No abstract

The middle ear ossicles are only rarely preserved in fossil hominins. Here, we report the discovery of a complete ossicular chain (malleus, incus, and stapes) of Paranthropus robustus as well as additional ear ossicles from Australopithecus africanus. The malleus in both early hominin taxa is clearly human-like in the proportions of the manubrium and corpus, whereas the incus and stapes resemble African and Asian great apes more closely. A deep phylogenetic origin is proposed for the derived malleus morphology, and this may represent one of the earliest human-like features to appear in the fossil record. The anatomical differences found in the early hominin incus and stapes, along with other aspects of the outer, middle, and inner ear, are consistent with the suggestion of different auditory capacities in these early hominin taxa compared with modern humans.T he middle ear ossicles have historically played a prominent role in paleontological studies because the appearance of the three bone ossicular chain is considered a defining feature of the emergence of mammals (1, 2). The evolutionary transformation of the malleus and incus, which once formed part of the lower jaw, represents a profound modification of both the feeding and auditory apparatuses and had important implications for the sensory ecology of early mammals (3), including primates (4). However, surprisingly little is known of the auditory ossicles in our early human ancestors because they are among the rarest hominin fossils recovered (5-11). Nevertheless, their study holds great potential as an avenue of inquiry into the evolutionary relationships among fossil taxa, as well as aspects of their sensory perception.In humans, the embryological origins of each of the three ear bones have been thoroughly studied. These tiny bones are fully formed at birth (12, 13) and, unlike other bones of the skeleton, generally do not remodel after about the first year of life (14). The ear ossicles then, in some ways, remain "relic" embryonic bones throughout life, and their evolutionarily conservative nature makes them particularly suitable for phylogenetic analysis (15)(16)(17). Comparative genomic studies have revealed changes during the course of our evolutionary history in several genes related to the development of the auditory structures (18) and hearing (19), and previous studies of the inner ear in early hominins have provided insights into their taxonomic relationships and locomotion (20).A few anatomical differences in the ear ossicles of fossil hominins have been reported previously (6-11). Among early hominins, the incus in Paranthropus robustus (SK 848) was argued to show a highly derived articular facet morphology, revealing profound differences from living hominids (7, 21). In contrast, the stapes of Australopithecus africanus (Stw 151) appears similar to African apes in showing generally small metric dimensions, including the size of the footplate (8). We report here on a complete right ossicular chain (malleus, incus, and stapes) (Table 1) that was ...

No abstract

In spite of the importance of auditory ossicles in anthropological studies, very little attention has been paid to these bones, which are only rarely recovered in archaeological excavations and in osteological collections. In this paper, we attempt to review some studies that started in the 1960 from when we first collected and prepared ossicles from the early Egyptian osteological collection of Giovanni Marro in Turin (Italy). We attempt to delineate the potential of ear bones in the study of man. In a few cases, archaeological ossicles were discussed in connection with some forms of pathology. Other studies examined the phylogeny of primates based on auditory ossicles. The function of the ossicles is to transmit sound waves to the cochlear endolymph. The energy transmitted through the ossicles is conserved by the action of two levers, which convert the relatively wide and low-energy movements of the hammer into smaller high-energy movements of the stirrup. It is a matter of argument whether the different proportions of the ossicles may imply variations in auditory perception in primates, including man. While the hammer of modern humans and that of the great apes show similar absolute sizes, nevertheless, the ape manubrium is appreciably greater than that of man. This difference, combined with stirrup proportions, causes a strong "low-gear" effect in apes and, as a consequence, probably a different auditory acuity. Although only a few fossil Neanderthal auditory ossicles are known, it may be, nevertheless, of interest studying the ossicles from the viewpoint of vibration transfer impedance function. The methodology may also be appropriate to study the few Australopithecine ossicles that are known. It is a matter of question whether the ossicles may have a meaning in distinguishing human populations; nevertheless, at least a case of clear distinction between human population has been achieved as in the case of Antinoe Roman-Egyptians.

No abstract