Daphoenodon (Borocyon) Peterson, 1910

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 : 14-21

Daphoenodon (Borocyon) Peterson, 1910

Borocyon robustum Peterson, 1910 .

DIAGNOSIS: The subgenus Borocyon differs from all other New World amphicyonids by its longer distal forelimbs and by proportions of the proximal tarsals (figs. 33, 34). Borocyon differs from its sister subgenus Daphoenodon by its longer distal forelimbs and by a ‘‘folded’’ M2, as well as by measurements of the dentition (figs. 17, 18; tables 2, 3). It is distinguished from Amphicyon galushai by its unreduced premolars, more sectorial carnassials, reduction and loss of M3, ‘‘folded’’ occlusal surface of M2, differently proportioned proximal tarsals (figs. 33, 34), and longer distal forelimbs with much more elongate paraxonic metapodials (see text for discussion of postcranial anatomy).

ETYMOLOGY: From the Greek boRóz, ‘‘devouring’’, and KÚvn,‘‘dog’’.

On the reduction of the genus Borocyon Peterson, 1910 , to the rank of subgenus:

International Code of Zoological Nomenclature (1985): Article 43— (a) A name established for a taxon at either rank in the genus group [i.e., genus or subgenus] is deemed to be simultaneously established with the same author and date for a taxon based upon the same name-bearing type (type species) at the other rank in the group, whether that type was fixed originally or subsequently. (b) When a nominal taxon is raised or lowered in rank in the genus group its type species remains the same [the neuter -um is retained here although robustus is appropriate].

Daphoenodon (Borocyon) robustum Peterson, 1910 Figures 3–8 , 15 , 21 , 22 , 24–28 , 31 , 32 , 37–39

Borocyon robustum Peterson, 1910 .

Large daphoenine, n. sp., Hunt and Stepleton, 2004: 87, 89.

HOLOTYPE: CM 1918 (field no. 2905), right mandibular fragment with c, p2, an isolated m2 (not reported by Peterson), three complete and one partial caudal vertebrae, a right astragalus, navicular, ecto-, ento-, and mesocuneiforms, 11 phalanges, a trapezoid, sesamoid, five fragmentary metapodials [left proximal metatarsal 3, proximal and?distal metacarpal 5, two metapodial diaphyses without proximal or distal ends, complete right metacarpal 1], distal tibia, shaft and distal end of fibula (fig. 3).

HOLOTYPE HORIZON AND LOCALITY: From the Runningwater Fm., Sioux Co., Nebraska. The original field label states: upper Loup Fork (Nebraska beds), 5 miles east of Agate , 3 miles south of the Niobrara River , Sioux Co. , Nebraska. Collected by T. F. Olcott, 13 October 1905. Peterson (1910: 263) reported the horizon as ‘‘ Upper Harrison beds’’ and the locality as ‘‘ Whistle Creek , Sioux County , Nebraska’ ’.

DIAGNOSIS: Largest known daphoenine amphicyonid, and the largest species of Borocyon , with basilar skull length of 285– 294 mm, differing from B. niobrarensis by larger average body size and dentition (c–m2 length,, 110–120 mm), consistent loss of M3, more elongate forelimbs, and greater modification of proximal tarsals (figs. 33, 34, astragalus-calcaneum) for fore–aft motion (see text for detailed discussion). Distinguished from B. neomexicanus by much larger body size, dentition (figs. 17, 18; tables 2, 3), and more elongate yet anatomically similar distal forelimbs.

PARATYPES: UNSM 25686 (field no. 2-6- 8-35 NWP), skull lacking basicranium, with right P3, M1–2, left P2–M2 ; UNSM 25685 (field no. 3-6-8-35 NWP), right mandible, p2, p4–m3. The mandible was found in proximity to the skull ; the skull and mandible probably represent a single individual.

PARATYPE HORIZON AND LOCALITY: Runningwater Formation (upper part), Marsland Quarry (UNSM Loc. Bx-22), Box Butte Co., Nebraska.

