Ectopic maxillary third molar in Early Pleistocene Homo antecessor from Atapuerca-Gran Dolina site (Burgos, Spain)

Here we describe the case of an ectopic maxillary third molar (M³ ), preventing the eruption of the M² , in the individual H3 of the hominin hypodigm of level TD6.2 of the Early Pleistocene site of Gran Dolina (Sierra de Atapuerca, Spain).

The fossil remains from the TD6.2 level of the Gran Dolina site (about 170 specimens) are assigned to Homo antecessor. Different geochronological methods place these hominins in the oxygen isotopic stage 21, between 0.8 and 0.85 million years ago (Ma). The immature individual H3 is represented by an almost complete midface (ATD6-69), preserving various teeth in situ. We used high-resolution microtomograhy (mCT) to investigate the abnormal position of the left M³ , virtually reconstruct M² , and M³ as well as assessing the development stage of these. Finally, we compare this case with extinct and extant populations.

Based on the identified signs, we suggest that individual H3 suffered from a unilateral impaction of the M² as a result of the ectopic position of the developing M³ .

We conclude that the most likely etiology for the ectopic position of the M³ is the lack of space in the maxilla. We discuss possible contributing factors, such as morphometric aspects of the maxilla and the early mineralization of the M³ , to support the M² impaction. Finally, due to the early age at death of this individual we did not identify any secondary lesion associated with the M² impaction.