SYSTEMATIC PALEONTOLOGY

Family Rhinocerotidae Owen 1845
Subfamily Rhinocerotinae Owen 1845
Tribe Rhinocerotini Owen 1845
Subtribe incertae sedis
Indeterminate Genus and Species

MATERIAL

Fossils were collected in January 2000, from the upper unit of the Chitarwata Formation at Zinda Pir Dome near the village of Dalana. The Pakistan Museum of Natural History (PMNH) is the repository for the specimens, which are designated Z2269A, left P2; Z2269B, right M2; Z2269C, right M3 with fractured and dislocated partial maxilla; Z2269D, left M3; Z2268, right M1 (Figure 2, Figure 3). Z2269 specimens are from locality Z143, and specimen Z2268 is from locality Z147. Specimens of Paraceratherium and Rhinoceros blandfordi addressed herein are from the collections at the Natural History Museum of London (NHM).

METHODS

Classification designation of the Rhinocerotinae follows the phylogenetic analysis by Antoine et al. 2003b, and perissodactyl dental terminology generally follows Hooker 1989. Dental orientations follow the conventions of Smith and Dodson (2003). Measurements of Chitarwata Formation rhinocerotid teeth (mm) are provided in Table 1.

DESCRIPTION

The teeth are moderately hypsodont with minor cement (as observed on chipped Z2269B), large sized, and moderately worn. All but the P2 have incomplete crowns. The molars display prominent accessory cuspules between the protocone and hypocone, large antecrochets, and narrow preprotocrista. Prominent cingula are restricted to the mesial tooth edge near the protocone on the molars.

P2: The tooth (Z2269A, left P2) is roughly quadrate but narrows mesially with the metaloph longer than the protoloph. The buccal enamel is thick (4.9 mm), and lingual edge enamel is thin (2.0 mm). The buccal side of the tooth has two shallow grooves producing a trilobed buccal occlusal outline. A narrow cingulum is present along the mesial side of the protocone, narrowing on the lingual side of the protocone, broadened into a spade-shaped accessory cuspule (sensu Hanson 1989) between the protocone and hypocone, and ascending towards the hypocone. A strong protocone-hypocone connection is present at this state of wear. A small elliptical prefossette is present with its axis directed parallel to the buccal edge of the tooth. A large heart-shaped postfossette is also present. The crista is small and projects into the lingual valley. The lingual valley between the protoloph and the metaloph is deep, isolated, and Y-shaped. The preparacrista is thin (2.7 mm) as is the preparaconule crista (3.2 mm). The metaloph has a relatively uniform thickness displaying a slight increase in breadth from the neoformed crest (4.0 mm) to the prehypocrista (4.7 mm).

M1: The tooth (Z2268, right M1) is roughly quadrate, and the enamel is thin (1.6 mm). At this state of wear, the mesial portion of the ectoloph (parastyle-preparacrista-paracone) is raised high (17.2 mm) above the level of the rest of the metaloph and protoloph. The parastyle projects beyond (4.8 mm) the mesial edge of the tooth. The protocone is conical with a narrow preprotocrista producing a “constricted protocone” condition. There is a broad cingulum originating low on the mesial side of the protocone and ascending and joining with the metaloph across from the antecrochet. The antecrochet is large, extends beyond the distal limit of the protocone, and is directed toward the hypocone. The protoloph and the metaloph are roughly parallel. There are two small rounded crochets on the metaloph (here designated as crochet 1 = buccal side of metaloph; crochet 2 = lingual side of metaloph) There is a large (9.0 mm) spade-shaped accessory cuspule between the protocone and hypocone, and it connects low on its buccal side to the antecrochet and crochet 2. The resulting lingual valley is sinuous and open. This tooth is consistent in several ways with the Z2269B M2 from locality Z147 (described below) including: constricted protocone, large antecrochet extending beyond the distal limit of the protocone, large spade-shaped accessory cuspule, sinuous lingual valley, and proportional tooth size. Hence, although it comes from older strata, this M1 is provisionally linked to the same indeterminate genus.

M2: The tooth (Z2269B, right M2) is roughly quadrate, and the enamel is thin (2.0 mm). At this wear stage the ectoloph height is approximately the same as the metaloph and protoloph. The parastyle projects well beyond (8.4 mm) the mesial edge of the tooth and has a “fold” on the buccal edge. The antecrochet is large, extends beyond the distal limit of the protocone, and is directed towards the postfossette. There is a large (8.2 mm) spade-shaped accessory cuspule between the protocone and hypocone, and it connects low on its buccal side to the crochet 2. The resulting lingual valley is sinuous and open.

M3: The teeth (Z2269C, right M3 with partial maxilla; Z2269D left M3) are triangular, but with an enlarged talon, and the enamel is moderate in thickness (3.0 mm). At this state of wear, the metaloph is beveled downwards making it lower than the protoloph. The protocone is conical and buccolingually compressed. The protoloph narrows at the preprotocrista producing a “constricted protocone” condition. The antecrochet is moderate in size and extends beyond the distal limit of the protocone. There is a broad cingulum originating low on the mesial side of the protocone and ascending and joining with the metaloph in alignment with the buccal limit of the lingual valley. There is a thin short cingulum on the distal edge of the tooth below the hypocone. A prominent T-shaped accessory cuspule is situated between the protocone and hypocone. The crochet is well developed, and the lingual valley is open.

Maxilla: A small portion of the right maxilla (Z2269C) and zygomatic arch is preserved including: part of the aveolar region for the M2, the groove between the jugal and maxillary, and about 140.0 mm of the anterior jugal. Despite some missing bone, the base of the anterior portion of the zygomatic arch appears to be high. Anchored by matrix to this portion of the maxilla, but dislocated during original preservation, the M3 and a fragment of the maxilla (or palatine) comprising a small portion of the orbit are preserved.