REFERRED SPECIMENS: Runningwater Formation, northwestern Nebraska —

SKULLS, MANDIBLES, AND ISOLATED TEETH

Box Butte Co., Nebraska: (1) UNSM 25547 (field no. 2499-39), skull with right P2, P4–M2, left P4, Hemingford Quarry 7B; (2) UNSM 26416 (field no. 4553-41), skull

lacking posterior cranium, with right P4–M2, left P2, P4–M2, Hemingford Quarry 12D; (3) UNSM 25548 (field no. 2200-39), right mandible, c, p1–m3, Hemingford Quarry 7B; (4) UNSM 25549 (field no. 1000-39), right man- dible, i2–i3, p1–m3, Hemingford Quarry 7B; (5) UNSM 25550 (field no. 2201-39), right mandible, p2–m3, Hemingford Quarry 7B; (6) UNSM 25551 (field no. 4946-40), right mandible, p4–m2, Hemingford Quarry 12D; (7) UNSM 25552 (field no. 73-9-8-37NP), juvenile right mandible, dp4, m1–m3 erupting, Hemingford Quarry 12D; (8) UNSM 25684 (field no. 181-7-8-37SP), left mandible, c, p1–m3, Hemingford Quarry 7A; (9) UNSM 25577 (field no. 4941-40, right mandibular fragment, p2–p4, Hemingford Quarry 12D; (10) UNSM 27002 (field no. 4675- 40), left mandible, c, p2–m2, Hemingford Quarry 12D; (11) UNSM 26417 (field no. 5549-68), right mandible, i2–i3, c, p2– m3, Hemingford Quarry 21 (Hovorka’s Quarry); (12) FA:M field no. H457-4060, left mandible, p4–m2, Hemingford Quarry 1 (Barbour-Hemingford Quarry); (13) UNSM 25576 (field no. 1701-39), mandibular fragment, p3 and partial p4, Hemingford Quarry 7B. Dawes Co., Nebraska: (14) F:AM 25408, left mandible, m1–m2, damaged p3–p4, Dunlap Camel Quarry. Dawes Co., Nebraska: (15) F:AM 25402, left P4; (16) F:AM 25403, left P4; (17) F:AM 25404, left M2; all from Dunlap Camel Quarry. Box Butte Co., Nebraska: (18) UNSM 25571 (field no. 2207-39), right m1, Hemingford Quarry 7B; (19) UNSM 26422 (field no. 19-29-7- 35NWP), right m1, heavily worn, Hemingford Quarry 23 (Shimek’s Quarry); (20) UNSM 26423 (field no. 1018-39), left p4, Hemingford Quarry 7B; (21) UNSM 26452 (field no. 2004-39), right P4; (22) UNSM 26427 (field no. 5-12-8-37SP), right M2, Hemingford Quarry 12A.

POSTCRANIALS—FORELIMB

Box Butte Co., Nebraska: (1) UNSM 26419 (34-26-6-35NWP), diaphysis of right humerus, Hemingford Quarry 23 (Shimek’s

Quarry); (2) UNSM 26420 (field no. 4863- 41), distal left humerus, Hemingford Quarry 12D; (3) UNSM 26421 (field nos. 1 to 3-17-7- 37NP), distal left humerus, proximal radius, proximal ulna, Hemingford Quarry 12D; (4) UNSM 25554 (field no. 5500-38), distal left humerus, left proximal ulna, left radius, proximal left MC2 and left MC3, a distal metapodial, and numerous fragments,,0.25 mi west of Hemingford Quarry 1; (5) UNSM 26424 (field no. 39-7-8-37SP), proximal right ulna, Hemingford Quarry 7B; (6) UNSM 25553 (field no. 179-7-8-37SP), left radius, Hemingford Quarry 7B?; (7) UNSM 25595 (field no. 73-4-8-37NP), right radius, Hemingford Quarry 12D; (8) UNSM 26425 (field no. 4025-40), right radius, Hemingford Quarry 7A; (9) UNSM 26426 (field no. 4612-41), right radius, Hemingford Quarry 12D; (10) UNSM 26428 (field no. 171-39), right scapholunar, Hemingford Quarry 12D; (11) UNSM 26429 (field no. 334-13-8-38NP), right scapholunar, Hemingford Quarry 12D; (12) UNSM 26430 (field no. 2636-40), right scapholunar, Hemingford Quarry 7B; (13) UNSM 26431 (field no. 12-24-6-35NWP), right scapholunar, Marsland Quarry (Bx-22).

