Gandheralophus minor, 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 : 23-26

Gandheralophus minor sp. nov

Figs. 2A–F, 3A–D; Table 1.

Etymology: From Latin minor , smaller, referring to the small size of the species, which is smaller than any other isectolophid currently known.

Holotype: GSP−UM 6770, a partial dentary with right p3–m 3 in situ.

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

Type locality: Gandhera Quarry , Balochistan Province, Pakistan. GPS coordinates of the type locality are: 30.3852° N, 69.8238° E .

Type horizon: Late early Eocene (Ypresian); upper part of the upper Ghazij Formation; Gandhera Quarry, Balochistan ( Pakistan).

Referred material.—GSP−UM 4686, left p4−m2; GSP−UM 4692, left DP4−M1; GSP−UM 4696, right DP3−4; GSP−UM 4698, right m2−3; GSP−UM 4700, right p4−m3; GSP−UM 4701, left m1−3; GSP−UM 4710, left P4−M3; GSP−UM 4715, right M1−2; GSP−UM 4716, right P3−M3; GSP−UM 4719, left dp4−m1; GSP−UM 4720, left m2−3; GSP−UM 4721, right m2−3; GSP−UM 4724, left P4−M2; GSP−UM 4787, right P3; GSP−UM 4788, right p4; GSP−UM 4789, right p4; GSP−UM 4834, right m3; GSP−UM 4835, left m3; GSP−UM 4838, left p4−m1; GSP−UM 4915, right DP4; GSP−UM 4916, left M2; GSP−UM 5275, left M3; GSP−UM 5277, right M2; GSP−UM 5279, left M2; GSP−UM 5280, left M2; GSP−UM 5282, right M3; GSP−UM 5284, left M2; GSP−UM 5285, right M3; GSP−UM 5286, right M3; GSP−UM 5288, left M2; GSP−UM 5290, left M3; GSP−UM 5292, left M3; GSP−UM 5293, left M1; GSP−UM 5294, right M1; GSP−UM 5295, right M2; GSP−UM 5300, left M2; GSP−UM 5301, right M1; GSP−UM 5324, right M1; GSP−UM 5326, left Max. M1−2; GSP−UM5329, right M1; GSP−UM 5352, right m1; GSP−UM 5353, left m2−3; GSP−UM 5354, left m2; GSP−UM 5355, right m3; GSP−UM 5359, left m3; GSP−UM 5361, left m3; GSP−UM 5379, left p4; GSP−UM 5380, left dp4; GSP−UM 5431, left P3−M2; GSP−UM 5433, right M2−3; GSP−UM 5439, left M1; GSP−UM 5440, left M2; GSP−UM 5442, right M1; GSP−UM 5444, right m3; GSP−UM 5445, right p4; GSP−UM 6222, left MX; GSP−UM 6256, right M1; GSP−UM 6257, left M3; GSP−UM 6258, right M1; GSP−UM 6259, left M2; GSP−UM 6261, left M2; GSP−UM 6263, left M2; GSP−UM 6264, left M2; GSP−UM 6266, right MX; GSP−UM 6267, left M1; GSP−UM 6268, left P4; GSP−UM 6269, left P4; GSP−UM 6270, left m1−2; GSP−UM 6271, left m1; GSP−UM 6273, right m3.

Diagnosis.— G. minor differs from G. robustus in being approximately 15% smaller; in having a P4 with a complete metaloph; in having upper molars with a larger, more rounded parastyle cusp, a more closely placed paracone and metacone, and a more posteriorly directed metaloph; in having an M3 with a more reduced posterior region that sometimes presents accessory cusps or crests; in having a p1, a larger p2 and a more molariform p3; and in having an open trigonid on p4 and the lower molars.

Description.—P3 is a small, premolariform tooth. The labial side bears the small but distinct parastyle and the larger, closely spaced paracone and metacone. The lingual part of P3 bears a protocone, a distinct protoloph with a faint paraconule, and a weak metaloph. There is also a small anterior cingulum, and a large, rounded posterior cingulum without a hypocone.

