School of Human Evolution and Social Change, Institute of Human Origins, Arizona State University
Saturday All day, Plaza Level
Supernumerary molars (M4) are an uncommon variant of hyperdontia in primates. Estimates of M4 frequencies in nonhuman anthropoid samples typically range from 0-4% but to greater than 10% in some large-bodied hominoids (e.g., Pongo). In humans the etiology of supernumerary molars remains an open question in non-syndromic cases, in which the most common form of hyperdontia involves multiple occurrences of extra successional teeth, the incisors or premolars.
A.L. 1901-1 is a fragmented mandibular corpus diagnostic of Australopithecus afarensis from Hadar, Ethiopia. The specimen was found on an exposed surface of DD-3 submember sediments of the Hadar Formation and is 3.20 to 3.24 million years old. It retains most of the tooth crowns or roots, and though many of the crowns are heavily eroded or broken, bilateral supernumerary M4s are present as distomolars. The M4s are asymmetrically developed; the left is a fully formed “normal” crown, whereas the right is peg-shaped. Eruption of the left tooth caused severe crowding and rotation of the ipsilateral M3. No such rotation is observed on the right side.
Within the Hadar sample of A. afarensis mandibles containing a complete molar row, 2 out of 21 (9.5%) specimens hold supernumerary M4s. Although the sample size is modest, this frequency is consistent with those reported for large-bodied extant hominoids. Given that both Hadar mandibles bear supernumerary teeth in the most posterior (non-successional) portion of an otherwise normal-appearing tooth row, they are more likely due to anomalous hyperactivity of the dental lamina than to some undiagnosed genetic syndrome.