Beginning with some of the earliest discoveries of hominoid (ape) fossils in the Miocene Siwalik Sequence of Pakistan and India, a number of upper canine teeth with an atypical morphology and wear pattern (for apes) have been assigned to the late Miocene hominoid genus Sivapithecus. None of these specimens was associated with other Sivapithecus dental remains. Also recovered during this period were a number of canines with a very different morphology and wear pattern, some of which were still in place in Sivapithecus jaws, including the type specimen of S. sivalensis. Their identity was therefore unambiguous. Most workers who collected and described the atypical canines commented on the unusual morphology, but no one appears to have entertained the possibility that these canines might belong to some other kind of mammal.
The atypical canines figured prominently in taxonomic revisions of Sivapithecus during the 1970s and 1980s and in attempts to characterize canine sexual dimorphism in Sivapithecus. Since all of these canines came from the Chinji Formation, whereas all those of more typical morphology were (incorrectly) thought to come from younger sediments, I proposed in 1986 that Sivapithecus included time-successive species, which could be diagnosed by canine morphology.
Based on my subsequent work on canine morphology and sexual dimorphism in living and fossil apes, I eventually began to doubt that the atypical canines were hominoid. These suspicions were particularly aroused by the unusual wear pattern on these canines, which I did not observe in any other anthropoid species – the complete lack of a distal (posterior) wear facet resulting from contact with the lower anterior premolar, even in canines with heavy mesial (anterior) wear. In all anthropoid species, the upper canines begin to develop a distal wear facet immediately upon coming into occlusion with the lower teeth. Subsequent comparison of the atypical canines with those of other fossil mammals revealed them to be the canines of female pigs, probably Listriodon pentapotamiae.
The notion of time-successive species of Sivapithecus in the Siwaliks cannot, therefore, be supported by canine morphology. With the removal of the misidentified canines, an earlier characterization of Sivapithecus as having little canine sexual dimorphism is also incorrect. These findings alter our views about the evolution and paleobiology of Sivapithecus.