Lophialetidae Matthew and Granger, 1925

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 : 28-30

Family Lophialetidae Matthew and Granger, 1925 Lophialetidae gen. et sp. indet.

Fig. 5A, B.

Referred material.—GSP−UM 6505, an isolated right M3; GSP−UM 6540, a left dentary with m2–3.

Description.—Specimen GSP−UM 6505 was found at GSP−UM locality GH−45 about 3 kilometers southeast of Kingri, and is a well−preserved, strongly lophodont M3 with a length of 14.6mm and a width of approximately 16.2mm. The parastyle is rounded and distinct, separated from the paracone but placed close to it ( Fig. 5B). The paracone is the highest cusp of the tooth, with a markedly convex labial side and a flat lingual side. The metacone is strongly reduced, almost completely flat and barely higher than the rest of the ectoloph, forming an anteroposteriorly directed flange. The protoloph and metaloph are well−developed, unnotched and as high as the ectoloph. The protoloph is distinctly longer and slightly more robust than the metaloph. The protocone and hypocone are distinct and equal in height, but the protocone is more robust. The anterior cingulum is distinct but narrow and there is a small, short posterior cingulum. There are no labial or lingual cingula.

Specimen GSP−UM 6540 was collected from GSP−UM locality GH−46, in the same horizon as specimen GSP−UM 6505, about 500 meters southeast of locality GH−45. This

MISSIAEN AND GINGERICH—EOCENE TAPIROMORPHS FROM PAKISTAN 29

20 mm

specimen consists of a partial dentary with strongly lophodont m 2–3 in place, preceded by five alveoli for the posterior root of p3 and the roots of p4 and m1 ( Fig. 5A). Both molars are severely damaged, but m2 was approximately 14.6 mm long with an estimated trigonid width of 8.6mm, while the width of the m3 trigonid was about 8.8 mm. Both molars have a well−developed but relatively low paracristid that descends anterolingually from the protocone in a smooth curve. The protoconid is distinct and more robust than the metaconid, but is fully integrated into the paracristid and protolophid. The metaconid is positioned posterolingual to the protoconid and has a distinct anterolabial rib jutting out of the protolophid. The talonid is not well preserved on either of the molars, but the hypolophid was high and distinct, and oriented parallel to the protolophid. The cristid obliqua runs anterolingually from the hypoconid towards the posterolingual corner of the protoconid, but shows a distinct notch at the point of attachment to the protolophid.

Comparison.—Based on size and morphological compatibility, GSP−UM 6505 and GSP−UM 6540 can be readily assigned to the same taxon, which is characterized by strong lophodonty, with the upper molars being marked by a prominent parastyle, a lack of conules and a metacone that is reduced to an anteroposteriorly directed flange, at least on M3. The lower molars show a similarly distinct lophodonty with a prominent but low paracristid and cristid obliqua. The strongly lophodont condition is typical of ceratomorph perissodactyls, and within this group the flat metacone and the distinct but not strongly developed paracristid and cristid obliqua are found only in the Asian endemic family Lophialetidae and in primitive rhinocerotoids such as Hyrachyus ( Radinsky 1969) .

The wear pattern on GSP−UM 6505, with the protoloph wearing down from the top and the metaloph wearing down from the front, supports this assignment to either lophialetids or rhinocerotoids ( Radinsky 1965). Both groups can be unequivocally distinguished based on the upper premolars and the development of the m3 hypoconulid lobe, but this information is unfortunately missing for the taxon from the Ghazij Formation. The Ghazij material however differs from Hyrachyus by an uncompressed and less labial parastyle, a paracone with a more convex labial side and a flat lingual side, the absence of an anterolingual rib on the lower molar protoconid, and possibly the absence of an upper molar labial cingulum.

The Ghazij taxon differs from more derived rhinocerotoids by a subquadrangular M3, an unreduced parastyle, and by a low paracristid and cristid obliqua ( Prothero et al. 1989). Within Lophialetidae , the morphology of the Ghazij taxon seems to be intermediate between Schlosseria on the one hand and Lophialetes and Eoletes on the other ( Matthew and Granger 1925; Radinsky 1965; Lucas et al. 1997), most markedly because of the shape of the M3 metacone and the height of the lophs. The Ghazij taxon resembles Schlosseria magister in its parastyle morphology and a less triangular M3 with a more transverse metaloph. The Ghazij taxon is, however, closer to Lophialetes and Eoletes in size, as well as in terms of its flat lingual side of the paracone.

Kalakotia simplicidentata from the middle Eocene of India and Pakistan is sometimes placed in the family Lophialetidae ( Ranga Rao 1972; Russell and Zhai 1987; Thewissen et al. 2001). Other studies of perissodactyl evolution do, however, show that Kalakotia is not a lophialetid, most clearly by the absence of a complete lophoid loop on P3–4 ( Hooker 1989; Schoch 1989). Although there are some similarities between the Ghazij material described here and Kalakotia , the Ghazij taxon differs from Kalakotia by its larger size and less anteroposteriorly elongated shape, as well as by higher lophs of the

http://dx.doi.org/10.4202/app.2010.0093

upper and lower molars. The Ghazij taxon additionally differs from Kalakotia by an M3 with a weaker parastyle, a more flattened paracone and metacone, and a different wear pattern, as well as by lower molars with an anterolingually flat paracone and a notched cristid obliqua.

Based on the similarities and differences noted above, we suggest that GSP−UM 6505 and GSP−UM 6540 represent a new, previously unknown species of Lophialetidae . The phylogenetic relationships within this family are, however, unclear, even for taxa where many specimens are available (see Lucas et al. 1997). We therefore refrain from suggesting more detailed affinities or formally naming a new taxon.

Stratigraphic and geographic range.—Late early Eocene (Ypresian); upper part of the upper Ghazij Formation; Kingri area, Balochistan ( Pakistan).