METACARPALS (MC1 is not represented): (14) UNSM 25574 (field no. 24,281-39), left metacarpal 2, Hemingford Quarry 7B; (15) UNSM 26432 (field no. 4395-41), left MC2, Hemingford Quarry 12D; (16) UNSM 25564 (field no. 35-7-8-37SP), right metacarpal 3, Hemingford Quarry 7B; (17) UNSM 26433 (field no. 145-27-10-37), right metacarpal 3, Hemingford Quarry 12D; (18) UNSM 26434 (field no. 3-4-6-35NWP), right metacarpal 3, Marsland Quarry (Bx-22); (19) UNSM 25572 (field no. 347-39), left metacarpal 5, Hem-

ingford Quarry 12D. Dawes Co., Nebraska: (20) F:AM 68263, right metacarpal 4, Dunlap Camel Quarry.

POSTCRANIALS—HINDLIMB

Box Butte Co., Nebraska: (1) UNSM 26435 (field no. 4-15-7-35NWP), left femur, Hemingford Quarry 23 (Shimek’s Quarry); (2) UNSM 25558 (field no. 1639-39), right tibia, Hemingford Quarry 7B; (3) UNSM 44720 (field no. 53-13-8-38NP), left ectocuneiform, Hemingford Quarry 12D; (4) UNSM 26436 (field no. 1565-39), left astragalus, Hemingford Quarry 7B; (5) UNSM 25585 (field no. 73-39), left astragalus, Hemingford Quarry 12D; (6) UNSM 25562 (field no. 1898-39), right astragalus, right distal calcaneum, right cuboid, Hemingford Quarry 7B (see associated metatarsals); (7) UNSM 26437 (field no. 9-12-8-37SP), left astragalus, Hemingford Quarry 12A; (8) UNSM 25584 (field no. 73-39), left calcaneum, Hemingford Quarry 12D; (9) UNSM 26438 (field no. 4929-41), left calcaneum, Hemingford Quarry 12D; (10) UNSM 26439 (field no. 4929- 41), right calcaneum, Hemingford Quarry 12D; (11) UNSM 25586 (field no. 13-11-7- 35NWP), right calcaneum, Hemingford Quarry 23 (Shimek’s Quarry); (12) UNSM 48478 (field no. 2588-40), left calcaneum, Hemingford Quarry 7B; (13) UNSM 26440 (field no. 389-39), right calcaneum, Hemingford Quarry 12D; (14) UNSM 26441 (field no. 7-6-8-37SP), left calcaneum, Hemingford Quarry 6; (15) UNSM 26442 (field no. 5-20- 6-35NWP), right cuboid, Marsland Quarry (Bx-22); (16) UNSM 26497 (field no. 40-2-10- 37NP), right cuboid, Hemingford Quarry 12D.

METATARSALS (MT1 is not represented): (17) UNSM 26443 (field no. 325-13-8-38NP), left MT2, Hemingford Quarry 12D; (18) UNSM 26444 (field no. 2-4-6-35NWP), right metatarsal 2, Marsland Quarry (Bx-22); (19) UNSM 26445 (field no. 5091-40), left metatarsal 3, Hemingford Quarry 12D; (20) UNSM 26446 (field no. 14-3-8-35NWP), right metatarsal 3, Marsland Quarry (Bx-22); (21) UNSM 25562 (field no. 1898-39), right metatarsal 3 and proximal metatarsal 4, Hemingford Quarry 7B; (22) UNSM 25563 (field no. 14-13-8-38NP), left metatarsal 4, Hemingford Quarry 12D; (23) UNSM 26447 (field no. 4611-40), right metatarsal 4, Hemingford Quarry 7B; (24) UNSM 26448 (211-13-8- 38NP), right metatarsal 4, Hemingford Quarry 12D; (25) UNSM 26449 (field no. 4517-41), right metatarsal 5, Hemingford Quarry 12D; (26) UNSM 26450 (field no. 2-3-8-35NWP), right metatarsal 5, Marsland Quarry (Bx-22).

Dawes Co., Nebraska: All from Dunlap Camel Quarry: (27) F:AM 68265B (field no. H198-2392), right astragalus; (28) F:AM field no. H173-1509, left calcaneum; (29) F:AM field no. H275-2716, right metatarsal 4; (30) F:AM 68265A, metatarsal 5.

