Temnocyon fingeruti, Hunt, 2011

Hunt, Robert M., 2011, Evolution Of Large Carnivores During The Mid-Cenozoic Of North America: The Temnocyonine Radiation (Mammalia, Amphicyonidae), Bulletin of the American Museum of Natural History 2011 (358), pp. 1-153 : 45-50

Temnocyon fingeruti , new species Figures 16–19 , 68

TYPE: NM 280/61, a complete skull and lower jaws in articulation, the rostrum offset, 3 cm from the posterior cranium by sediment deformation after burial; both left and right I1–3, C, P1–4, M1–2 and left i3, c, p2–4, m1–3, right c, p1–4, m1–3, from the Haystack Valley Member (revised), John Day Formation , Oregon, Lower Beardog Section , E 1/2, NE4, SW4, SW4, sec. 27, T8S, R25E, Kimberly 7.5-minute quadrangle, from 96 ft stratigraphic level in appendix 1–6, Hunt and Stepleton (2004: 81) ; 62 ft above a radioisotopically dated horizon at,23.8 Ma.

DISTRIBUTION: Latest Oligocene, late midArikareean, John Day Formation, Wheeler County, Oregon.

ETYMOLOGY: The species name recognizes Michael Fingerut, who discovered and collected the holotype in the Balm Creek drainage, north-central Oregon.

DIAGNOSIS: Wolf-sized species of Temnocyon (basilar skull length, 25 cm), distinguished from T. altigenis and T. subferox by much larger size, from T. macrogenys by smaller size; differs from similarly sized T. ferox by greater inflation of the frontal paranasal sinuses (relative to braincase width, table 7) and by different form and proportions of p4–m2 and M1–2 (tables 2, 3), including a more lingually extended M1–2 with less expansion of M1 protocone region (ratio A/B, table 6), a much larger M2 and m2, a longer m2 (ratio E/F), and by a more robust, wider p4. Temnocyon fingeruti differs from T. percussor in its much smaller M1 (in the upper dentition of T. percussor only M1 survives), more elongate m1–2, stronger m1 metaconid, and larger, rectangular m2 with vestigial metaconid and more developed paraconid, and by the p4/m1 ratio (0.78 in T. fingeruti vs. 0.84 in both T. percussor and T. ferox ). Temnocyon fingeruti differs from T. altigenis , T. subferox , and probably T. ferox in P4 proportions (ratio C/D, table 6); P4 is not known in T. percussor and T. macrogenys .

REFERRED SPECIMENS: None.

DESCRIPTION: The skull of NM 280/61 is elongate (basilar length, 25 cm, table 7) as are the known skulls of T. ferox and T. subferox but differs from the short, broad skull of Delotrochanter oryktes . Cranial size and proportions are similar to those of T. ferox except for the much greater frontal sinus inflation and entirely different form of P4–M2 and p4–m 2 in T. fingeruti . Despite smaller size, a narrower snout and clearly dissimilar dentition, the profile of NM 280/61 compares with the skull form of Mammacyon ferocior . NM 280/61 approximates a large male wolf ( Canis lupus ) in rostral proportions and palatal dimensions but shows a longer postorbital cranium with broader basicranium, greater frontal sinus inflation, and smaller braincase volume. Although the teeth are similar in occlusal dimensions to those of a wolf, NM 280/61 has larger canines, more robust premolars, with a proportionately smaller shearing m1 and a longer m2–3 crushing platform. As with other John Day crania, sutures and anatomical detail are obscured by diagenetic alteration of bone. The orbital region preserves the orbital foramina nested in the elongate depression previously descibed for T. altigenis (UCMP 1549) . An orbital foramen, sphenorbital fissure, and anterior opening for the alisphenoid canal (the foramen rotundum opening internally into the canal) are situated as in that plesiomorphic species, and it is apparent that this anatomical pattern is common to all temnocyonines where the orbital region has been preserved. The basicranium and auditory region are exceptional and are discussed in the section on Basicranial Anatomy.

The mandible is gracile and slender (depth beneath m1, 32 mm; below p2, 27 mm) with toothrow length (p1–m3) of 110 mm. These teeth are worn, indicating a mature but not aged individual; the canines, particularly the lower pair, reflect some damage, with the right lower canine beveled to a rounded stub suggesting it had been broken and smoothed by abrasion during life.

Lower incisors of temnocyonines rarely survive but are preserved in T. fingeruti . The i1–3 were quite small; there is little room (, 1 cm) for them between the canines. During feeding these incisors would have been of little use. A somewhat larger i3 (length, 6.4 mm; width, 3.7 mm) contrasts with i2 (length, 5.9 mm; width, 2.9 mm) represented only by a broken root. There is no evidence of i1 that if present was placed in front of and below i2.

