–m2, m1 (broken); F:AM 63015, left and right rami with p1–m1; F:AM 63016B, right ramus with p3–m2; F:AM 63016C, left ramal fragment with m1; F:AM 63016D*, right ramus with p1–p2; F:AM 63022, left ramus with m1; F:AM 63023, right partial ramus with p4–m2; F:AM 63025, left ramus with p2–m1; F:AM 63026, left ramus with p2–m2; F:AM 63027, right ramus with p2, p4–m1 (all broken), and m2; F:AM 63028C, left partial ramus with p4–m1 broken, m2; F:AM 63041, left ramus with p2–m2; F:AM 63042, right ramus with p1–m3; F:AM 63051*, left and right rami with m1; F:AM 63056, left and right (fig. 35D–E) maxillae with P2, P4–M2, and left (fig. 35F–G) and right rami with c, p3–m2, isolated teeth; F:AM 63057, right maxilla with P4–M2, left and right rami with m1; F:AM 63063, right maxilla with P4–M2; F:AM 63046, left and right rami with p3 broken–m2; F:AM 72593*, left ramus with p3–p4 (all broken), m2, and all alveoli; F:AM 72594*, left ramus, all alveoli; F:AM 72595*, right ramus with m2; F:AM 72605, right ramus with p1–p4; F:AM 72609*, right ramus with p3; F:AM 63010, crushed skull (fig. 34F, H) and mandible (fig. 34G, O) with complete dentition and articulated skeleton (fig. 36A–B); F:AM 63058, left and right (fig. 35A) maxillae and premaxilla with I3 broken, P2–M2, left and right (fig. 35B–C) rami with p2–m1, isolated canine, and right m2; F:AM 63005, anterior portion of skull with P3–M1 (fig. 34A) and cranial fragment (fig. 34P); F:AM 63191, left maxilla with M1, left and right partial rami with all alveoli, distal femur cap, distal end of tibia, metatarsals II, IV–V, metapodial fragments, proximal and distal phalanges, two isolated p4, isolated m1 broken, vertebrae, cuneiform, cranial and maxillary fragments; F:AM 63192*, left partial ramus with p4–m3 alveoli, radius, caudal vertebrae; F:AM 63196, calcaneum; F:AM 63198, metatarsal II; F:AM 63199*, isolated left m1; F:AM 63203*, isolated right p2 and premolar fragments; F:AM 63200*, right p4, metacarpals III (left and right), V, and II (left and right partial), distal end of tibia, proximal ends of left and right radius, proximal end of ulna, proximal and medial phalanges, vertebrae, limb and dentary fragments; F:AM 63201, astragalus and cuboid; F:AM 63202, astragalus; F:AM 63206, left calcaneum and astragalus, left metatarsals II–IV, one proximal, two medial, and two distal phalanges, right metatarsals II–III, V (broken), two proximal, two medial, two distal phalanges, carpals, distal end left and right tibiae, partial pelvis, caudal vertebrae; F:AM 72555, right humerus; F:AM 72558, right humerus; F:AM 72559, right humerus; F:AM 72561, right radius; F:AM 72562, left radius; F:AM 72563, left radius; F:AM 72564, left radius; F:AM 72567, right ulna; F:AM 72568, right ulna; F:AM 72570, left femur; F:AM 72572, right tibia; F:AM 63019A, right humerus, proximal end left humerus, left femur, distal head right femur, right tibia (three pieces), left tibia, left and right calcanea, right astragalus, distal ends of three metapodials, three phalanges, scapula and pelvic fragments, vertebrae; F:AM 72583, left metacarpal IV; F:AM 72583A, left metacarpal IV; F:AM 72584, right metacarpal V; F:AM 72584A, left metacarpal V; F:AM 72585, left metatarsal II; F:AM 72585A, right metatarsal II; F:AM 72586, left metatarsal III; F:AM 72587, left metatarsal III, F:AM 72586A, left metatarsal V; F:AM 72587A, right metatarsal II; F:AM 72587B, left metatarsal III; F:AM 72588, right metatarsal IV; F:AM 72589, right metatarsal IV; F:AM 72589C, left metatarsal IV, right metatarsal V; F:AM 72590, left metatarsal V; F:AM 72590A, left metatarsal V; F:AM 72590B, left metatarsal V; F:AM 72573, left metatarsals II–V; F:AM 72575, left metatarsals II–V, two phalanges; and F:AM 63207, calcaneum and astragalus.