REFERRED SPECIMENS: Bridgeport Quarries, Unnamed formation, western Nebraska —if a particular quarry is not indicat- ed, then the general designation for all quarries applies:

MANDIBLES AND ISOLATED TEETH

Morrill Co., Nebraska: (1) UNSM 25878 (field no. 20-7-32SPD), partial mandible with i2–i3, c, p1–p4; (2) UNSM 25852 (field no. 11537-40), mandible with damaged p4– m2, alveoli for p1–p3, m3; (3) UNSM 26070 (67-SPD-32), right P4; (4) UNSM 26071 (field no. SPD), left P4; (5) UNSM 25961 (field no. 13-20-10-32SPD), right P4; (6) UNSM 26451 (field no.?), right P4; (7) UNSM 26017 (field no. 53-SPD-3), right M1; (8) UNSM 26015 (field no. 43-SPD- 32), right M1; (9) UNSM 25928 (field no. 16- 28-10-33NSM), right M1; (10) UNSM 26016 (field no. 8NSM), left M1; (11) UNSM 26072 (field no. SPD), left M1; (12) UNSM 26018 (field no. 81-SPD-32), left M2; (13) UNSM 26019 (field no. NSM), left M2; (14) UNSM 26009 (field no. 22-SPD-32), left p3; (15) UNSM 25924 (field no. 13-20-10-32SPD), left p4; (16) UNSM 26011 (field no. SPD), right p4; (17) UNSM 25923 (field no. 13-20- 10-32SPD), right p4; (18) UNSM 26012 (field no. 15-SPD-32), left p4; (19) UNSM 25781 (field no. 6-SPD-32), right m1; (20) UNSM 25907 (field no. 16-28-10-33NSM), left m1; (21) UNSM 26080 (field no. SPD), right m1; (22) UNSM 26082 (field no. 2-SPD-32), right m1; (23) UNSM 26083 (field no. 8-SPD-32), right m1; (24) UNSM 26084 (field no. 26- SPD-32), left m1; (25) UNSM 26281 (field no. SPD-13-10-20-32), right m2; (26) UNSM 26282 (field no. SPD-13-10-20-32), left m2; (27) UNSM 26283 (field no.?9-8-32SPD), right m2; (28) UNSM 26284 (field no.?9-9- 32SPD), right m2; (29) UNSM 26287 (field no.?9-8-32SPD), left m2 trigonid.

POSTCRANIALS—FORELIMB

Morrill Co., Nebraska: (1) UNSM 26260 (12-17-10-33NSM), right humerus, Mo-114; (2) UNSM 26261 (14-28-10-33NSM), left humerus lacking proximal end; (3) UNSM 26262 (field no. SPD-B-7-20-32), left distal humerus; (4) UNSM 26263 (SPD-B-7-20-32), left distal humerus; (5) UNSM 26264 (field no. 14-28-10-33NSM), right distal humerus; (6) UNSM 26265 (field no. 11-17-10- 33NSM), left distal humerus; (7) UNSM 26266 (field no. 11-17-10-33NSM), right distal humerus; (8) UNSM 26267 (field no. 11- 17-10-33NSM), left distal humerus; (9) UNSM 26268 (field no. 14-28-10-33NSM), left distal humerus; (10) UNSM 26269 (field no. 10405-40), left distal humerus, Loc. A, Qu. 1; (11) UNSM 26270 (field no. SPD-4- 10-20-32), right distal humerus; (12) UNSM 26218 (field no. 4-10-20-32-SPD), right distal humerus; (13) UNSM 26210 (field no. 17-27- 9-33NSM), left distal humerus; (14) UNSM 26297 (field no. 14-17-10-33NSM), right radius, Mo-114; (15) UNSM 25877 (field no. 10694-40), left radius, Loc. A, Qu. 1; (16) UNSM 26453 (field no. 27-9-11- 32NSM), left scapholunar; (17) UNSM 26454 (field no. 2-7-37-SPA), right scapholunar, Qu. 4; (18) UNSM 26455 (field no. 1-9- 32SP), right scapholunar, Qu. 2; (19) UNSM 26456 (field no. 14106-40), left scapholunar, Qu. 1; (20) UNSM 26457 (field no. 1-9- 32SP), left unciform, Qu. 2; (21) UNSM 26458 (field no. 1-9-32SP), left unciform, Qu. 2; (22) UNSM 26459 (field no. 11394-40), Qu. 1.