The canine measures, 19 mm in length,, 10 mm in width, measured at the enamel base; the symphyseal width is narrow, only 30 mm measured across the base of the canines.

The p1 is a small, peglike tooth (length, 6.9 mm; width, 4.0 mm) and is much worn.

The p2 (length, 12.1 mm; width, 5.6 mm) is much larger than p1 with its posterior slope somewhat longer than the anterior slope. A thin enamel ridge travels down both the anterior face to the anterolingual corner and the posterior face to the posterolabial cingulum. There are no accessory cusps.

The p3 (length, 15.3 mm; width, 6.6 mm) is a larger replica of p2 with a small posterior cingular shelf and a tiny basal cusp; the shelf is indented by wear on the left p3, less so on the right. There are no evident accessory cusps.

The p4 (length, 19.3 mm; width, 8.7 mm) is quite long relative to p3. There is a prominent labially situated posterior accessory cusp above a cingular shelf.

The principal cusps of p2–4 are worn flat by apical abrasion. The p2–3 are not tall relative to those in the large durophagous species of Mammacyon and Delotrochanter . They compare with p2–4 of T. altigenis but are much larger teeth.

The m1 (length, 24.7 mm; width, 10.6 mm) is a narrow, shearing carnassial that in this individual shows apical wear on trigonid and talonid cusps. Although the mandible of T. fingeruti and the wolf are of similar size, m1 is much smaller and the premolars larger in the beardog. The paraconid is mesially advanced to form a shear plane with the tall protoconid. A prominent metaconid is situated posterolingual to the protoconid. The talonid is filled by a large hypoconid; this cusp does not attain the height of the paraconid as in Mammacyon and Delotrochanter . A sinuous labial cingulum is present on the talonid but subdued on the trigonid. There is no entoconid yet a very narrow lingual talonid shelf occurs.

The elongate m2 (length, 14.8 mm; width, 8.9 mm) displays a low paraconid anterolingual to the taller, rather blunt, labial protoconid; a small metaconid is present. The m2 talonid has a low, more centrally placed hypoconid; there is no entoconid.

The rectangular m3 (length, 9.8 mm; width, 7.1 mm) has a distinct trigonid somewhat elevated above the talonid. The protoconid is connected by a curvilinear ridge to a very small metaconid. A low hypoconid is the only talonid cusp. A cingulum surrounds both the m2 and m3.

The upper dentition is one of the most complete among temnocyonines. Both toothrows are intact: width of the transverse incisor row, 24.7 mm; width between canines, 24.9 mm; a narrow palate between P1–2 (25.9 mm) widens between P3–4 (36.8 mm), and reaches its maximum breadth (59 mm) between the embrasures of the P4–M1 pair. Palatal length measured from I1 along the midline to the posterior border of the palate is 13 cm. Toothrow length from P1–M2 is 92.1 mm (P2–4, 58.7 mm; M1–2, 27.3 mm).

I1 (length, 5.5 mm; width, 2.4 mm) and I2 (length, 6.5 mm; width, 2.7 mm) are quite small, their apices worn flat. I3 is larger (length, 10.0 mm; width, 5.4 mm), heavily worn to a stub. There are short diastemata between I3 and the canine (4.8 mm), between C–P1 (3.6 mm), P1–2 (3.9 mm), P2–3 (7.0 mm), and P3–4 (2.0 mm). The small I3 of T. fingeruti contrasts in size with the huge I3s of D. oryktes and M. ferocior . Wear on the upper incisors of T. fingeruti shows that they occluded with i 1–3 in a grasping or nipping role.

The canine (length, 17.3 mm; width, 12.3 mm, measured at enamel-dentine contact) is broken and worn, but it was more robust than a wolf canine from a similarly sized skull.

P1 is a small peglike tooth (length, 7.6 mm; width, 4.7 mm) with a low vertical anterior face and a posterior slope lacking accessory cusps.

P2 is a larger triangular tooth (length, 13.4 mm; width, 5.7 mm) with a posterior slope slightly longer than the anterior face. There are no accessory cusps.

P3 is somewhat larger (length, 16.1 mm; width, 7.0 mm) than P2 with anterior and posterior faces as in P2 but having a broader heel than P2. Heavy wear on the posterior slope prevents identification of an accessory cusp but it was probably not present.

P4 is a short carnassial (length, 22.0 mm; width, 15.4 mm) with a prominent shear plane beveling the lingual faces of paracone and metastylar blade. A blunt protocone is situated directly lingual to the paracone. The posterior half of the protocone occluded against the m1 paraconid, evidenced by an elliptical wear facet, whereas the anterior face of the protocone was abraded by the p4 accessory cusp. Labial and lingual cingula are present but the anterior face of P4 and the adjacent heel of P3 were deeply worn by the principal and accessory cusps of the large p4.

