Jeffrey K. McKee

Forecasting global biodiversity threats associated with human population growth

Abstract The size and growth of the human population are often cited as key factors in threats to Earth’s biodiversity, yet the extent of their contribution to the endangerment and extinction of other species has remained unclear. Moreover, it could be valuable to know what additional threats may arise from continued human population growth. Here we quantify a model of the relationship between human population density and the number of threatened mammal and bird species by nation. Our multiple regression analysis revealed that two predictor variables, human population density and species richness (of birds and mammals), account for 88% of the variability in log-transformed densities of threatened species across 114 continental nations. Using the regression model with projected population sizes of each nation, we found that the number of threatened species in the average nation is expected to increase 7% by 2020, and 14% by 2050, as forecast by human population growth alone. Our findings strongly support the notion that abating human population growth is a necessary, if not sufficient, step in the epic attempt to conserve biodiversity on the global scale.

Tooth Wear Rates Among Contemporary Australian Aborigines

Most reports of Aboriginal tooth wear have been descriptive, and few have dealt with the question of wear rate. This study records cusp heights of dental casts taken from individuals during a growth study of Aboriginal children from ages six to 18. Their rates of wear were greater than those of Europeans, and the most rapid rate was recorded among Aboriginal males. These differences are due to the quantity of dietary abrasives.

Faunal turnover rates and mammalian biodiversity of the late Pliocene and Pleistocene of eastern Africa

Abstract Two models of faunal turnover patterns, one with constant turnover and another with climatically induced turnover pulses, were tested against the empirical fossil data of first and last appearances of large mammals from the late Pliocene and Pleistocene of East Africa. Computer simulations of each model were generated by first creating change in hypothetical faunal communities and then sampling the evolving communities in a manner scaled to the specific contingencies of the East African fossil record. Predictions of the two turnover models were compared with the empirical data. Neither model yielded predictions that deviated significantly from the observed patterns of first and last appearances of species, and both models produced extremely similar results. The implication is that the fossil data of East Africa are not refined enough to detect variations in the pace of turnover; the patterns of first- and last-appearance frequencies are determined more by the contingencies of the fossil record than by the underlying evolutionary and migrational patterns. Whereas these results undermine the primary basis of empirical support for the turnover-pulse hypothesis, they do not imply that other models are more likely. However, the simulation results were highly suggestive of significant reduction in species biodiversity of large mammals during the past 2 Myr.

FORMATION AND GEOMORPHOLOGY OF CAVES IN CALCAREOUS TUFAS AND IMPLICATIONS FOR THE STUDY OF THE TAUNG FOSSIL DEPOSITS

SUMMARY Models of cave site formation processes in calcareous tufa accretions are necessary for the interpretation of fossiliferous cave deposits exposed by quarrying and excavation. The ancient system of caves in the Thabaseek tufa at the Buxton Limeworks near Taung yielded the Taung hominid skull, type specimen of Australopithecus africanus, in 1924. Since then no consensus has been reached concerning the precise location of the Type Site, the geological age of the Taung hominid or the nature of the caves in which it became interred. Recent excavations of fossil deposits in the Thabaseek tufa, near the putative Type Site, in association with the historical records, have revealed new clues as to the provenance of the Taung hominid and the nature of the cave from which it was excavated. An investigation of caves in tufa accretions of the Ghaap escarpment and Eastern Transvaal has revealed four types of tufa caves that can be used as models for analysis of the fossil deposits. These include carapace caves,...

Craniodental remains of Papio angusticeps from the haasgat cave site, South Africa

Haasgat is a fossil-bearing cave site that has yielded 83 craniodental fossils of early Papio.All of the Haasgat cave baboon fossil collection may be identified as Papio angusticeps.The Haasgat fossils of P. angusticepsextend the previously known size range of the species as identified at other sites. The concordance of this and other fauna with that of Kromdraai suggest that Haasgat probably dates to the terminal Pliocene. We hypothesize that the Haasgat baboons and associated fauna were accumulated by versatile predators operating in a cave in a montane forest environment with savannah or open woodland nearby.

Measurement error in human dental mensuration

The reliability of human odontometric data was evaluated in a sample of 60 teeth. Three observers, using their own instruments and the same definition of the mesiodistal and buccolingual dimensions were asked to repeat their measurements after 2 months. Precision, or repeatability, was analysed by means of Pearsonian correlation coefficients and mean absolute error values. Accuracy, or the absence of bias, was evaluated by means of Bland-Altman procedures and attendant Student t-tests, and also by an ANOVA procedure. The present investigation suggests that odontometric data have a high interobserver error component. Mesiodistal dimensions show greater imprecision and bias than buccolingual measurements. The results of the ANOVA suggest that bias is the result of interobserver error and is not due to the time between repeated measurements.

