Enaliarctos mealsi Mitchell and Tedford, 1973

Poust, Ashley W. & Boessenecker, Robert W., 2018, Expanding the geographic and geochronologic range of early pinnipeds: New specimens of Enaliarctos from Northern California and Oregon, Acta Palaeontologica Polonica 63 (1), pp. 25-40 : 28-30

publication ID	https://doi.org/ 10.4202/app.00399.2017
persistent identifier	https://treatment.plazi.org/id/03D287F7-3F5A-FF93-FCEF-FC9033A6FF12
treatment provided by	Felipe
scientific name	Enaliarctos mealsi Mitchell and Tedford, 1973
status

Treatment

Figs. 3 View Fig , 4 View Fig ; Tables 1, 2.

Material.— UCMP 114474 View Materials , isolated left mandible (collected by Bruce J. Welton, October 6, 1975) ; UCMP 276804 View Materials , partial metacarpal (collected by RWB and Richard Hilton, July 21, 2015); from Skooner Gulch I, Mendocino County, California ( UCMP locality V75135); Skooner Gulch Formation, early Miocene (23.03–22 Ma ) .

Description.—UCMP 114474 includes the anterior left mandible, missing the posterior end behind the m2 alveolus ( Fig. 3 View Fig ). The preserved portion of the horizontal ramus is rectangular, deepening only at the root of the canine located ventral of the p2. The anteroventral margin is broken and the genial tuberosity is missing. Two large (4.0 mm and 2.0 mm) mental foramina are positioned on the middle of the mandible below p2 and p3, respectively. The dorsal margin is flat except where the alveolar rims rise above this surface.

Dentition: The anterior portion of UCMP 114474 is missing, including the incisors. The canine is in place despite lacking much of the bone surrounding the root. It is relatively small and dorsoventrally short with mild posterior curvature. A shallow buccal wear facet is seen on the posterior bulge of the crown as in some other carnivores. The canine bears two cristae just lingual of its posterior edge. These converge slightly towards the tip, but do not meet.

All preserved postcanine teeth are double-rooted, but alveoli for p1 and m2 suggest these teeth were single-rooted. The p2 has a high but anteroposteriorly narrow crown with a large, distinct, nearly recurved, conical paraconid, no clear metaconid, and a low, crest-like hypoconid encircling a shallow posteromedially placed talonid basin. The p3 crown bears a larger, robust and conical paraconid, a high protoconid, a small metaconid, and a small hypoconid positioned posteriorly on a crest defining a somewhat larger talonid basin. The p4 continues the trend of enlarging the paraconid, possesses a high, pointed protoconid, and a large metaconid; the hypoconid resembles that of p3 but encircles a more deeply excavated talonid basin. This p4 talonid basin is separated into posterior and posteromedial portions by the base of the metaconid, which drops precipitously into the basin. In dorsal view the protoconid of p4 and m1 have two distinct wear surfaces separated by a narrow ridge. The metaconids of p3–m1 are high and positioned apically near the protoconid. All premolars exhibit moderately developed labial cingula and smaller, but distinct lingual cingula.

The m1 has a dorsoventrally lower crown with a lower, sharper protoconid than in the premolars. The metaconid is conical but apically rounded and offset lingually from the protoconid. The hypoconid is large, labiolingually broad and more apically prominent than in the premolars. No diastemata are present in the postcanines.

Metacarpal: UCMP 276804 is a partial distal metacarpal of uncertain position ( Fig. 4 View Fig ). Proximally the cross-section is nearly circular. The distal end is somewhat hemispherical and bears a slight keel; it is rounded in dorsal view, differing from the flattened joint in extant pinnipeds. The keel protrudes strongly on the palmar side, suggesting a wide range of motion in the foreflipper of Enaliarctos , perhaps relating to prey acquisition and processing (e.g., Hocking et al. 2016).

Remarks. — The mandible, UCMP 114474, is identifiable as Enaliarctos in exhibiting a lingual bulge on the base of the canine crown, postcanine teeth with apically positioned, strongly developed metaconid cusps and trenchant paraconid cusps. Advanced wear of the cusps suggests this specimen represents an adult, and a relatively narrow canine in comparison with other enaliarctines suggests that UCMP 114474 is a female ( Cullen et al. 2014). UCMP 114474 differs from Enaliarctos emlongi in exhibiting well-developed labial cingulum and cuspate posterolingual cingulum, and shares these features with E. mealsi and E. barnesi . UCMP 114474 differs from E. barnesi in exhibiting a deeper notch between the paraconid and protoconid on the m1, a lower m1 protoconid, and more apically prominent metaconids on p3–p4. These differences are not noted in comparison with isolated lower teeth referred to E. mealsi ( Mitchell and Tedford 1973; Barnes 1979), the presumed p3–p4 and m1 of which are indistinguishable from UCMP 114474. Owing to these shared features (prominent metaconids, extensive labial and lingual cingulum, trenchant paraconids, low protoconid on m1 with deeper notch anteriorly) we refer UCMP 114474 to Enaliarctos mealsi . We note that E. barnesi and E. mealsi may be synonymous (see below) and another possibility may be that these dental features are attributable to sexual dimorphism, as the E. barnesi holotype is a presumed male ( Cullen et al. 2014) and UCMP 114474 is a presumed female (see above). The metacarpal, UCMP 276804, is tentatively referred as Enaliarctos sp. , cf. E. mealsi owing to its cylindrical diaphysis and strongly keeled distal trochlea ( Berta 1991); metapodials are unknown for other enaliarctines ( Pacificotaria , Pinnarctidion , Pteronarctos ) or the enliarctine-like basal odobenid Proneotherium , rendering this referral provisional.