Litolophus ghazijensis, Missiaen & Gingerich, 2012

Missiaen, Pieter & Gingerich, Philip D., 2012, New early Eocene tapiromorph perissodactyls from the Ghazij Formation of Pakistan, with implications for mammalian biochronology in Asia, Acta Palaeontologica Polonica 57 (1), pp. 21-34 : 30

Litolophus ghazijensis sp. nov.

Fig. 5C.

Etymology: Referring to the Ghazij Formation in Pakistan, where the specimen was found.

Holotype: GSP−UM 6519, an isolated left M3.

Type locality: GSP−UM locality GH−46, Balochistan Province, Pakistan.GPS coordinates of the type locality are: 30.4158° N, 69.7862° E .

Type horizon: Late early Eocene (Ypresian); upper part of the upper Ghazij Fm; Kingri area, Balochistan ( Pakistan).

Referred material.—GSP−UM 6534, right upper molar fragment.

Diagnosis.—Chalicotherioid similar to Litolophus gobiensis in size, in lacking a mesostyle, and in having a posterolabially rotated metacone; differing from L. gobiensis in having a more posterior paraconule, in having a stronger posterolabial rotation of the metacone, and in having a metaloph that is parallel to the protoloph and not posterolabially rotated and in line with the ectoloph as in L. gobiensis .

Description.—Specimen GSP−UM 6519 is an isolated M3 with a length of 27.3 mm and a width of 28.3 mm. The parastylar lobe is prominently projecting anterolabially, but the parastyle cusp itself is mostly flattened. The paracone is distinct and bears a marked labial rib. There is no mesostyle. The metacone is positioned posterior to the paracone and is not much higher than the ectoloph, but still clearly visible. The metacone is flattened, with an anterolingual−posterolabial orientation roughly parallel to the parastyle. The strong protoloph attaches high onto the ectoloph, but is distinctly notched lingual to the paraconule. The paraconule is situated at the labiolingual midpoint of the protoloph, but is markedly posteriorly displaced from the main axis of the latter. The protocone is a robust cusp that extends posteriorly from the protoloph. The distinct metaloph has no sign of a metaconule and is slightly higher than the protoloph and roughly parallel to it. The hypocone is placed directly posterior to the protocone and is slightly higher than the protocone, but much less robust. GSP−UM 6519 has distinct anterior and posterior cingula and no real lingual cingulum. There is some minor damage to the labial edge of the tooth, but the labial cingulum was probably weak.

Specimen GSP−UM 6534 is a partial hypocone of a right upper molar found at locality GH−45, and is identical to GSP−UM 6519 in all preserved features.

Comparison.—A molar protoloph interrupted by a paraconule, and a high molar metaloph without a metaconule are considered two typical and diagnostic traits of the superfamily Chalicotherioidea ( Radinsky 1964) . Within this group, the absence of a mesostyle is seen only in the genera Litolophus , Lophiaspis , Paleomoropus , and Protomoropus , although the chalicothere affinities of the latter three genera have been questioned ( Fischer 1977; Lucas and Kondrashov 2004). Litolophus ghazijensis differs from Paleomoropus and Protomoropus by its significantly larger size, stronger lophs, and more projecting parastyle. L. ghazijensis differs from Lophiaspis in having a less labial paracone.

Litolophus ghazijensis differs from these three genera and resembles L. gobiensis by a posteriorly displaced paraconule and protocone, and by a posterolabially rotated metacone. In addition, it resembles L. gobiensis in having a relatively deeply notched protoloph lingual to the paraconule, in having a high hypocone with posterolabial and anterolingual flanges, and in having an indistinct accessory crest that is present posterolingual to the paracone of GSP−UM 6519 and in some L. gobiensis specimens ( Bai et al. 2010). L. ghazijensis , however, differs from L. gobiensis by a more vertical parastyle with a less convex anterolabial side and by a stronger posterior displacement of the paraconule. Additionally, in L. ghazijensis the metacone is more strongly rotated and is parallel to the parastyle, whereas the metaloph is not rotated as in L. gobiensis but remains parallel with the protoloph as in other Eocene chalicotheres.

Although the chalicothere material from the Ghazij Formation is currently very limited, the morphology of GSP−UM 6519 is highly diagnostic, clearly indicating affinities with the genus Litolophus and differences from L. gobiensis .