METACARPALS: (23) UNSM 26460 (field no. 10-10-32-SPD), left metacarpal 1; (24) UNSM 26461 (field no. SPD), right metacarpal 1; (25) UNSM 26462 (field no. NSM 26), left metacarpal 2; (26) UNSM 26463 (field no. 4-28-10-33NSM), left metacarpal 2; (27) UNSM 26464 (field no. 10-10-20-32- SPD), right metacarpal 2; (28) UNSM 26465 (field no. 29-17-10-33NSM), right metacarpal 2; (29) UNSM 26466 (field no. NSM 6), right metacarpal 2; (30) UNSM 26467 (field no. 10719-40), left metacarpal 3; (31) UNSM 26468 (field no. 5-27-9-33NSM), left metacarpal 3; (32) UNSM 26469 (field no. SPD), right metacarpal 3; (33) UNSM 26470 (field no. 10495-40), right metacarpal 3, Loc. A, Qu. 1; (34) UNSM 26471 (field no. 29-17-10-33NSM), right metacarpal 3; (35) UNSM 26472 (field no. 10-10-20-32- SPD), right metacarpal 3; (36) UNSM 26473 (field no. 10164-40), left metacarpal 4, Qu. 1; (37) UNSM 26474 (field no. 29-17- 10-33NSM), right metacarpal 4; (38) UNSM 26475 (field no. 10-10-20-32-SPD), right metacarpal 4; (39) UNSM 26476 (field no. 10164-40), right metacarpal 4 (pathologic), Qu. 1; (40) UNSM 26477 (field no. 25-6- 34SP), left metacarpal 5; (41) UNSM 26478 (field no. NSM 6), left metacarpal 5; (42) UNSM 26479 (field no. NSM 6), right metacarpal 5; (43) UNSM 26480 (field no. 10-10-20-32-SPD), right metacarpal 5.

POSTCRANIALS—HINDLIMB

Morrill Co., Nebraska: (1) UNSM 26343 (field no. 10-4-10-33NSM), left femur; (2) UNSM 26360 (field no. 18-17-10-33NSM), right tibia, Qu. 2, Mo-114; (3) UNSM 26361 (field no. 8-7-8-34SP), right proximal tibia, Qu. 8; (4) UNSM 26481 (field no. 7514-83), left calcaneum; (5) UNSM 26482 (field no. 28-17-10-33NSM), right calcaneum; (6) UNSM 26483 (field no. 1-9-32-SP), right calcaneum, Qu. 2; (7) UNSM 26484 (field no. 1-9-32-SP), left calcaneum, Qu. 2; (8) UNSM 26485 (field no. 27-9-33NSM), right calcaneum, Qu. 2; (9) UNSM 26486 (field no. 27-9-33NSM), left calcaneum, Qu. 2; (10) UNSM 26496 (field no.?), left calcaneum; (11) UNSM 26487 (field no. 1-9-32-SP), left astragalus, Qu. 2; (12) UNSM 26488 (field no. 10125-40), left astragalus, Qu. 1; (13) UNSM 26489 (field no. 27-9-33NSM), left astragalus, Qu. 2; (14) UNSM 26490 (field no. 27-9-33-NSM), left astragalus, Qu. 2; (15) UNSM 26491 (field no. 11-10-20-32- SPD), right astragalus; (16) UNSM 26492 (field no. 8-28-10-33NSM), right astragalus; (17) UNSM 26493 (field no. 1-17-7-35-SP), right astragalus, Qu. 5; (18) UNSM 26494 (field no. 11-10-20-32-SPD), right astragalus; (19) UNSM 26495 (field no. 6-27-9-33NSM), right astragalus; (20) UNSM 26498 (field no. 6-7-34SP), right cuboid, Qu. 1; (21) UNSM 26499 (field no. 11156-40), left cuboid, Qu. 10; (22) UNSM 26405 (field no. 27- 9-33NSM), left cuboid, Qu. 2; (23) UNSM 26406 (field no. 27-9-33NSM), right navicular, Qu. 2; (24) UNSM 26407 (field no. 11005- 40), left navicular, Qu. 10; (25) UNSM 44703 (field no. SPD-12-10-20-32), right calcaneum; (26) UNSM 44704 (field no. SPD-12-10-20- 32), right calcaneum; (27) UNSM 44706 (field no. SPD-12-10-20-32), right calcaneum; (28) UNSM 44707 (field no. SPD-12-10-20-32), right calcaneum; (29) UNSM 44708 (field no. SPD-12-10-20-32), left calcaneum.