Clay Bank Quarry, Big Sandy Formation (late Hemphillian), near Wikieup, Mohave County, Arizona: F:AM 63031, crushed partial skull with C–M2, left and right rami with p2–m2; F:AM 63008, partial skull with P4 broken–M2, right ramus with p3 broken– m2, distal and left humerus, proximal end right femur, calcaneum, phalanges; F:AM 63008X, right ramus with p2 broken, p4 broken, m1, right ramus with p3–m2 (p4 broken), left maxillary fragment with P4–M1 broken; F:AM 63008Y, anterior portion of skull with P2, P4–M2; F:AM 63006, right maxilla with P4, M2, cranial fragments; F:AM 63011, left maxilla with P2, P4–M2; F:AM 63009, skull with P3–M2 (fig. 34P), two astragali, phalanges, and caudal vertebrae; F:AM 63009A*, right ramus with p4 broken–m2; F:AM 63009C*, right ramus with p2 broken, m1 broken; F:AM 63003, left and right rami with p1–m3; F:AM 63009B, left ramus with c–m2 (fig. 34M–N); F:AM 63014, left ramus with p2–m1; F:AM 63016A, right ramus with p3 broken–m2; F:AM 63018, left ramus with p2–m3 (p3 broken); F:AM 63024, right ramus with p3– p4 both broken, m1–m2, and m3 broken; F:AM 63028, isolated m1; F:AM 63028A, left ramus with p1–m2; F:AM 63028B, left ramus with p2–m1; F:AM 63028D, right isolated m1; F:AM 63028E, left ramus with m1–m2; F:AM 63028M right ramus with p2– p3, p4 alveolus, m1–m2, m3 alveoli; F:AM 63028G, left ramus with p4–m1; F:AM 63028H, right m1; F:AM 63028I, right ramus with m1–m2; F:AM 63028J, right ramus with p3 broken–m1 and m2 broken; F:AM 63028K*, right ramus with p3 broken, m1; F:AM 63030, anterior portion of skull and ramus with C–M3, limb fragments; F:AM 63029, left ramus with p3–m2; F:AM 63032, right ramus with m1–m2; F:AM 63036*, right isolated m1; F:AM 72604, left ramus with c–m2; F:AM 72592, left ramus with p2– m2; F:AM 72596, right ramus with p1–m2; F:AM 72601, left ramus with p4 broken, m1– m2; F:AM 72591, right ramus with c, p2–m2; F:AM 72597, left ramus with p2 broken–m1 (p3 broken); F:AM 72602, left ramus with p3–m1; F:AM 63047, right ramus with p4– m2; F:AM 63049, left ramus with m1–m2; F:AM 63044, right ramus with p1–p2, p4–m2 all broken; F:AM 63045, right ramus with c, p1 alveolus, p2–p4, m1, m2 broken; F:AM 63043, right ramus with p1–m2; F:AM 63017, left m1; F:AM 63017A, left ramus with p2–m1; F:AM 63197, metatarsal IV, phalanges; F:AM 72557, distal end right humerus; F:AM 72560, right radius; F:AM, left radius; F:AM 72570A, right femur; F:AM 72571, left tibia; F:AM 63208, left ulna; F:AM 63009D, left humerus; F:AM 63009E, right humerus; F:AM 63009F, right ulna; F:AM 63009G, distal end left radius, proximal end right radius, and partial proximal end left ulna; F:AM 63009H–L, right femur; F:AM 63009M, left femur; F:AM 63009N, left tibia; F:AM 63009O, right tibia; F:AM 63009P, left tibia; F:AM 63009Q–R, right tibii; F:AM 63009S, calcaneum, astragalus, right metatarsals II, III, V, phalanges, scapula and pelvic fragments, vertebrae; F:AM 63017B, left and right humeri; F:AM 63017C, proximal end right radius, distal end left radius; F:AM 63017D, left and right ulnae; F:AM 63017E, proximal end right femur; F:AM 63017F, proximal end left and right tibiae; F:AM 63017G, right tibia; F: AM 63017H, calcaneum, astragalus, isolated teeth, metapodials, scapula fragments, vertebrae; and F:AM 63208, left ulna.

