Apes and apomorphies: the anterior nasal spine as a projection of cladistic conceptions.

Projections, tubercles, or spines of bone at the anterior margin of the piriform aperture occur in widely varying forms among catarrhine primates. This paper describes, illustrates, and tabulates the frequencies of such structures by age and sex in a large collection of Pan troglodytes verus skulls. In the overall sample of 263 skulls where the region could be observed, these protuberances of bone occur bilaterally in 10.7% of specimens and unilaterally in an additional 3.4%. They increase in frequency with age to a high of 16.9% in adult and older animals. Among adult specimens, these projections of bone in the anterior nasal region are present more commonly in females than in males. In a comparative context, variants on this structure in nonhuman primates, some of them documented previously, should help to counter the cladistic conception that the anterior nasal spine is an apomorphic or evolutionary novel morphological structure in hominids.