Morphology and function of Neandertal and modern human ear ossicles.
The diminutive middle ear ossicles (malleus, incus, stapes) housed in the tympanic cavity of the temporal bone play an important role in audition. The few known ossicles of Neandertals are distinctly different from those of anatomically modern humans (AMHs), despite the close relationship between both human species. Although not mutually exclusive, these differences may affect hearing capacity or could reflect covariation with the surrounding temporal bone. Until now, detailed comparisons were hampered by the small sample of Neandertal ossicles and the unavailability of methods combining analyses of ossicles with surrounding structures. Here, we present an analysis of the largest sample of Neandertal ossicles to date, including many previously unknown specimens, covering a wide geographic and temporal range. Microcomputed tomography scans and 3D geometric morphometrics were used to quantify shape and functional properties of the ossicles and the tympanic cavity and make comparisons with recent and extinct AMHs as well as African apes. We find striking morphological differences between ossicles of AMHs and Neandertals. Ossicles of both Neandertals and AMHs appear derived compared with the inferred ancestral morphology, albeit in different ways. Brain size increase evolved separately in AMHs and Neandertals, leading to differences in the tympanic cavity and, consequently, the shape and spatial configuration of the ossicles. Despite these different evolutionary trajectories, functional properties of the middle ear of AMHs and Neandertals are largely similar. The relevance of these functionally equivalent solutions is likely to conserve a similar auditory sensitivity level inherited from their last common ancestor.
Department of Human Evolution, Max Planck Institute for Evolutionary Anthropology, 04103 Leipzig, Germany; alexander_stoessel@eva.mpg.de.
Alexander
0000-0003-2434-2542
A
Stoessel
Department of Human Evolution, Max Planck Institute for Evolutionary Anthropology, 04103 Leipzig, Germany.
Romain
R
David
Department of Human Evolution, Max Planck Institute for Evolutionary Anthropology, 04103 Leipzig, Germany.
Philipp
P
Gunz
Department of Otorhinolaryngology, Jena University Hospital, Friedrich-Schiller-University Jena, 07743 Jena, Germany.
Tobias
T
Schmidt
Department of Human Evolution, Max Planck Institute for Evolutionary Anthropology, 04103 Leipzig, Germany; Department of Cell and Developmental Biology, University College London, WC1E 6BT London, United Kingdom.
Fred
F
Spoor
Department of Human Evolution, Max Planck Institute for Evolutionary Anthropology, 04103 Leipzig, Germany.
Jean-Jacques
JJ
Hublin
D000818:Animals; D005075:Biological Evolution; D004429:Ear Ossicles / Q000033:anatomy & histology* / Q000473:pathology*; D004432:Ear, Middle / Q000033:anatomy & histology; D006801:Humans; D007091:Image Processing, Computer-Assisted; D059125:Neanderthals / Q000033:anatomy & histology*; D025341:Principal Component Analysis
3D shape; covariation; homo; middle ear
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