Grey’s Ranch Quarry, Big Sandy Formation (late Hemphillian), Mohave County, Arizona: F:AM 63040, right ramus with c– p4, m1 broken; F:AM 63040A, right partial maxilla with M1–M2 (associated with F:AM 63040 and possibly one individual); F:AM 63048, left ramus with p3–m3; F:AM 72603, right maxilla with C broken, P2 broken, right ramus with p4–m2 (m1 broken); F:AM 63204, astragalus; F:AM 63204A, astragalus; F:AM 63204B, calcaneum; F:AM 63205, astragalus; F:AM 63205A, astragalus; F:AM 63205B, calcaneum; F:AM 63193, calcaneum; F:AM 63194, calcaneum; and F:AM 63195, distal end of tibia.

Old Cabin Quarry, Quiburus Formation (late Hemphillian), near Redington, Pima County, Arizona: F:AM 72661, crushed skull with C–M2, left ramus with p2 and p4–m3 all broken, right humerus, astragalus; F:AM 72662, crushed partial skull with right C–P1 (broken), P2–M2, and left I2–P2, P3–P4 broken; F:AM 72663, left maxilla with P4– M2; F:AM 50685, right maxilla with P2–P4; F:AM 50686, left maxilla with P2–M2; F:AM 50688, right M1–M2; F:AM 75825*, crushed palate with C, P2–M2; F:AM 75836, crushed skull with P4 broken, left and right rami with c–m1, m2 broken, left and right humeri, metatarsals, astragalus and phalanx, scapula; F:AM 75796, skull with P4–M2; F:AM 75841, crushed skull with C–M2; F:AM 75838, skull with P2–M2; F:AM 75797, crushed skull with C, P2–M2; F:AM 75837, palate with P1–M2, right ramus with p2–p4 and m1–m2 both broken; F:AM 75843, palate with P3–M2; F:AM 75844, left maxilla with P3–M2; F:AM 75846, right maxilla with P4–M2; F:AM 75810, left and right rami with c–m3; F:AM 75811, left and right rami with c–m2; F:AM 75818, left ramus with p3–m3; F:AM 75845, right maxilla with P3–M2, left and right rami with p1–m3; F:AM 75799, left ramus with c–m2; F:AM 75806, left ramus with p4 broken–m3; F:AM 75807, right ramus with p1–m1; F:AM 75809*, c broken, p4–m2 all broken; F:AM 75812, left and right rami with m1–m2; F:AM 75813*, left ramus with p4 broken– m3; F:AM 75815, right ramus with p3–m3, left ramus with m1 broken–m2; F:AM 75816, left and right rami with p2 broken, p4 broken–m1; F:AM 75817, right m1; F:AM 72656 and 72656A, right and left rami with i3–m2 and m3 alveoli; F:AM 72657, left isolated m1; F:AM 50696, left isolated m1; F:AM 50697, right isolated m1; F:AM 72659, right isolated m1; F:AM 50695, right isolated m1; F:AM 72658, left ramal fragment with p4–m1; F:AM 75798, right partial ramus with c–m2; F:AM 50689*, left partial ramus with p1 alveolus p2–p3, p4 alveolus, m1–m2; F:AM 99373, partial skeleton including scapula, two humeri, two radii, one partial ulna exposed, metacarpals II–III, metatarsals II–V, two incomplete and broken metapodials, and articulate vertebrae; F:AM 73833B, right humerus; F:AM 75833C, left humerus; F:AM 75833D, right humerus, F:AM 75852, distal end right humerus, left tibia, astragalus, left metatarsals II–V; F:AM 75853, right tibia; F:AM 75834, left tibia, right radius, left ulna; F:AM 75849, articulated right metacarpals II–V; F:AM 75850, right metacarpals II–III; F:AM 75854, articulated metatarsals III–V; F:AM 75833, left humerus; F:AM 75833A, right humerus and fragments of radius and femur; F:AM 75833E, left humerus; F:AM 63209, right humerus.