METATARSALS: (30) UNSM 26408 (field no. SPD), right metatarsal 2; (31) UNSM 26409 (field no. NSM), left metatarsal 2; (32) UNSM 26410 (field no. 10164-40), left metatarsal 2, Qu. 1; (33) UNSM 26411 (field no. 29-17-10-33NSM), right metatarsal 3; (34) UNSM 26412 (field no. 10-10-20-32- SPD, right metatarsal 3; (35) UNSM 26413 (field no. 4-4-10-33NSM), left metatarsal 3; (36) UNSM 26414 (field no. 29-17-10- 33NSM), right metatarsal 4; (37) UNSM 44700 (field no. 10-10-20-32-SPD), left metatarsal 5; (38) UNSM 44701 (field no. 10-10- 20-32-SPD), right metatarsal 5.

REFERRED SPECIMENS: From sediments yielding an early Hemingfordian mammal fauna from the Rose Creek Member, John Day Formation, north-central Oregon — Grant Co., Oregon: (1) UCMP 76875, left p2–m2 (UCMP locality V76124 ); (2) UNSM 8061-93, right upper canine, right m2, left I3, right and left I2 (UCMP locality V76124 ), possibly from the same individual as UCMP 76875; (3) UNSM 7088-94, lingual fragment of M1 (UNSM locality Rose Creek North), tentatively referred; (4) UCMP 76864, right astragalus (UCMP locality V76124 ).

REFERRED SPECIMENS: From sediments yielding an early Hemingfordian mammal fauna, Zia Sand Fm., Chamisa Mesa Member— Sandoval Co., New Mexico: (1) F:AM 68254 (field no. Jemez 31-504), left metacarpals 4 and 5, Blick Quarry.

Figures

Fig. 3. Peterson’s holotype of Borocyon robustum (CM 1918): an anterior mandible with right p2, p1 alveolus, and worn canine; two caudal vertebrae indicating a long tail; distal right tibia and fibula; partial right tarsus-metatarsus including astragalus, navicular, ecto-, meso-, and entocuneiforms, and parts of metatarsals 3, 4, and 5. Runningwater Fm., Whistle Creek area, Sioux Co., Nebraska.

Fig. 4. Cranium of Borocyon robustum (UNSM 26416), Hemingford Quarry 12D, Box Butte Co., Nebraska, upper Runningwater Fm., early Hemingfordian. A, Dorsal view showing broad forehead for expanded frontal sinuses; B, ventral view showing broad palate, P4–M2, and characteristic absence of M3 in B. robustum.

Fig. 5. Stereoimage of the diagnostic upper molars (M1–M2) and carnassial (P4) of Borocyon robustum (UNSM 25547), Hemingford Quarry 7B, upper Runningwater Fm., Box Butte Co., Nebraska. Note elongate P4, the notch (at arrow) in the anterolingual cingulum of M1, the ‘‘folded’’ M2 (see text), and absence of M3.

Fig. 6. Mandible of Borocyon robustum (UNSM 25548), Hemingford Quarry 7B, Box Butte Co., Nebraska, upper Runningwater Fm., early Hemingfordian. A, Lateral view, right c, p1–p4, m1–m3; B, medial view. Note m3 elevated on margin of ascending ramus.

Fig. 7. Comparison of dentitions of Borocyon robustum (A, B) and B. neomexicanus (C–E), end member species of the Borocyon lineage. A, UNSM 25547, P2, P4–M2, alveoli for C, P1, P3; B, UNSM 25684, c, p1–p4, m1–m3; C, F:AM 49241, juvenile, p2, p4–m3; D, F:AM 49239, P1–P4, M1–M3; E, F:AM 49239, c, p1–p4, m1, m3, alveoli of m2.

Fig. 8. Occlusal views of p4–m3 of the end-member species of the Borocyon lineage. A, B. robustum, UNSM 25552; B, B. neomexicanus, F:AM 49241. The squared posterior border of p4 is characteristic of species of the subgenera Borocyon and Daphoenodon.

Fig. 15. Elongate metacarpals 4 and 5 of (A) Borocyon neomexicanus (F:AM 68242) from Standing Rock Quarry and (B) B. robustum (F:AM 68254) from Blick Quarry, Sandoval Co., New Mexico, demonstrating that the Borocyon lineage persisted in the southwestern United States from latest Arikareean into the early Hemingfordian. The only Hemingfordian record of Borocyon in the Southwest are these two metacarpals from Blick Quarry.