P4 is larger than P3 and differs from it by a less closely spaced and slightly anteroposteriorly compressed paracone and metacone, and by a relatively larger protocone.

M1 is rectangular to somewhat trapezoidal in shape and slightly wider than long. The parastyle is placed anterior to the paracone and smaller than the latter. The metacone is slightly lower than the paracone, and is placed posterolingual to and clearly separated from the latter. The protoloph often presents a reduced paraconule and attaches to the ectoloph between the parastyle and the paracone. The metaloph attaches to the anterolingual corner of the metacone and lacks a metaconule. Labial and lingual cingula are variably developed, ranging from almost absent ( Fig. 2C) to complete and continuous ( Fig. 2A, D).

M2 is similar to M1, but markedly larger and slightly more trapezoidal.

M3 is similar in size to M2, but tapers strongly posteriorly and has a rounded posterior border. The M3 metacone is much smaller in size than on M1–2 and transversely compressed. The hypocone has a less lingual position than on M1 or M2. On the posterior part of M3, accessory structures are variably developed, including small cuspules on the metaloph or the posterior border, or even a crest running

MISSIAEN AND GINGERICH—EOCENE TAPIROMORPHS FROM PAKISTAN 25

20 mm

from the middle of the metaloph to the posterior border of M3 ( Fig. 2B).

DP3 is subquadrate with the anterior half transversely narrower than the posterior half, and with a well−separated paracone and metacone ( Fig. 2F). A short protoloph runs anterolabially from the protocone, and a second, incomplete crest runs posterolingually from the protocone to the base of the metacone. The hypocone of DP3 is clearly developed, but does not form a metaloph.

DP4 is fully molariform, mainly differing from M 1 in being smaller and relatively narrower transversely.

The anterior lower dentition of G. minor is unknown, but

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

the holotype GSP−UM 6770 ( Fig. 3A) and specimen GSP−UM 5445 ( Fig. 3D) show the presence of a diastema, one large alveolus and two smaller alveoli in front of p3. These can be interpreted as the postcanine diastema, the large single root of p1 and the two roots of p2, which means that there was no diastema between p1 and p2. Based on the alveoli in GSP−UM 5445, p2 was about 10 percent shorter than p3.

The p3 is subrectangular and premolariform. The paracristid is short and placed anterolingual to the strong protoconid. The metaconid is slightly smaller than the protoconid and placed posterolingual to it. The talonid has one labially placed cusp that is connected to the base of the protoconid.

The p4 paracristid is much better developed than on p3, forming a crest that descends anteriorly from the protoconid and then curves lingually. The p4 protoconid and metaconid are subequal in size, with the metaconid placed directly lingual and only slightly posterior to the protoconid. The p4 talonid is slightly basined, but usually presents only a single, large and labially placed cusp.

The m1 is rectangular, with the protoconid and hypoconid subequal to or slightly more robust than the metaconid and entoconid. Wear is stronger on the labial side, lowering the labial cusps and crests faster than their lingual counterparts. The trigonid is short, with the paracristid running down only a little from the protoconid before abruptly turning lingually. The protolophid and hypolophid are distinct, but somewhat notched, and are oriented transversely or just slightly obliquely. The hypoconulid is strongly reduced, forming only a small cusp pressed against the middle part of the hypolophid.

The m2 is very similar to m1, mainly differing from it by its larger size and more robust appearance.

The m3 is similar in width to m2, but is distinctly longer and tapers strongly behind the trigonid. m3 has a distinct, basined hypoconulid lobe. The hypoconulid is usually robust and placed on the midline of the tooth or somewhat labial to it, with a posthypocristid running anteriorly towards the hypolophid. The hypoconulid lobe is variable in its development ( Fig. 3A, B). In specimens where it is more strongly developed, it is more clearly basined, with a more labially placed hypoconulid and often an accessory cuspule lingual to the latter.

The dp4 is similar to m1, but transversely narrower, with a more anteriorly projecting paracristid and a smaller hypoconulid ( Fig. 3C).