No abstract

Tooth emergence data from a mixed-longitudinal sample of 58 chimpanzees of known age were analyzed using probit and survival techniques to produce median emergence ages, ranges of variability, and emergence sequences for primary and permanent teeth. Between-group comparisons were made to test for statistically significant differences in emergence ages. No such differences were found between right and left sides, or between maxilla and mandible, for any primary or permanent teeth. Male-female comparisons did demonstrate significant emergence-age differences for some teeth, although they were not always bilaterally symmetrical. More complete data are required to further clarify the nature of sex differences in tooth emergence in chimpanzees. Regression models for age prediction from the number of emerged teeth were generated and indicate that males achieve a given number of emerged teeth at a significantly later age than females. However, when fewer than five teeth have emerged, males are predicted to be younger than females. The sizable root mean square error values for these models suggest that this method of age prediction has limited usefulness owing to the amount of variability in timing of tooth emergence in chimpanzees. The implications of these data for studies on tooth emergence in early hominids are addressed.

A noninvasive computer imaging technique allows three-dimensional images of fossil skulls to be generated from two-dimensional serial computerized tomographic scan data. The computer programs can "dissect" the skull in different planes by making portions of it and any obstructing matrix transparent in order to reveal intracranial morphology. The computer image is geometrically precise so that linear distances, angles, areas, volumes, and evaluations of symmetry can be determined.

KEY WORDS ingGrowth and development, Teeth, Maturation, Ag- ABSTRACTDental emergence ages are examined for a mixed longitudinal sample of 58 chimpanzees of known age and sex (22 males, 36 females) followed over the past 10 years. This study provides the most complete data set currently available on dental emergence in chimpanzees of known age and sex. Summary statistics and cumulative frequency percentiles of emergence ages are presented for both the permanent and the primary teeth. Male and female percentiles are also compared and reveal a number of cases of sexual dimorphism in emergence ages. Comparisons of emergence means reveal some statistically significant differences between upper and lower teeth but not between antimeres in the upper or lower dentition. Kendall's rank correlation coefficient (tau) suggests a correlation in timing between first molar and incisor emergence within individuals. In addition, a significant time lag was observed between first molar and central incisor emergence. A number of emergence sequence polymorphisms are presented as well. These findings provide important baseline information for future studies of chimpanzee growth, development, and demography and also contribute to several current issues in paleoanthropology relating to dental maturation patterns in early hominids.

Just over 60 years ago, Dart's description and analysis of the Taung child's skull triggered an intellectual revolution about human origins. Recently, several authors have suggested that one of the most significant hominid-like traits of australopithecines, delayed maturation, may not after all be valid. This is a radical departure from Mann's classic study of australopithecine maturation and palaeodemography based on dental eruption patterns. The resolution of this debate has important implications for the history of the biological and social evolution of the human species. In view of the controversies generated by recent studies, and particularly because the Taung skull is the type specimen of Australopithecus africanus, we have investigated the relevant anatomy of the Taung 'child' using computerized tomography. We conclude that the Taung 'child' shows some important dental maturational affinities with great apes, although as Dart noted, other hominid-like features are clearly present.