Fossil profile: Krapina 49 maxilla

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Shovel-shaped incisors are a striking anatomical variant in many living people. The upper incisors of most people are gently curved or straight across, and the side nearest the tongue is shares this same gentle curvature. But in some people, the edges of the tooth have a strong ridge extending back toward the tongue, defining the edges of the incisor like a coal shovel. Hence the term, “shovel-shaped”. This trait varies in different regions of the world, being more common in eastern Asia and the Americas, although it can be found many other places as well.

Krapina 49 maxilla

Similar incisor traits evolved within several populations of ancient human relatives. The best known of these is the shovel-shaped appearance of many Neandertal incisors. My illustration here of the Krapina 49 maxilla shows one of the clearest examples, with both central and lateral incisors showing the shoveled form. But in Neandertals the shape is a bit different from in some living populations, with strong curvature across the entire tooth crown, so that the ridges are more like a wooden flour scoop than a coal shovel.

For a morphologist, a difference in form often suggests a difference in origin. Today we know that a strong genetic influence on shovel-shaping in living people is a variant of the EDAR gene. It does not explain all the variance, but it consistently comes up as a strong genetic correlation. That variant is a new mutation in recent people, and was strongly selected across some of the last 35,000 years or so. We do not know the genetic basis of the shoveled morphology in Neandertals, but it seems to have evolved convergently with that in recent people.

Like most skeletal and dental traits that we recognize in Neandertals, this one varied within that ancient population. Some Neandertal individuals had profoundly shovel-shaped incisors, while others were less extreme or lacked them entirely. One idea to explain why this ancient population evolved toward incisor robustness is that stronger incisors with larger incisive surfaces helped to adapt them to cultures in which they habitually used their anterior teeth as a third hand, to grip objects, process hides, or to peel tough skins from plant foods. Several older Neandertal individuals have extreme wear on these front teeth. In a few, the wear takes on a distinctly beveled shape, angled outward in a way that was not likely the result of chewing foods.