Contributed by Juan Luis Arsuaga, July 29, 2015 (sent for review May 20, 2015; reviewed by Trenton W. Holliday and Christopher B. Ruff)
The middle Pleistocene Sima de los Huesos (SH) fossil collection provides the rare opportunity to thoroughly characterize the postcranial skeleton in a fossil population, comparable only to that obtained in the study of the Neandertal hypodigm and recent (and fossil) modern humans. The SH paleodeme can be characterized as relatively tall, wide, and muscular individuals, who are less encephalized than both Neandertals and modern humans. Some (but not all) Neandertal derived traits are present, which phylogenetically links this population with Neandertals. Thus, the full suite of Neandertal features did not arise all at once, and the evolution of the postcranial skeleton could be characterized as following a mosaic pattern.
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.
Author contributions: J.L.A., J.M.B.d.C., and E.C. codirected the Atapuerca excavations and research project; J.L.A. designed research; J.L.A., J.-M.C., C.L., A.G.-O., A.P., L.R., R.G.-G., A.B., R.M.Q., A.P.-P., I.M., A.A., A.G.-T., E.P.-R., N.S., N.G., A.A.d.V., G.C.-B., J.M.B.d.C., and E.C. performed research; J.L.A., J.-M.C., C.L., A.G.-O., A.P., L.R., R.G.-G., A.B., R.M.Q., A.P.-P., I.M., A.A., A.G.-T., E.P.-R., N.S., N.G., A.A.d.V., and G.C.-B. analyzed data; and J.L.A., J.-M.C., C.L., A.G.-O., A.P., L.R., R.G.-G., A.B., R.M.Q., A.P.-P., and I.M. wrote the paper.
Reviewers: T.W.H., Tulane University; and C.B.R., The Johns Hopkins University School of Medicine.
The authors declare no conflict of interest.
This article contains supporting information online at www.pnas.org/lookup/suppl/doi:10.1073/pnas.1514828112/-/DCSupplemental.
Freely available online through the PNAS open access option.