Redington Quarry, Quiburus Formation (late Hemphillian), northwest of Redington, San Pedro River Valley, Pima County, Arizona: F:AM 63094, crushed skull with P2, P4–M2; F:AM 75840, fragmentary skull and rami, limbs, F:AM 75808*, crushed partial skull with broken teeth; F:AM 75804*, left ramus with c–p1, p4–m2, upper dentition with P2–P4 all broken and M1; F:AM 75835, crushed maxillae with C–P4 all broken, M1–M2, and partial ramus with i1– m2 all broken; F:AM 75839*, right maxilla with I1–M2; F:AM 63096, right partial maxilla with I1–M2; F:AM 75814*, left and right rami with c–m2; F:AM 63087, left ramus with p1–p2, m1; F:AM 63097*, right ramus with p2–p4 and m1 broken; F:AM 63086, isolated right M1, right ramus with m1; F:AM 63088, isolated right m1; F:AM 63088A*, right ramus with p2–p4; F: AM 63093*, right M1, left m2; F:AM 63095, right ramus with p4–m2; F:AM 62786*, right ramus with p2 broken–p4, m1 broken; F:AM 62789*, left ramus with p4; and F:AM 75851; left femur, left tibia, and calcaneum; and F:AM 108427, right humerus.

San Pedro Valley, Quiburus Formation (late Hemphillian), 13 miles south of Mammoth, San Pedro Valley, Pima County, Arizona: F:AM 63081, left partial maxilla with P3–M2, Hilltop Dig; F:AM 63084, left partial ramus with c–p1 and p3–m2 all broken, Least Camel Quarry, Camel Canyon; F:AM 63085*, left partial ramus with c–m1 all broken, Least Camel Quarry, Camel Canyon; F:AM 63090, right partial ramus with c–p4, m1 broken, Camel Canyon; and F:AM 63083*, right ramal fragment with p4 root–m1 broken.

Bidahochi Formation (late Hemphillian), Keams Canyon, Navajo County, Arizona: F:AM 23392, right partial ramus with m1 and m2–m3 alveoli.

Golgotha Water Mill Pothole locality (late Hemphillian), Spring Valley near Panaca, Lincoln County, Nevada: F:AM 49294, left (fig. 35R–S) and right rami with c–m2; F:AM 49291A, left ramus with m2; F:AM 49291A*, juvenile right ramus, deciduous premolars; F:AM 49293*, right ramus with all alveoli; F:AM 49296, right maxilla with P4, left ramus with p2–m2; F:AM 49297, right ramus with p3–m1; F:AM 62794, proximal end right ulna; F:AM 62794A, right metacarpal V; F:AM 62794B, left metacarpal III; F:AM 62794C, right metacarpal V; F:AM 62794D, left metacarpal IV; F:AM 62794E, right metacarpal IV; F:AM 62794F, calcaneum; F:AM 62794G, distal end of ulna; F:AM 62794H, phalanges; F:AM 62795, right isolated m1; F:AM 62795A, left isolated m1; F:AM 62795B*, right isolated p4; F:AM 62795C, isolated C; and F:AM 62795D, left isolated i3.

Turlock locality 4, UCMP locality V5837, Mehrten Formation (late Hemphillian), Stanislaus County, California: UCMP 52423, partial palate with P2–M2.

Pinole site 2, UCMP locality V3425, Pinole Formation (late Hemphillian), Alameda County, California: UCMP 62408, left partial ramus with p4 alveolus, m1–m2, m3 alveolus; UCMP 60667, left partial ramus with m1; UCMP 64836, left partial ramus with p2 broken, p3 alveolus–m2, m3 alveolus; and UCMP 58333, right ramus with c broken–p1 alveolus and p2–m2, m3 alveolus.

Fort Green Mine (Agrico), Polk County, Florida, Bone Valley Formation (late Hemphillian): UF 45884*, fragment of right ramus, m1–m2, m3 alveolus.

Yepomera (latest Hemphillian), Chihuahua, Mexico: LACM 30206*, isolated right broken M1, CIT locality 276; and LACM 30216*, right premaxilla and partial maxilla with I1–C alveoli, P1–P2, and P3 anterior root, CIT locality 287.

Distribution in North America: Early Hemphillian of Oregon and Nevada; late Hemphillian of Kansas, New Mexico, Oklahoma, Texas, Arizona, Nevada, Oregon, California, Florida, and northern Mexico.

