An allometric study of anthropoid cranial bone thickness: Implications for body size estimation in early hominid specie

This study examined the interspecific allometric relationship between measures of total cranial bone thickness and body size in a series of extant anthropoid primates, including Homo sapiens and in a sample of extinct hominid species, including Australopithecus africanus, Homo erectus and archaic Homo sapiens. The results of regression analyses based on the extant anthropoid sample demonstrated that most of the interspecific variation in bone thickness is explained by variation in body mass. Using estimates of body weight derived from the literature, the fossil hominid sample displayed a covariance and scaling relationship which was weak and dissimilar to that observed in extant anthropoids. When patterns in the distribution of residual variance throughout the cranium were compared, fossil hominids displayed a pattern which was consistent with that describing modern species. These data suggested that, when published body weight estimates are used to represent fossil hominids, there is disruption in the bone thickness/body size relationship which characterizes modern anthropoids, while continuity in the pattern of non-size related variance is maintained. It was concluded that the weak relationship between vault bone thickness and body mass exhibited in the fossil hominid sample is most reasonably explained by the use of inaccurate body weight estimates for some of these groups. After assessing several parameters, five measures of cranial bone thickness were judged as reliable predictors of body mass among modern primates. When these measures were used to generate body weight estimates in the fossil hominid sample, mean species predicted values for A. africanus were consistent with body weight estimates generated from post cranial morphological parameters. For members of the genus Homo, predicted body weights were significantly higher than previous estimates. Estimates of mean species body mass in the particularly well represented Asian H. erectus sample fell between 83 and 123 kg.