Crown size and cusp proportions in Homo antecessor upper first molars. A comment on Quam et al. 2009

Abstract

A recent evaluation of upper first molar (M¹) crown size and cusp proportions in the genus Homo (Quam et al. 2009) describes Homo antecessor as maintaining a primitive pattern of cusp proportions, similar to that identified in australopithecines and the earliest members of the genus Homo. These results contrast with those of Gómez-Robles et al. (2007), who described the crown shape in these molars as derived and similar to Neanderthals and European Homo heidelbergensis. The reassessment of these measurements following the same methodology described by Quam et al. (2009) in all the M(1) s that are currently part of the hypodigm of H. antecessor demonstrates that the fossils from TD6 not only have the same cusp proportions identified in later Homo species, but also a strongly reduced metacone and a large hypocone shared with Middle and Upper Pleistocene members of the Neanderthal lineage. The evolutionary significance of these features should be evaluated in light of the results provided by recently discovered dental, cranial, mandibular, and postcranial H. antecessor fossils.

Fig. 1

Right upper first molar ATD6-103 showing the separation of the different cusp base areas (Pr: protocone; Pa: paracone; Me: metacone; Hy: hypocone), the occlusal polygon (shaded polygon) and the angles located at each cusp (angles of the occlusal polygon). Scale bar: 1 cm. Buccal: top part of the image; lingual: bottom; mesial: right; distal: left.

Fig. 2

Homo antecessor upper first molars. Right half of the figure: photographs of the molars showing the cusp division used to obtain the measurements in Table 1. From top to bottom: ATD6-10: right antimere of individual H1 (incorrectly referred to as ATD6-18 in Table 1 of Gómez-Robles et al. 2007); ATD6-11: left antimere of individual H1; ATD6-69: right antimere of individual H3; ATD6-69: left antimere of individual H3; ATD6-103: right antimere (the only preserved one) of individual H5. Scale bars: 1 cm. Buccal: top; lingual: bottom. Right antimeres: mesial – right, distal – left. Left antimeres: mesial – left, distal – right. The small cusp located between the metacone and the hypocone in the molars of ATD6-69 is the metaconule, or c5.