Camelops hesternus Leidy, 1854

Zazula, Grant D., Macphee, Ross D. E., Hall, Elizabeth & Hewitson, Susan, 2016, Osteological assessment of Pleistocene Camelops hesternus (Camelidae: Camelinae: Camelini) from Alaska and Yukon, American Museum Novitates 2016 (3866), pp. 1-46 : 6-8

Camelops hesternus Leidy, 1854

MANDIBLE AND LOWER DENTITION

Referred specimens: F: AM 35172 ( Gold Hill , Alaska), mandible fragment, juvenile, with unworn, partially erupted p4–m1 ( fig. 3 A–C); F : AM 34631 ( Cripple Creek , Alaska), right mandible fragment, with heavily worn m1–m3 ( fig. 3 D–F); F : AM 35168 (Fairbanks Creek, Alaska), anterior mandible fragment with symphysis, diastema, and roots of right p4 ( fig. 3 , G, H); NMC 42549 ( Sixtymile Loc. 3, Yukon), left, juvenile, mandible with dp3–dp4, m1, lacking symphysis and coronoid process ( fig. 3 I–L); F : AM 144676 ( Cripple Creek , Alaska), heavily worn left m3, roots broken off ( fig. 4 A–C); F : AM 35154 ( Cripple Creek , Alaska), heavily worn, right m3, roots broken off ( fig. 4 D–F); F : AM 35169 ( Gold Hill , Alaska), right, moderately worn m2?, root of posterior lobe sampled, anterior root broken off ( fig. 4 G–I); F : AM 35170 ( Dawson Cut , Alaska), relatively unworn, left m1 or m2, roots and anterior margin broken off ( fig. 4 J–L); F : AM 35173 ( Gold Hill , Alaska), left m2, anterior cusp and root missing ( fig. 4 M–O) .

Description: The most complete mandible in this collection represents a juvenile ( NMC 42549), described below. This and others specimens described here exhibit several features consistent with their allocation to Camelops hesternus ( Webb, 1965) , including: (1) sharp, labially concave diastemal crest ( fig. 3H, L ); (2) deep horizontal ramus featuring slight concavity below diastema and relatively straighter ventral border in lateral view compared to other BARCs ( fig. 3 I–K); (3) large mental foramen situated low on the mandible, below posterior end of canine root ( fig. 3G, J ); (4) distinct angular “spur-shaped” process present on posterior margin of ascending ramus, below condyle but above level of horizontal ramus ( fig. 3 I–K), and lacking inflection seen in other camelines ( Harrison, 1985). The mandibular fragments representing mature adult individuals (F: AM 34631 and F: AM 35168) exhibit horizontal rami that are much broader transversely and more robust than in other BARCs ( table 1 ).

Individual mandibular dental loci can be readily differentiated from those of other BARCs. Key features consistent with descriptions and illustrations of Camelops hesternus ( Webb, 1965; Dalquest, 1992) include: (1) lower molars large, highly hypsodont ( fig. 4G, H ), and relatively long mesiodistally compared to their transverse widths ( fig. 4 A–F); (2) molar lophs separated by deep, narrow valleys on the labial side ( fig. 4D, F ), relatively flat on the lingual side ( fig. 4E, F ); (3) loph crests higher and sharper lingually than labially, and more strongly developed on anterior cusps than posterior ( fig. 4B ); (4) typical wedge shape when viewed in lateral profile, with the occlusal surface much wider than the base, best exemplified by the unworn m2 F: AM 35169 ( fig. 4G, H ); (5) long, thin, weakly U-shaped infundibula (lakes) on occlusal surfaces, opening lingually, with thicker enamel on lingual side than labial and lacking internal cementum ( fig. 4C, F, I,L ). Only one specimen, F: AM 35173 (partial left m2; fig. 4O ) exhibits infundibular cementum; (6) F: AM 35169, an unworn m2, presents a weakly developed mesiolabial enamel fold or “llama buttress” ( fig. 4I ), a typical feature of Camelops hesternus lower molars ( Webb, 1965, Dalquest, 1992). However, “llama buttresses” are missing from most of our sample of mandibular molars, presumably as a consequence of wear.

The juvenile NMC 42549 possesses deciduous premolars dp3 and dp4 and an unerupted m1. Both premolars are notably molariform, though splayed roots can be detected radiographically ( fig. 3K ). The dp4 is strongly trilobate, resembling an m3, while dp3 is weakly bilobate, resembling a deformed m2 ( fig. 3L ). Due to marked interproximal wear (a common feature of cameline lower dentitions; see Meachen, 2003), the dentition of F: AM 34631 appears very compressed ( fig. 3D ). Enamel has been almost completely removed from the mesial and distal surfaces of m1 and m2, with the result that the mesial margin of the latter is inset into the distal margin of the former. The degree of mandibular molar wear on this individual suggests that it was an old, but not yet senile, individual (see Dalquest, 1992).

Figures

FIG. 3. Camelops hesternus mandibles from Alaska and Yukon. F:AM 35172: A, occlusal, B, labial, and C, lingual views. F:AM 34631: D, occlusal, E, labial, and F, lingual views. F:AM 35168: G, labial (right side) and H, occlusal views. NMC 42549: I, lingual, J, labial, K, radiograph of labial side (showing m1 within alveolus), and L, occlusal views.

FIG. 4. Camelops hesternus teeth from Alaska and Yukon. F:AM 144676, m3: A, labial, B, lingual, and C, occlusal views. F:AM 35154, m3: D, labial, E, lingual, and F, occlusal views. F:AM 35169,?m2: G, labial, H, lingual, and I, occlusal views. F:AM 35170, m1 or m2: J, labial, K, lingual, and L, occlusal views. F:AM 35173, m2: M, labial, N, lingual, and O, occlusal views. F:AM 35153, M3: P, lingual, Q, labial, and R, occlusal views. F:AM 35171, M1 or M2: S, lingual, T, labial, and U, occlusal views.