Revised Diagnosis: Eucyon davisi differs from E.? skinneri in its larger size; longer jaw; more elongate, taller crowned premolars; p4 with second posterior cusp; m1 trigonid relatively longer, protoconid taller crowned, entoconid and hypoconid taller crowned, and larger hypoconulid shelf.

Eucyon davisi differs from Canis ferox and C. lepophagus in its smaller size and less robust skull and jaws; frontal sinus ends well before frontoparietal suture; jugal shallower relative to length of skull; width of skull across cheek teeth greater relative to length of skull; sagittal crest weaker; inion wider (never narrows to a point); premolars less robust; p4 anterolabial border generally less rounded; M1 paracone and metacone lower crowned and nearly subequal in size with stronger labial cingulum and stronger parastyle; m1 talonid without transverse crest between entoconid and hypoconid and hypoconulid shelf relatively smaller; angular process of mandible less expanded with smaller fossae for pterygoid muscle; and radius/tibia ratio less than 80%.

Description and Comparison: Numerous dentitions are referred to E. davisi , but a good skull representing the North American populations is still unknown. A brief description of the skull is herein based principally on three crushed skulls (F:AM 63010, 63007, and 63009, one of which (F: AM 63009) we have reconstructed (fig. 34I–K, P)) and a partial palate with an associated cranial fragment (F:AM 63005, fig. 34A–C) from the late Hemphillian Big Sandy Formation near Wikieup, Arizona. Chinese specimens of the species (Xiagou, Nihe subbasin, Gaozhuang Formation, early Pliocene, Yushe, Shanxi Province, Tedford and Qiu, 1996) are used to augment the comparisons where the North American evidence is inadequate.

The skull of E. davisi is intermediate in size to that of Vulpes vulpes and Canis latrans . Compared to C. lepophagus , the zygomae in E. davisi flare more laterally with a more marked eversion of the dorsal border. The frontals in E. davisi are narrower and less elevated, and the sinuses are less elongate and less posteriorly extended than in C. lepophagus . In the Chinese material (F: AM 97056), there is a dorsal inflation of the sinus behind the postorbital processes. Uninflated temporal crests join at or just anterior to the frontoparietal suture to form a low sagittal crest. The sagittal crest is weaker and the supraoccipital shield is narrower and more rounded and extends less posteriorly than in C. lepophagus . The basioccipital in E. davisi is narrow between the bullae, and the condyles are small. Compared to the size of the skull, the bullae average relatively and actually longer than those of C. lepophagus and the lip of the auditory meatus is smaller and less laterally extended. The upper incisors of E. davisi are simple, with only minute medial accessory cusps on I1 and I2, and a faint lingual cingulum is present on I1 and I2. The I3 is only slightly larger than I2 and lacks a medial accessory cusp, but it has a stronger lingual cingulum. The incisors are similar to those of Vulpes and relatively smaller than those of Canis . Although the premolars show considerable variation, they can be characterized as elongate, slender, and less robust than those of C. lepophagus . P3 is generally without a posterior cusp, but a minute cusp may occasionally be present. The morphology of the P4 varies in the Wickieup sample from the slender carnassial with a strong anterolingually directed protocone, a sharp anterolabial border and a deeply notched anterior border (F:AM 63058, fig. 35A) to a robust carnassial with a smaller and less anteriorly situated protocone, and a more rounded anterolabial border (F:AM 63056, fig. 35E). The former variant is predominant in the available E. davisi samples and these features are plesiomorphous. The latter variant is the dominant form of the P 4 in the C. lepophagus populations known to us. Both M1 and M 2 in E. davisi have a lowcrowned, nearly subequal paracone and metacone and a strong labial cingulum. M1 also has a prominent parastyle, a weak paraconule, and a strong protocone with a postprotocrista that joins the metaconule. A weak but distinct cingulum extends lingually from the base of the paracone across the base of the protocone and becomes continuous with the hypocone, ending at the metaconule. In most specimens the M1 is transversely narrow relative to its length as in the type of E. davisi . The M2 has a well-developed protocone and a greatly reduced metaconule, which may be limited to a low swelling at posterior extension of the postprotocrista. In some specimens the metaconule is absent as well as the postprotocrista. A distinct lingual cingulum extends from the paracone to the metaconule. Compared to C. lepophagus , the paracone and metacone are lower crowned and nearly subequal in size.

