F.C. de Beer

Disproportionate Cochlear Length in Genus Homo Shows a High Phylogenetic Signal during Apes' Hearing Evolution.

Changes in lifestyles and body weight affected mammal life-history evolution but little is known about how they shaped species’ sensory systems. Since auditory sensitivity impacts communication tasks and environmental acoustic awareness, it may have represented a deciding factor during mammal evolution, including apes. Here, we statistically measure the influence of phylogeny and allometry on the variation of five cochlear morphological features associated with hearing capacities across 22 living and 5 fossil catarrhine species. We find high phylogenetic signals for absolute and relative cochlear length only. Comparisons between fossil cochleae and reconstructed ape ancestral morphotypes show that Australopithecus absolute and relative cochlear lengths are explicable by phylogeny and concordant with the hypothetized ((Pan,Homo),Gorilla) and (Pan,Homo) most recent common ancestors. Conversely, deviations of the Paranthropus oval window area from these most recent common ancestors are not explicable by phylogeny and body weight alone, but suggest instead rapid evolutionary changes (directional selection) of its hearing organ. Premodern (Homo erectus) and modern human cochleae set apart from living non-human catarrhines and australopiths. They show cochlear relative lengths and oval window areas larger than expected for their body mass, two features corresponding to increased low-frequency sensitivity more recent than 2 million years ago. The uniqueness of the “hypertrophied” cochlea in the genus Homo (as opposed to the australopiths) and the significantly high phylogenetic signal of this organ among apes indicate its usefulness to identify homologies and monophyletic groups in the hominid fossil record.

NEUTRON RADIOGRAPHY APPLICATIONS IN STUDIES OF DRYING OF CAPILLARY-POROUS SYSTEMS

The application of modern digital neutron radiography in the study of the drying process in porous media is demonstrated with two simple examples of cylindrical and rectangular samples made of different materials. The statistical method of image analysis is presented and the standard deviation of grey scale values (referred to brightness) is shown to be a useful measure of receding drying front emergence. The motion of the drying front was analyzed and found neither linear nor proportional to the square root of time and was delineated with nonlinear functions different for each sample shape.

The late Middle Pleistocene upper third molar from Florisbad : metrics and morphology

In the early 1930s an upper right third molar (M3) together with a calotte and fragmented facial bones of an adult fossil hominin was recovered during excavations at Florisbad. The M3 is one of the few well-dated teeth associated with cranial remains from the late Mid-Pleistocene in southern Africa and as such provides a valuable addition to the fossil dental record of this region. Here we provide a detailed description of the tooth based on standard measurements and 3D images derived from high resolution micro-high resolution micro-focus X-ray tomography. Our results show that the Florisbad M3 falls within the size range of African Homo erectus. It is slightly larger than other peri-contemporary M3s known from Africa that date from the Middle to Late Pleistocene. Like them, however, it also falls within the size range of recent, large-toothed African populations. These results suggest the maintenance of selective pressures favouring large teeth in some African populations until the present.