Journal of Human Evolution最新文献

The bony labyrinth of the inner ear houses the sensory end-organs responsible for balance (otolithic system in the utricle and saccule, and semicircular canal system) and hearing (cochlea). Study of the bony labyrinth has revealed considerable morphological diversity in the hominin lineage (semicircular canals and cochleae) and aided in reconstructing essential aspects of primate evolution, including positional behavior, audition, and phylogenic affinities. However, evidence of evolutionary change in the hominin otolithic system remains elusive. Such morphological variation in these gravitoinertial sensory end-organs may suggest functional differences as their geometry is linked with positional behavior. We approach the question of evolutionary morphological change in the hominin otolithic system by examining bony vestibule morphology in two South African hominin taxa Paranthropus robustus (n = 9) and Australopithecus africanus (n = 6), compared to extant hominids (Pongo pygmaeus, Gorilla gorilla, Pan troglodytes, and Homo sapiens). We use landmark-based shape analyses of 78 extant hominid inner ears by means of virtual three-dimensional models derived from micro-computed tomography scans. Thirty bony landmarks were chosen to approximate otolithic organ morphology and relative configuration. Results show a distinctive morphology in P. robustus compared to A. africanus and extant hominids. Specifically, P. robustus exhibits anterolateral-posteromedial compression in bony otolithic organ structure, reducing the size of the saccule and vestibular aqueduct. In contrast, A. africanus exhibits a modern-human-like otolithic system. This newfound morphological diversity identifies unique bony features of the P. robustus inner ear which: 1) offers potential evidence for differential positional behavior between P. robustus and A. africanus and 2) presents osteological markers to be used in taxonomic identification of P. robustus remains and in future assessments of Paranthropus classification.

The study of the ribcage is fundamental to understanding hominin evolution. However, ribs and vertebrae are scarce in the fossil record. Although Neanderthals are one of the most represented and, therefore, one of the most studied fossil Homo species, it is controversial whether there is a standardized Neanderthal ribcage morphotype that could differ from modern humans. Hence, we used three-dimensional geometric morphometrics to reconstruct and compare the Neanderthal ribcage of Shanidar 3 with another Neanderthal specimen, Kebara 2, and with 58 Homo sapiens individuals of worldwide distribution. Shape differences among the Neanderthal and H. sapiens ribcages were analyzed by a hierarchical cluster using the Euclidean distances among the permuted Procrustes distances between groups. Size differences between the Neanderthal and H. sapiens ribcages were examined using a permutation test on centroid size. To examine the potential for allometry, we performed a linear regression of Procrustes coordinates on centroid size of the sample, followed by a principal component analysis in form space. Our results show that Shanidar 3 has the 'bell-shaped' thorax typically described for Neanderthals. In fact, the shapes of both Shanidar 3 and Kebara 2 ribcages cluster apart from that of H. sapiens, being closer to cold-adapted individuals. The study of the centroid size supports similarities between Neanderthals and cold-adapted H. sapiens since significant size differences were found only between Neanderthals and temperate/tropical recent humans. The linear regression and principal component analysis showed an allometric relationship between ribcage size and shape, suggesting Neanderthals had larger and stockier ribcages than most H. sapiens, although they fall within the H. sapiens range of variation. Finally, ribcage similarities found between Shanidar 3 and Kebara 2, both inhabiting warm Levantine locations during the Upper Pleistocene, could challenge the conventional idea of a cold-adapted bauplan in Neanderthals.