Fig. 21. Comparison of the distal humerus of Borocyon robustum (right, UNSM 26420) and Amphicyon galushai (left, UNSM 26375). The narrow distal humerus and symmetric olecranon fossa of B. robustum parallel the form of the distal humerus of the wolf and cheetah, indicating parasagittal orientation of the forelimb with minimal elbow eversion.

Fig. 22. Elongate radii of Borocyon robustum and the cheetah Acinonyx jubatus compared to the short, robust radius of Amphicyon galushai. A slender, elongate radius with flattened blade-like shaft and transversely narrow proximal and distal ends characterizes both B. robustum and the cheetah. Left, Acinonyx; center, B. robustum; right, A. galushai.

Fig. 24. Comparison of the carpus (anterior view) of Borocyon robustum and those of Panthera leo, Canis lupus, and Ursus arctos. See text for discussion. 1, Elevated bony ridge on scapholunar forcing ulnar deviation of the forepaw during flexion of the wrist; 2, scapholunar process inserted in concavity of magnum preventing hyperextension within the carpus (this stop mechanism is maximally developed in the cheetah). Abbreviations: a, scapholunar; b, carpal cuneiform; c, unciform; d, magnum; e, trapezoid; f, trapezium.

Fig. 25. Comparison of the carpus (plantar view) of Borocyon robustum and those of Panthera leo, Canis lupus, and Ursus arctos. See text for discussion. Gray tone indicates extent of articular surfaces for scapholunar on magnum and unciform; in ursid and B. robustum the scapholunar moves largely unimpeded over these surfaces during intracarpal flexion but in lion and wolf there is a bony stop (3) between unciform and scapholunar that arrests this movement (this stop is even more developed in the cheetah). Abbreviations as in figure 24: vp, volar process.

Fig. 26. Restoration of the Borocyon robustum forefoot illustrating the interosseous muscle supporting each paraxonic metacarpal-phalangeal joint, the short middle phalanges, elongate unguals, and presumed dense fibrous metacarpal and digital pads.

Fig. 27. Placement of the fovea capitis femoris for the femoral ligament in Borocyon robustum and some living carnivorans. In cheetah, puma, and wolf the fovea is more centrally situated on the femoral head, whereas in the lion, tiger, and B. robustum it is more posteriorly placed, indicating a somewhat more abducted femur in these large felids and Borocyon. Diagram of articulated femur and pelvis shows femoral head of B. robustum fully adducted; the femur is more abducted in normal stance. A, Acinonyx jubatus; B, Canis lupus; C, Felis concolor; D, Panthera leo; E, Borocyon robustum; F, Panthera tigris.

Fig. 28. Tibia of Borocyon robustum (UNSM 25558) compared with the tibia of the cheetah Acinonyx jubatus (ZM 16913) showing a similarity in form. The sulcus muscularis (sm), a groove for the long digital extensor muscle of cheetah and wolf is absent in B. robustum, but the extended cnemial crest and developed tibial tuberosity are shared traits.

Fig. 31. Comparison of the astragalus of Borocyon robustum (A, B) and Amphicyon galushai (C, D). Dimorphic astragali within each species are thought to represent large males (B, D) and smaller females (A, C).

Fig. 32. Comparison of calcanea of Amphicyon galushai (A) and Borocyon robustum (B, male; C, female). Digitigrade calcanea of B. robustum are more slender and distally narrower than Amphicyon calcanea. Cuboids of A. galushai (D, F) and B. robustum (E, G), anterior and medial views: a, calcaneal articular surface; b, ectocuneiform and c, navicular facets.

Fig. 37. Hypothetical restoration of the skeleton of Borocyon robustum (A) compared to the holotype skeleton of Daphoenodon superbus (B, from Peterson, 1910), representing the two end-member species of the Borocyon lineage during the early Miocene in North America. Fossils show that Borocyon robustum, the terminal species of the subgenus, was widely distributed from the Pacific Northwest to the Gulf Coast of Florida by the end of the early Hemingfordian.

Fig. 38. Mandibular symphyses of (A) Borocyon robustum, (B) Ursus americanus, and (C) Canis lupus, in medial view, showing the symphyseal plate. Dashed line encloses the smooth bone for attachment of the subrectangular fibrocartilage pad (fc) in the wolf, which is inferred for Borocyon robustum. The symphyses of Borocyon and the wolf are considered to be flexible. The rugose, bony interdigitations of B. robustum symphyseal

Fig. 39. Mandibular force profiles of large living carnivorans and the amphicyonid Borocyon robustum