New species of Cercopithecoides from Haasgat, North West Province, South Africa

Analyses of new cercopithecid fossil specimens from the South African site of Haasgat point to craniofacial affinities with the genus Cercopithecoides. Detailed metric and non-metric comparisons with South African Cercopithecoides williamsi, and other East African Cercopithecoides species, Cercopithecoides kimeui, Cercopithecoides meaveae, Cercopithecoides kerioensis, and Cercopithecoides alemyehui demonstrate that the Haasgat fossils have distinct craniofacial morphology and dental metrics. Specifically, material from Haasgat probably represents one of the smaller Cercopithecoides, differing from the others in its particular suite of features that vary within the genus. It is unique in its more vertical ramus, associated with a relatively lengthened mandibular body. Haasgat Cercopithecoides has a particularly narrow interorbital region between relatively larger ovoid orbits, with articulation of the maxillary bones at a suture above the triangular nasal bones. Furthermore, the maxillary arcade is more rounded than other Cercopithecoides, converging at the M(2) and M(3). The conclusion drawn from this analysis is that the Pleistocene Haasgat fossils are colobines representing a distinct taxon of Cercopithecoides, Cercopithecoides haasgati, thus adding a second species of the genus to southern Africa.

Correlates of enamel hypoplasia with human dental reduction

Human dental reduction has been manifested in evolutionary and secular trends, but it is not known to what degree each of these complementary processes contributes to changes in tooth size. Enamel hypoplasia is a marker of developmental stress that is often found to be of greater frequency and severity in populations undergoing dental size reduction. In order to test the developmental association of enamel hypoplasia with tooth size, measurements of bucco‐lingual and mesio‐distal diameters were taken on teeth of 54 black male skulls from southern Africa. Those dentitions that exhibited incisal enamel hypoplasia were significantly reduced in size as compared to those showing no signs of developmental stress. A distinct pattern of reduction emerged: the bucco‐lingual diameters of the I1, I2, P3, P4, M1, and M2 were significantly reduced, whereas the mesio‐distal diameters of only the I2 and M2 decreased in size. The I2 and M2 showed the greatest degree of reduction despite the lack of macroscopic enamel hypoplasia on the M2. Application of the data to the variety of dental reduction patterns evinced in modern and ancient populations indicates that factors including tooth shape, developmental timing of stress, and genetic determinants of tooth size must be considered in order to partition evolutionary and secular trends in the dentition.

The Dart Deposits of the Buxton Limeworks, Taung, South Africa, and the context of the Taung Australopithecus fossil

ABSTRACT The geologic, environmental, and taphonomic context of the Taung Australopithecus africanus skull has been the subject of speculation and sporadic research since its first publication. In order to refine our contextual knowledge of this important hominin fossil, systematic excavations of the Taung fossil site at the Buxton Limeworks, in the Taung district of what is now the North West Province of South Africa, were conducted from 1988 to 1993. The excavations began on the Hrdlička pinnacle, where Aleš Hrdlička had found fossiliferous deposits in 1925. A separate set of deposits, closer to the reconstructed position of the 1924 Australopithecus discovery and more consistent with the historical record of the Taung discovery, was uncovered on the quarry floor, 42 m southwest of and 6 m lower than the nearest Hrdlička deposits. The fossils of these three distinct deposits, known as the ‘Dart deposits,’ are sparsely distributed, representing different taphonomic conditions and most likely older than most previous discoveries. There are 16 cercopithecid fossils and four bovid fossils, along with eggshell, turtle shell, brachiopods, and reed casts. They provide the most immediate context for the depositional conditions of the Taung Australopithecus juvenile.

Variability of the hominid juxtamastoid eminence and associated basicranial features

Abstract The juxtamastoid eminence is a ridge of bone associated with the attachment of the posterior belly of the digastric muscle. It is found in some hominids, but not in other primates, and is therefore considered to be a derived feature. We dissected 30 human cadavers and studied 229 modern human skulls to assess the range of variation and functional morphology of the juxtamastoid eminence. It was found that the mastoid region was highly variable both in form of the juxtamastoid eminence as well as in its relations to muscle attachments and adjacent bony features. In light of our observations, the mastoid regions of original hominid fossils from southern Africa were scrutinized. It was concluded that the fossils showed variability in the presence of the juxtamastoid eminence, and that the ambiguity of the mastoid regions preservation and interpretation was too great to use the eminence as a reliable taxonomic or phylogenetic indicator.