The principal cusps of P1–3 exhibit flat apical wear facets. This blunting of cusps also occurred on the M1 paracone and metacone (with minor apical wear on M2 paracone) and the paracone and metastylar blade of P4. P4 wear included a shear component that extended posteriorly along the lingual faces of the M1 paracone-metacone and M2 paracone, evidenced by shear facets on these molars.

M1 (length, 17.1 mm; width, 22.4 mm) retains a plesiomorphic occlusal form little different from that of T. altigenis . The paracone and slightly smaller metacone are bordered by a labial cingulum with developed parastyle. The cingulum thins on the margins of M1 at the level of the protocone basin but then thickens to form a prominent posterolingual cingulum around the protocone, which does not equal the strongly swollen M1 lingual cingula observed for Mammacyon and Delotrochanter . The protocone is situated near the anterior margin of the tooth and is more sharp-crested and less bunodont. A preprotocrista runs anterolabially from the protocone to the anterior cingulum, and a short weak postprotocrista intersects the posterior cingulum.

M2 (length, 9.6 mm; width, 17.4 mm) is smaller and of a different form than M1; the anterior margin is convex, the posterior concave. The paracone is much larger than the low reduced metacone yet the lingual face of the two cusps forms a vertical shear plane. The labial and anterior sides of M2 are bordered by a cingulum that thickens to form a wide lingual swelling. A minute protocone situated in the center of an enamel flat retains an anterolabially directed preprotocrista and a tiny postprotocrista. The posterior margin of M2 is worn by the anterior face of m3 since there is no M3.

In T. fingeruti , crushing/shearing occlusion was accomplished by p4–m2 and P3–M2. More anterior teeth served to grasp the food and, via the action of the tongue, passed it back to the carnassials and molars.

DISCUSSION: The skull and mandibles of NM 280/61 represent one of the bestpreserved North American temnocyonines. The species preserves the most wolflike dentition of any temnocyonine and exhibits an attritional dental wear pattern much like that known for Canis lupus . Despite some crushing of the skull that collapsed the zygomata and shifted the rostrum laterally relative to the frontal region, the cranium, teeth, and basicranial anatomy are exceptional. NM 280/61 demonstrates that a plesiomorphic temnocyonine dental pattern continued in the Pacific Northwest to very near the Oligocene-Miocene boundary, currently placed at 23.03 Ma ( Gradstein et al., 2004). Because NM 280/61 occurs only, 20 m above a radiometric date of 23.8 Ma, its stratigraphic level places it in the latest Oligocene.

NM 280/61 is the stratigraphically youngest John Day temnocyonine yet discovered; whether Great Plains early Miocene temnocyonines such as T. macrogenys and Delotrochanter existed in the Pacific Northwest is not known. Absence of early Miocene temnocyonines in the John Day beds could simply reflect the more limited representation of sediments of that age, which are often unfossilferous. However, large daphoenine and amphicyonine beardogs have been found in early Miocene John Day strata of early Hemingfordian age ( Borocyon , Amphicyon: Hunt and Stepleton, 2004 ), suggesting that they replaced the temnocyonines.

Figures

Fig. 16. Holotype cranium and mandibles of Temnocyon fingeruti (NM 280/61), from Balm Creek, Haystack Valley Member (revised), John Day Formation, Wheeler Co., Oregon. This skull was found 62 ft (,19 m) above a tuffaceous horizon dated to,23.8 Ma (Hunt and Stepleton, 2004).

Fig. 17. Holotype palate and upper dentition (A, left and right I1–3, C, P1–M2; B, stereopair with right P3–M2) of Temnocyon fingeruti (NM 280/61), Balm Creek, Haystack Valley Member (revised), John Day Formation, Wheeler Co., Oregon. Note occlusal wear on P3–M2.

Fig. 18. Holotype left (A) and right (B) mandibles of Temnocyon fingeruti (NM 280/61), from Balm Creek, Haystack Valley Member (revised), John Day Formation, Wheeler Co., Oregon, both in labial view (left c, p2–m3; right c, p1–m3).

Fig. 19. Occlusal views of the mandibular dentition of the holotype of Temnocyon fingeruti (NM 280/ 61). Balm Creek, Haystack Valley Member (revised), John Day Formation, Wheeler Co., Oregon. A, left and right p2–m3; B, stereopair of p3–m3. Note apical wear on premolars and carnassials.

Fig. 68. Holotype basicranium of Temnocyon fingeruti (NM 280/61), Balm Creek, Haystack Valley Member (revised), John Day Formation, Wheeler Co., Oregon. A, epoxy cast of basicranium showing left and right auditory bullae each composed of an ectotympanic, an E1 caudal entotympanic forming the medial wall, and an E2 caudal entotympanic completing the posterior wall of the bulla. B, basicranium of NM 280/61 in ventral view (stereopair). C, detail of the auditory region and the principal bulla elements (stereopair). For abbreviations, see page 5.