Forster-Cooper (1934) revised the extinct rhinoceroses known in the Dera Bugti area. Of the fossils he discussed, the specimens assigned to Rhinoceros blandfordi, including the partial palate NHM 15365, show the closest affinities to the teeth from localities Z143 and Z147 of the Chitarwata Formation.
Zinda Pir rhinoceros teeth were compared to those from Kumbhi at Dera Bugti
described and assigned to Rhinoceros blandfordi by
Forster-Cooper (1934;
plate 67, figures 34 and 36).
Shared features
are a quadrate premolar with slight crista, molars with constricted protocone,
large antecrochet, and accessory cuspules between the protocone and hypocone.
However, as Forster-Cooper (1934, p. 593) pointed out, “such characters as a
strongly constricted protocone, a large anterocrochet, a cingulum, etc., are
features too widely spread to afford any safe guide to generic distinction.”
The Zinda Pir rhinoceros differs from the Bugti Rhinoceros blandfordi having
a cingulum restricted in position and extent, a small or absent metastyle in M2
and probably M3 (based on Z2269C), and two small rounded crochets on the
metaloph resulting in a more sinuous shaped lingual valley. The Zinda Pir
rhinoceros M3 is also larger than the Bugti Hills Rhinoceros blandfordi
approaching the size range of smaller Paraceratherium (Figure 4).
The phylogenetic analysis of the rhinocerotids by Antoine et al. 2003b provides a paradigm to evaluate the phylogenetic assignment of the Z143/Z147 rhinoceros based on its preserved dental and maxillary characteristics. That analysis proposed that the: 1) Aceratheriina are united by an indentation of the metaloph (i.e., postfossette) on the P2-4 and an “irregular” origination of the zygomatic process on the maxillary, 2) the Teleoceratina (excluding Brachypotherium) are united with the base of the anterior zygomatic process positioned low and the antecrochet always present on the upper molars, and 3) the Rhinocerotina are united by cheek teeth with cement present, lingual cingula on P2-4 reduced to a knob, and absence of the labial cingula on upper molars.
A comparison of the distribution of these synapomorphic dental and cranial character states of the Rhinocerotinae against those of the Z143/Z147 rhinoceros indicates a mixture of features from the Aceratheriina, Teleoceratina, and Rhinocerotina as summarized in Table 2. For example, the indentation of the premolar metaloph combined with the maxillary features of regular origination and a “high” position for the zygomatic process is consistent with the Aceratheriina. The Rhinocerotina also show a high position of the zygomatic process, but in the analysis by Antoine et al. (2003b), only Brachypotherium displays that condition in the Teleoceratina. The presence of a pronounced antecrochet on all of the molars is consistent with the Teleoceratina. Affinity to the Rhinocerotina is suggested by the reduction of a lingual cingulum on the premolar to a knob (i.e., the spade-shaped accessory cuspule), absence of the labial cingulum on upper molars, and incipient cement on the cheek teeth. As a whole, the fossil teeth and partial maxilla from the upper unit of the Chitarwata Formation do not display synapomorphies that persuasively place this rhinoceros into one of known early Miocene subtribes or genera on the Indian subcontinent.
It should be observed that although Forster-Cooper (1934) considered the constriction of the protocone a plesiomorphic character, and this is generally supported in the analysis by Antoine et al. 2003b, the degree of protocone constriction observed on the Z143 and Z147 specimens (e.g., M3 and M1) is not ubiquitous among the rhinoceros genera of the Oligocene and early Miocene of Dera Bugti. This pronounced protocone constriction is observed for Rhinoceros blandfordi, as well as the small Elasmotherine Bugtirhinus (Antoine and Welcomme 2000). It is prevalent in the Teleoceratina clade (e.g., Teleoceras) but is not present (Antoine et al. 2003b, character 116) in Brachytherium and Aprotodon. Thus, while this feature does not support a particular Bugti Hills candidate for assignment, it may broadly suggest a closer evolutionary affinity of the Zinda Pir form to Rhinoceros blandfordi. Also notable, the structure of the metacone-metastyle portion of the metaloph is broad on the Zinda Pir M2 and similar to that of Aceratherium incisivum and Brachypotherium.
