HONING COMPLEX

The morphological basis for terming a fossil a hominid essentially rests on its dentition and the skeletal evidence that would show that it was a biped. Dental evidence has long been used to try to determine evolutionary relationships both because of the prevalence of teeth in the fossil record and because of the marked differences between human dentition and that of chimpanzees, specifically in the human reduction of the canine and the loss of the C/P3 honing complex.

What is Honin complex?

• CP3 honing complex refers to combination of canine and first premolar teeth that forms a self-sharpening apparatus.
• In a monkey or ape, the enormous canines of the upper jaw must fit into a space, or diastema, in the tooth row of the lower jaw (mandible) where they slide past the third premolar.
• They “sharpened” or “honed” them slightly by subtle abrasion against the “third” lower premolar as the mouth opened and closed.
• This is referred to as the “C/P3 honing complex.”

Who had it? Pre-hominid forms and also the modern monkeys

• Evolutionary Significance: Its disappearance is taken by some scholars as representing, jointly with substantial bipedalism, the beginning of the hominid line of descent.
• Loss of the CP3 honing complex is among the first changes in the hominid lineage
• Fossils attributed to Ardipithecus and the earliest species of Austral- opithecus suggest that maxillary canine height reduction took place and the function of canine honing was lost.

Details:

• Based upon early hominin teeth, they were generalists like chimps, likely getting the majority of their carbohydrates and fats from fruit, protein from young leaves, and possibly fat and protein from animal matter, e.g. social insects (chimps and gorillas eat a lot of ants and termites) and animals caught opportunistically.
• No early hominins exhibit the same degree of canine size or sharpness as chimp and gorilla males.
• Their canines stay sharp via a honing (sharpening) action with the first lower premolar, termed a sectorial premolar due to its unicuspid morphology. The combination of the action and morphology of the two teeth is termed a “honing complex”.
• Thus, if the common ancestor of chimps, gorillas, and hominins possessed a premolar honing complex, as seems likely, the early hominin fossil evidence suggests that they were losing their fighting teeth.

Analysis: If a fossil specimen is male, that would certainly make the lack of a honing canine significant, however, the thickness of the mandibular corpus can be functionally related to increasing the power of the masticatory apparatus, as in robust australopithecines. This might also correlate with the extensive canine wear, as certain other Miocene apes such as Gigantopithecus show this same pattern and lack of honing complex. If the specimen were a female ape such as Ramapithecus, it might also explain the lack of a honing complex. While the lack of a canine honing complex can suggest hominid status, it is by no means beyond question.