Three important fossil hominids were found in July 1992 in the Middle Pleistocene cave site called Sima de los Huesos (Sierra de Atapuerca, Burgos, Northern Spain). One is a complete calvaria (cranium 4), the second a virtually complete cranium (cranium 5), the third represents a more fragmentary cranium of an immature individual (cranium 6). There is a large difference in size between the two adult specimens (for example endocranial volume 1,125 cm3 versus 1,390 cm3). The Atapuerca human remains are dated to > 300,000 years. The Atapuerca cranial sample fits within the 'archaic Homo sapiens' group, but is well differentiated from the Asian Homo erectus group. The extensive Atapuerca human collection is the most complete sample of Middle Pleistocene humans yet discovered from one site, and appears to document an early stage in Neanderthal evolution.

Current knowledge of the evolution of the postcranial skeleton in the genus Homo is hampered by a geographically and chronologically scattered fossil record. Here we present a complete characterization of the postcranium of the middle Pleistocene paleodeme from the Sima de los Huesos (SH) and its paleobiological implications. The SH hominins show the following: (i) wide bodies, a plesiomorphic character in the genus Homo inherited from their early hominin ancestors; (ii) statures that can be found in modern human middle-latitude populations that first appeared 1.6-1.5 Mya; and (iii) large femoral heads in some individuals, a trait that first appeared during the middle Pleistocene in Africa and Europe. The intrapopulational size variation in SH shows that the level of dimorphism was similar to modern humans (MH), but the SH hominins were less encephalized than Neandertals. SH shares many postcranial anatomical features with Neandertals. Although most of these features appear to be either plesiomorphic retentions or are of uncertain phylogenetic polarity, a few represent Neandertal apomorphies. Nevertheless, the full suite of Neandertal-derived features is not yet present in the SH population. The postcranial evidence is consistent with the hypothesis based on the cranial morphology that the SH hominins are a sister group to the later Neandertals. Comparison of the SH postcranial skeleton to other hominins suggests that the evolution of the postcranium occurred in a mosaic mode, both at a general and at a detailed level.human evolution | bauplan | postcranial anatomy |

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