Four separate species of Hydaspitherium were described more than a century ago, but Bhatti, Khan & Akhtar 2012 concluded that their differences can be explained as sexual dimorphism and intraspecific variability: H. birmanicum (Pilgrim 1910) is based on a single right upper molar. H. grande (Lydekker 1878) and H. magnum (Pilgrim 1910) are only slightly larger than H. megacephalum and the variation in dentition does not support separate taxa. Bhatti et al. 2012 accepted two species in the Siwaliks: the smaller H. megacephalum and the larger H. grande until more material has been collected.[6]
Lydekker, R. (1878). "Indian tertiary and post-tertiary vertebrate. 3. Crania of ruminants". Palæontologia Indica. Memoirs of the Geological Survey of India. 10. 1 (3): 88–181. OCLC20842760.
Pilgrim, G. E. (1910). "Notices of new mammalian genera and species from the Tertiaries of India". Records of the Geological Survey of India. 40 (1): 63–71.