Pakotitanops latidentatus West, 1980

Mihlbachler, Matthew C., 2008, Species Taxonomy, Phylogeny, and Biogeography of the Brontotheriidae (Mammalia: Perissodactyla), Bulletin of the American Museum of Natural History 311 (1), pp. 1-475 : 361-364

Pakotitanops latidentatus West, 1980

HOLOTYPE: H-GSP 1050, a maxillary fragment with left M2 and roots of M3.

TYPE LOCALITY: H-GSP locality 146, Kuldana Formation, Ganda Kas area, Pakistan.

AGE: Middle Eocene.

DETERMINATION: Problematic taxon; the species is probably valid, but the holotype is insufficient for a thorough description or adequate diagnosis.

REMARKS

West (1980) described Pakotitanops latidentatus from a heavily worn M2 (H-GSP 1050) (fig. 186). Thewissen et al. (2001) described several more highly fragmentary specimens, all from the Kuldana Formation of the Ganda Kas area. Many of the diagnostic features of this specimen, as listed by West (1980), such as the weakly developed ectoloph and the wide length/width ratio have to do with the fact that the holotype is severely worn, and its proportions have been significantly altered by wear. The tooth is too worn to make precise measurements. However, it is much larger than ‘‘ Eotitanops ?’’ dayi and Mulkrajanops moghliensis ; it seems similar in size to many North American Bridgerian and Uintan hornless brontotheres such as Palaeosyops , Telmatherium , and Dolichorhinus . The M2 of Pakotitanops latidentatus has a paraconule similar in size to that of Palaeosyops and Mesatirhinus , but this structure is much larger than the occasional paraconules seen on the molars of Dolichorhinus and Telmatherium . H-GSP 1050 exhibits a distinct central molar fossa, a character not seen in Palaeosyops or Mesatirhinus . Among similarly sized brontotheres, only Dolichorhinus has central molar fossae but also retains vestigial paraconules. The combination of a central molar fossa and a Mesatirhinus -sized paraconule seems unique. The holotype of Pakotitanops latidentatus seems to represent a valid species, although the present material is insufficient to differentiate it from Dolichorhinus (a species where the paraconule is intraspecifically polymorphic).

Mulkrajanops moghliensis Kumar and Sahni, 1985

HOLOTYPE: VPL/K 563, a skull containing partial dentition of both sides.

TYPE LOCALITY: Maroon Shales, Upper Subathu Formation exposed West of Moghla on the Metka-Moghla road, Rajauri District, Pakistan.

AGE: Middle Eocene.

DETERMINATION: Problematic taxon; this species is probably valid, though it might not be a brontotheriid. A reanalysis of this species is needed.

REMARKS

Kumar and Sahni (1985) named Mulkrajanops moghliensis from a partial skull (VPL/ K 563) of a species similar size to Eotitanops (fig. 187). No other specimens are referred to this species. I was unable to directly examine the holotype; therefore, I refer to the figures and description of Kumar and Sahni (1985) but point out the following interesting details that seem to differentiate it from other brontotheres of similar size. P1 is advanced in that it has a large paracone and metacone. There is no P1–P2 diastema. The remaining premolars are unusually elongate, and P2 bears a large paraconule. M1 has a large lophoid paraconule similar to that of Eotitanops . M3 is the only complete molar; it is squarish in outline, although it lacks a hypocone. Unlike other brontotheres, the upper molars do not appear to have had well-developed mesostyles. Mulkrajanops moghliensis further differs from North American Eotitanops in the absence of a long P1– P2 diastema and the more complex morphology of the P1. It differs from North American Eotitanops and ‘‘ Eotitanops ?’’ dayi in the more squarish M3 and possibly in the more elongated cheek teeth. Additionally, it can be distinguished from other small species such as Microtitan by the relatively steep angle and shorter height of the molar ectoloph and the presence of a large M1 paraconule. Mulkrajanops moghliensis is possibly a valid species of an unusual brontothere-like animal. However, judging from

(C) left M3, (D) right M1, (E) right P1–P4. (Scale bars 5 1 cm). Modified from Kumar and Sahni (1985).

the figures provided by Kumar and Sahni (1985), its identification as a brontothere is questionable; although many aspects of its dentition, such as the isolated lingual molar cusps, are certainly consistent with a brontotheriid, the absence of a well-developed molar mesostyle is different from other brontotheres and their probable sisters, Lambdotherium and Danjiangia , all of which have conspicuous labially expanded molar mesostyles. The published figures of Mulkrajanops are not of sufficient quality to collect reliable character data; therefore, further analysis of the actual specimen is needed.

‘‘ Microtitan ?’’ elongatus Qi, 1987

HOLOTYPE: IVPP V5767 , a right P3–M3 (M1 and M2 largely broken; M3 preserves only mesostyle and metacone).

TYPE LOCALITY: Daatein Obo, lower beds (Arshanto) of the Irdin Manha Formation, Inner Mongolia.

AGE: Middle Eocene (Irdinmanhan land mammal ‘‘age’’).

DETERMINATION: Nomen dubium: holotype lacks diagnostic features.

REMARKS

The holotype of ‘‘ Microtitan ?’’ elongatus (IVPP V5767), consisting of a partial series of upper cheek teeth is similar to M. mongoliensis , but slightly larger. It was described by Qi (1987) as having well-developed mesostyles on P3 and P4, characteristics that are not seen in M. mongoliensis . The original specimen was not available; Qi’s figure of the type ( Qi, 1987: fig. 44) shows only a small P4 mesostyle, but it is much less developed than typical molar mesostyles. A P3 mesostyle is not evident. Considering that premolar mesostyles occasionally occur in many brontothere species, there is not enough evidence for a distinct species; elongatus potentially fits within a species concept of M. mongoliensis , but the material lacks diagnostic characters of Microtitan . There is evidence for multiple Microtitan -sized brontotheres from the middle Eocene of Asia. For instance, Qi and Beard (1996) referred other brontothere material to Microtitan sp. , but that material, described further below, actually represents a small Metarhinus -like brontothere. Metarhinus fluviatilis , a brontothere from North America, was similar in size to the elongatus specimen. Given the lack of diagnostic features in the holotype of ‘‘ Microtitan ?’’ elongatus, this species is a nomen dubium.