The horizontal ramus is shallower and less robust than that of C. lepophagus . Two mental foramina are present; the anterior foramen is below the p1 or below the diastema between p1 and p2. The smaller posterior foramen is below p3 with its position varying between the roots of this premolar. The deep masseteric fossa has a well-outlined anterior margin and most of the ventral margin is marked by a distinct masseteric crest. The angular process of the mandible is less expanded, and the fossa for the inferior pterygoid muscle is smaller than in Canis .

In E. davisi i1 is a simple peglike tooth. The i2 is slightly larger and has a small lateral accessory cusp. The i3 is still larger with a prominent lateral accessory cusp as in Vulpes and unlike the more robust incisors with stronger accessory cusps seen in Canis . The lower premolars are elongate and generally slender with the crown height varying from moderate to tall. A small posterior cusp is sometimes present on p2 (e.g., F:AM 63010, fig. 34G, O). The p3 posterior cusp varies from absent (e.g., F:AM 62932, fig. 33P–Q) to strong in F:AM 63010 (fig. 34G, O) and F:AM 63056 (fig. 35F–G) within a single population. Additionally, the p4 has a second posterior cusp in front of the cingulum. The tip of the major cusp of p4 lies at or above the paraconid of m1. The m1 trigonid in E. davisi varies from moderately short with a somewhat oblique paraconid (F:AM 23373, fig. 35H) to elongate with a less oblique shear (F: AM 63041). The protoconid is tall and a close examination will occasionally reveal a faint protostylid ridge. The hypoconid is larger than the entoconid and the two cusps are very rarely joined by a weak transverse crest (F:AM 63010, fig. 34O). On the first lower molar, the hypoconid and entoconid vary from being closely proximate at their bases (F:AM 63056, fig. 35F) to widely separated cusps (F:AM 23353, fig. 35H). The position of the entoconid is usually slightly posterior to that of the hypoconid, and a small entoconulid is sometimes present. Considerable variation is seen in the development of the hypoconulid. A small hypoconulid shelf is usually present (F:AM 63010, fig. 34O), but this varies to near absence (F:AM 63056, fig. 35F). In C. ferox the talonid is about as in E. davisi , but in C. lepophagus the m1 hypoconid and entoconid are usually joined by a transverse crest, and the hypoconulid shelf tends to be larger and a cusp is occasionally present.

The m 2 in E. davisi is usually larger, relative to the size of the m1, than that of C. lepophagus . A distinct paraconid is not present, but a strong crest (paracristid) extends anteriorly from the protoconid to the anterior cingulum. The well-developed anterolabial cingulum ends at the base of the protoconid. The metaconid is slightly smaller than the protoconid, with its position slightly posterior to the protoconid. The talonid is marked by a well-developed hypoconid, a small entoconid, and sometimes a small entoconulid. The m3 is a small tooth with an oval occlusal outline. It consists of two small cusps, the protoconid and metaconid. The protoconid is the larger and is situated slightly anterior to the metaconid. A weak crest runs anteriorly from the protoconid to the anterior border of the m3.

Based on the measurements of an articulated skeleton of E. davisi (F:AM 63010, fig. 36A–B and appendix 4) the length of the limb bones can be compared to those of Leptocyon , Vulpes , and Canis (fig. 52 and appendix 4). The relative proportions of the limb bones closely follow those of Leptocyon vafer (fig. 52). The presence of an occasional entepicondylar foramen of the humerus of Eucyon is a primitive feature relative to Canis . In Eucyon this foramen is usually absent, but when present, it is small relative to the size of the humerus with an extremely weak bridge enclosing the foramen. Unlike the limbs of Recent Canis species , the radius of E. davisi is short relative to the length of the humerus and tibia. The radius/tibia ratio of the articulated skeleton (F: AM 63010) is 78.7%, within the upper part of the range of such values for living Vulpes species. Additional primitive skeletal features of E. davisi , comparable to those of Vulpes , but unlike Canis , are a more robust ulna, a more erect olecranon process with a less concave anterior border, and a stronger posterior tuberosity (fig. 39C). Furthermore, the fibula of E. davisi also tends to be relatively stronger than that of its contemporary V. stenognathus . The tibia/femur ratio (F:AM 63010: 101.6%) in E. davisi approximates that in living species of Canis and is less than that in Vulpes . Metatarsal I in E. davisi is reduced to a short proximal rudiment, as in both recent Vulpes and Canis . Unfortunately, a comparison is impossible between the metatarsal I of E. davisi and V. stenognathus because it is unknown in the latter. However, an examination of the metatarsal II of V. stenognathus (F: AM 72580) shows that the articular facet for metatarsal I is relatively larger, and especially anteroposteriorly longer, than that of E. davisi and V. vulpes . This indicates that the proximal end of the metatarsal I of V. stenognathus was larger than that of E. davisi . Thus, the metatarsal I of V. stenognathus may have been intermediate in size between the functional digit I of Leptocyon and a proximal rudiment in V. vulpes . Such evidence also suggests that the metatarsal I of E. davisi may have been more reduced than that of its contemporary, V. stenognathus .

