Daphoenodon (Borocyon) niobrarensis Loomis, 1936

Robert M. Hunt, Jr., 2009, Long-Legged Pursuit Carnivorans (Amphicyonidae, Daphoeninae) From The Early Miocene Of North America, Bulletin of the American Museum of Natural History 2009 (318), pp. 1-95 : 21-23

Daphoenodon (Borocyon) niobrarensis Loomis, 1936 Figures 10 , 11 , 20 , 23

HOLOTYPE: ACM 3452 (field no. 34-52), left mandible with c, p2–m3, right mandible with c, p1–m3, and isolated right M1, associated with nearly complete forelimbs; holotype of Daphoenodon niobrarensis Loomis, 1936: 47 , figs. 2, 4. There is no doubt as to the identification of the holotype mandibles and forelimbs, which Loomis published as ACM 34-52 , although the field number 34- 58 appears on many of the individual bones.

HOLOTYPE HORIZON AND LOCALITY: From the lower Runningwater Fm., Cherry Co., Nebraska. Loomis (1936) reported that the holotype was ‘‘Found in 1934 in middle Miocene beds equivalent to the upper Harrison formation, near mouth of Antelope Creek, 12 miles southeast of Gordon, Nebraska. Associated with Aletomeryx [ ACM 1915].’’ In fact the holotype was found with a large sample of Aletomeryx and the camel Michenia [ ACM 1844] in Aletomeryx Quarry , an early Miocene locality in the lower Runningwater Fm. worked by several museums during the 1930s.

DIAGNOSIS: Borocyon species of intermediate size, with basilar skull length of, 270 mm, and c–m2 length of, 103– 115 mm, its skeletal and dental measurements (figs. 17, 18; tables 2, 3) generally falling between those of the large species B. robustum and small B. neomexicanus . Proximal tarsals (figs. 33, 34, astragalus, calcaneum) shorter and differently proportioned relative to those of B. robustum .

REFERRED SPECIMENS: Runningwater Formation, northwestern Nebraska — Cherry

Co., Nebraska: (1) ACM 11796 (field no. 34- 58), left metacarpals 3 and 4, Aletomeryx Quarry ; (2) F:AM 68269, right metatarsal 4, cuboid, navicular, phalanx, Aletomeryx Quarry. Dawes Co. , Nebraska: (1) UNSM 25683 (field no. 1-11-9-36NP), left mandible, p4–m2; (2) UNSM 25555 (field no. 1-13-8- 36NP), left humerus; (3) UNSM 44702 (field no. 9-12-8-36NP), right metacarpals 2, 3, and 4, possibly the same individual as UNSM 25555 and 25683. All from Red Horse Quarry (UNSM Dw-103). Sheridan Co., Nebraska: (1) UNSM 26418 (no field no.), right m2, UNSM Loc. Sh-101B. Sioux Co., Nebraska: (1) F:AM 107601 (F:AM field nos. NEA 1–2, 8–130; UNSM field no.

RH104), right mandible with c, p1–m3, partial right scapula, left ulna, left scapholunar, left metacarpal 2, right innominate, right calcaneum, astragalus, and cuboid, proximal metatarsal 5, proximal phalanx, intermediate phalanx, partial proximal phalanx. F:AM 107601 is an associated partial skeleton from a massive pinkish silty sandstone in SW1/4, SW1/4, sec. 1, T29N, R55W, northeast of the post office of Agate, Nebraska. F:AM specimens were collected by Ron Brown in August 1970; UNSM material (metacarpal 2, ulna, calcaneum, partial scapula) was collect- ed in July 1971 by R.M. Hunt, T. Hussain, and L. Hunt and donated to the American Museum. Associated with Merycochoerus cf. M. magnus . (2) UNSM 44827, nearly complete skull and mandibles but lacking much of the rostrum; teeth extremely worn; right P3–M2, left M1–M3, partial P4; damaged right p4–m3 and left m1–m3; from massive pale reddish brown sandstone, Skavdahl Ranch, NW1/4, NW1/4, sec. 29, T29N, R 53W.

REFERRED SPECIMENS: Late early Miocene beds east of the Laramie Mountains, southeastern Wyoming ( Cassiliano, 1980: 30– 39)— Laramie Co., Wyoming: (1) UW 10004, left mandible with p4–m2 (a right mandible was retained by the field collector and is now lost), left M3, left P3, left canine, left scapula, humerus, ulna, and radius, right humerus and ulna, two right radii, right magnum, both pisiforms, left metacarpals 4 and 5, right innominate, left femur, tibia, and fibula, right astragalus and calcaneum, left navicular, right metatarsal 2, left metatarsals 3 and 4, four proximal phalanges, axis, two cervical vertebrae, three thoracic vertebrae, two lumbar vertebrae, one caudal vertebra, partial ribs. From the ‘‘Middle Miocene Formation’’ of Cassiliano (1980) at Horse Creek Quarry.

REFERRED SPECIMEN: Carpenter Ranch Formation, southeastern Wyoming ( Hunt, 2005)— Goshen Co., Wyoming: (1) UNSM 44815, partial left mandible with m1–m3, partial p4, described in Hunt (2005: 32, fig. 22). From indurated sandstone caprock at Merycochoerus Butte.

Figures

Fig. 10. Holotype right mandible of Borocyon niobrarensis Loomis with c, p1–p4, and m1–m3 from Aletomeryx Quarry, lower Runningwater Fm., Cherry Co., Nebraska (ACM 3452).

Fig. 11. Associated holotype right forelimb of Borocyon niobrarensis Loomis (ACM 3452), Aletomeryx Quarry, Cherry Co., Nebraska.

Fig. 20. Comparison of the scapulae of (A) Borocyon niobrarensis (ACM 3452); (B) Ursus americanus

Fig. 23. Comparison of the ulnae of Amphicyon galushai (left) and Borocyon niobrarensis (center and right), showing the more elongate, slender, curved ulna of the latter species. No complete ulna of B. robustum is known; however, eight radii of this species demonstrate the existence of an even more slender, elongate ulna.