Alejandro Bonmatí

Neandertal roots: Cranial and chronological evidence from Sima de los Huesos

Neandertal ancestors from Pleistocene Spain The Sima de los Huesos site in Atapuerca, northern Spain, is a rich source of fossil hominin specimens. The site has now yielded further skull specimens that illuminate patterns of human evolution in Europe nearly half a million years ago. Arsuaga et al. studied 17 crania, including 7 that are new specimens and 6 that are more complete than before (see the Perspective by Hublin). This assemblage of specimens reveals the cranial, facial, and dental features of the Atapuerca hominins, which allows more precise evolutionary positioning of these Neandertal ancestors. Science, this issue p. 1358; see also p. 1338 Seventeen skulls from at least 430 thousand years ago illuminate hominin evolutionary patterns in Pleistocene Europe. [Also see Perspective by Hublin] Seventeen Middle Pleistocene crania from the Sima de los Huesos site (Atapuerca, Spain) are analyzed, including seven new specimens. This sample makes it possible to thoroughly characterize a Middle Pleistocene hominin paleodeme and to address hypotheses about the origin and evolution of the Neandertals. Using a variety of techniques, the hominin-bearing layer could be reassigned to a period around 430,000 years ago. The sample shows a consistent morphological pattern with derived Neandertal features present in the face and anterior vault, many of which are related to the masticatory apparatus. This suggests that facial modification was the first step in the evolution of the Neandertal lineage, pointing to a mosaic pattern of evolution, with different anatomical and functional modules evolving at different rates.

Middle Pleistocene lower back and pelvis from an aged human individual from the Sima de los Huesos site, Spain

We report a nearly complete lumbar spine from the Middle Pleistocene site of the Sima de los Huesos (SH) that is assigned to the previously published SH male Pelvis 1 [Arsuaga JL, et al. (1999). Nature 399: 255–258]. The “SH Pelvis 1 individual” is a unique nearly complete lumbo-pelvic complex from the human Middle Pleistocene fossil record, and offers a rare glimpse into the anatomy and past lifeways of Homo heidelbergensis. A revised reconstruction of Pelvis 1, together with the current fossil evidence, confirms our previous hypothesis that the morphology of this pelvis represents the primitive pattern within the genus Homo. Here we argue that this primitive pattern is also characterized by sexual dimorphism in the pelvic canal shape, implying complicated deliveries. In addition, this individual shows signs of lumbar kyphotic deformity, spondylolisthesis, and Baastrup disease. This suite of lesions would have postural consequences and was most likely painful. As a result, the individual’s daily physical activities would have been restricted to some extent. Reexamination of the age-at-death agrees with this individual being over 45 y old, relying on the modern human pattern of changes of the articular surfaces of the os coxae. The presence of degenerative pathological lesions and the advanced age-at-death of this individual make it the most ancient postcranial evidence of an aged individual in the human fossil record. Additional nonpathological SH lumbo-pelvic remains are consistent with previous hypotheses, suggesting a less-pronounced sagittal spinal curvature in Neandertals compared with Homo sapiens.

Postcranial morphology of the middle Pleistocene humans from Sima de los Huesos, Spain

Significance 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.

Early hominin auditory capacities

Hearing in early hominins may have facilitated an increased emphasis on short-range vocal communication in open habitats. Studies of sensory capacities in past life forms have offered new insights into their adaptations and lifeways. Audition is particularly amenable to study in fossils because it is strongly related to physical properties that can be approached through their skeletal structures. We have studied the anatomy of the outer and middle ear in the early hominin taxa Australopithecus africanus and Paranthropus robustus and estimated their auditory capacities. Compared with chimpanzees, the early hominin taxa are derived toward modern humans in their slightly shorter and wider external auditory canal, smaller tympanic membrane, and lower malleus/incus lever ratio, but they remain primitive in the small size of their stapes footplate. Compared with chimpanzees, both early hominin taxa show a heightened sensitivity to frequencies between 1.5 and 3.5 kHz and an occupied band of maximum sensitivity that is shifted toward slightly higher frequencies. The results have implications for sensory ecology and communication, and suggest that the early hominin auditory pattern may have facilitated an increased emphasis on short-range vocal communication in open habitats.

Revisiting the developmental stage and age-at-death of the "Mrs. Ples" (Sts 5) and Sts 14 specimens from Sterkfontein (South Africa): do they belong to the same individual?

During the 1947 fieldwork season, Member 4 (2‐3 My) of the South African Sterkfontein site yielded two important Australopithecus africanus fossils: a cranium popularly nicknamed “Mrs. Ples” (Sts 5), and a partial skeleton (Sts 14). Previous reports have proposed that Sts 5 was a nonfully grown adolescent individual (Thackeray et al., S Afr J Sci 2002a;98:21–22), and that Sts 14 was a sub‐adult specimen (according to various signs of immaturity in the skeleton) (Berge and Gommery, C R Acad Sci Paris, Sciences de la terre et des planètes 1999;329:227–232; Häusler and Berger, J Hum Evol, 2001;40:411–417; Thackeray et al., S Afr J Sci, 2002b;98:211–212). It was subsequently proposed that these fossils actually belonged to the same individual (Thackeray et al., S Afr J Sci, 2002b;98:211–212), a proposition supported by their spatial positions within the site. The present work attempts to revise these different assertions. The results obtained: (i) show that the Sts 5 fossil represents a fully grown adult cranium; (ii) provide new evidence of immaturity in the Sts 14 skeletal elements (sustaining the proposed young adult age of this specimen), and (iii) suggest that although the revised ages‐at‐death for these fossils are partially compatible, there is no evidence to support the idea that they represent a single individual. Finally, the encephalization quotient associated with a hypothetical union of Sts 5 and Sts 14 (calculated using data from both specimens) lies between the upper and lower limits of the currently estimated range for this species and H. habilis, respectively. Anat Rec, 2008.