Occurrence of neanderthal features in mandibles from the Atapuerca-SH site

Analysis of variation and distribution of evolutionary novelties is meaning ful in understanding evolutionary processes. The mandible, as a morphologic al complex, comprises a large number of derived Neanderthal features. The p resent study investigates whether the features usually considered as Europe an lineage apomorphies evolved independently; the occurrence of these featu res is studied in the mandibles from the Sima de los Huesos (SH) site (Atap uerca, Spain). For comparative purposes, a large sample of Neanderthal mand ibles as well as older fossil Home specimens have been used for the study. Chi-square tests were employed to test for independence. The SH mandibles p resent a set of features that clearly show the basic architecture of the Ne anderthal mandible. A highly significant association is detected in the var iation of the position of the mental foramen, the lateral prominence, and t he anterior marginal tubercle, as well as in the development of retromolar space. However, a much weaker association is detected in the features of th e internal aspect of the mandible, with a few exceptions. Features of the e xternal aspect of the mandible occur chronologically earlier than those obs erved in the internal aspect. The hypothesis that two distinct and consecut ive morphological processes have driven the emergence of the European linea ge throughout the Middle Pleistocene is proposed. A first transformation af fects the mandible by means of backwards displacement of the structures loc ated at the external aspect, as well as the position of the condyle. A seco nd process would modify the features of the internal aspect of the mandible , in which the relief of the masseteric and pterygoid fossae are affected, in association with a spatial rearrangement of the corpus and ramus. Analyz ed individually, some of the considered features may be questioned as Neand erthal apomorphies (Trinkaus,l993; Franciscus and Trinkaus, 995); however, the joint occurrence of many of them suggests that the complex is an evolut ionary novelty. (C) 2001 Wiley-Liss, Inc.