Discussion: Merriam (1906: 5) tentatively referred to the genus Canis a partial maxilla ( UCMP 545, fig. 33I) with M1–M2 apparently from the early Hemphillian Rattlesnake Formation of eastern Oregon. In 1911, he selected this maxilla as the type of C. davisi and referred additional teeth to that taxon from the early Hemphillian Thousand Creek Formation in northwestern Nevada. Merriam compared the type of C. davisi with the living coyotes of eastern Oregon and reported that the upper molars were a little smaller but the M2 was relatively larger and its metacone was about equal in size to the paracone. He described the M1 of C. davisi as having a laterally compressed and sharp paracone and metacone, with the protocone joining the incipient paraconule and metaconule to form a V-shaped ridge. We have found that these molars are also lower crowned, have stronger parastyles, and stronger labial cingula than the coyotes. These characters, and those noted by Merriam, serve to distinguish the upper molars of Eucyon davisi from those of Canis .

The type of Leptocyon shermanensis Hibbard, 1937 , is from the late Hemphillian, Edson Quarry, Kansas. According to Hibbard (1937), the length of the m 1 in the type is 17.3 mm and it lies within the size range of seven Edson specimens in our collection in which the m1 ranges from 17.0 to 18.0 mm in length. This sample differs markedly from both Leptocyon and Vulpes in its larger size, deeper horizontal ramus, especially beneath the p1, and more robust premolars. Moreover, the posterior cusps on p3 and p4 are stronger than in Vulpes . Regarding the broken m 1 in the type, Hibbard stated that the entoconid is weakly developed and there is no indication of a hypoconulid. We also note the lack of a transverse crest connecting the hypoconid and entoconid in Hibbard’s type. In the F:AM Edson sample the m1 entoconid varies from moderate to strong, and a weak transverse crest and a weak hypoconulid shelf are sometimes present. A partial palate (F:AM 49464, fig. 33J–K) in our topotypic sample is larger but morphologically similar to the type of E. davisi . The paracone and metacone are low-crowned, and the parastyle and labial cingulum are strong as in the type of E. davisi . A well- developed protocone in both M1 and M2 joins a strong metaconule in M1 and a greatly reduced metaconule in M2. Another specimen (F: AM 49456) having M2 lacks both the metaconule and postprotocrista. The morphology of the Edson sample is very similar to other late Hemphillian specimens herein referred to E. davisi .

Shotwell (1956: 733) described Canis condoni from the late Hemphillian McKay Reservoir Local Fauna in Northeastern Oregon and the type is a lower jaw with m2 ( UO F3241). His description of this taxon was also based on an isolated m1 fitting almost perfectly into the alveolus on the type jaw (fig. 33C–D). According to Shotwell’s diagnosis, the type m2 is transitional between that of Tomarctus and Canis in the presence of a small paraconid that is separated from the protoconid ‘‘by a minute valley.’’ We question the presence of a distinct paraconid and prefer to consider it the paracristid extending anteriorly from the protoconid. Hence, the morphology of the m2 is not really transitional but within the limits of variation in samples of E. davisi and species of Canis . The weak transverse crest between the entoconid and hypoconid and the small hypoconulid in the referred m1 are also characteristic of other samples of E. davisi and hence we refer C. condoni to that species.