Richard S. Meindl

Sexual Dimorphism in Australopithecus afarensis Was Similar to That of Modern Humans

The substantial fossil record for Australopithecus afarensis includes both an adult partial skeleton [Afar Locality (A.L.) 288-1, “Lucy”] and a large simultaneous death assemblage (A.L. 333). Here we optimize data derived from both to more accurately estimate skeletal size dimorphism. Postcranial ratios derived from A.L. 288-1 enable a significant increase in sample size compared with previous studies. Extensive simulations using modern humans, chimpanzees, and gorillas confirm that this technique is accurate and that skeletal size dimorphism in A. afarensis was most similar to that of contemporary Homo sapiens. These data eliminate some apparent discrepancies between the canine and skeletal size dimorphism in hominoids, imply that the species was not characterized by substantial sexual bimaturation, and greatly increase the probability that the reproductive strategy of A. afarensis was principally monogamy.

Fetal age: Methods of estimation and effects of pathology

Accurate identification of fetal age is important in a wide variety of circumstances. Seventeen anthropometric and radiographic measurements were taken on fetuses between 15 and 42 weeks of gestational age, both with and without pathologic conditions. A full evaluation including radiographic, karyotypic, gross anatomic, and histologic examination of the fetus and placenta identified 72 individuals as nondysmorphic with no signs of chronic uterovascular insufficiency. These specimens served as the control group. Based on least-squares regressions of this group, age-estimation equations were calculated for all variables. Six models were adequately described by linear equations; the remaining 11 required a quadratic term. Based on standard error of the estimate (S(y:x)), skeletal measures proved the most accurate age estimators. Pathologic conditions were shown to have an influence on age estimation indicated by high levels of inaccuracy and, in some instances, significant bias.

Hominoid dental maturation

Abstract Traditional analyses of dental eruption pattern and enamel attrition suggested that the South African australopithecines exhibited a human-like or delayed maturation rate. Recent work has challenged this view by proposing that early hominids matured at a rate more like extant apes. We show that relative growth rates of ape and human dental structures are essentially similar, and that pattern differences in calcification stem from hominid incisor and canine reduction with concomitant facial reorganization. Pattern of dental development alone cannot be used to infer rates of somatic maturation.

An enlarged postcranial sample confirms Australopithecus afarensis dimorphism was similar to modern humans

In a previous study, we introduced the template method as a means of enlarging the Australopithecus afarensis postcranial sample to more accurately estimate its skeletal dimorphism. Results indicated dimorphism to be largely comparable to that of Homo sapiens. Some have since argued that our results were biased by artificial homogeneity in our Au. afarensis sample. Here we report the results from inclusion of 12 additional, newly reported, specimens. The results are consistent with those of our original study and with the hypothesis that early hominid demographic success derived from a reproductive strategy involving male provisioning of pair-bonded females.

Students With Intellectual Disabilities Predictors of Transition Outcomes

This study examined the outcomes of 409 students with mental retardation or multiple disabilities from 177 school districts in a Great Lakes state. These students with intellectual disabilities were interviewed at exit and 1 year following graduation. The authors developed and tested three regression models—two to predict full-time employment and one to predict college enrollment after graduation. Although inclusion was a significant predictor of postsecondary education, career and technical education and work study programs did not reach significance as predictors of postschool employment. For these students, gender and minority issues contributed to most of the variance. These findings point to the need for more holistic career and technical education and work study models for these students.

Variation in Mammalian Proximal Femoral Development: Comparative Analysis of Two Distinct Ossification Patterns

The developmental anatomy of the proximal femur is complex. In some mammals, including humans, the femoral head and greater trochanter emerge as separate ossification centres within a common chondroepiphysis and remain separate throughout ontogeny. In other species, these secondary centres coalesce within the chondroepiphysis to form a single osseous epiphysis much like the proximal humerus. These differences in femoral ontogeny have not been previously addressed, yet are critical to an understanding of femoral mineralization and architecture across a wide range of mammals and may have key implications for understanding and treating hip abnormalities in humans. We evaluated femora from 70 mammalian species and categorized each according to the presence of a ‘separate’ or ‘coalesced’ proximal epiphysis based on visual assessment. We found that ossification type varies widely among mammals: taxa in the ‘coalesced’ group include marsupials, artiodactyls, perissodactyls, bats, carnivores and several primates, while the ‘separate’ group includes hominoids, many rodents, tree shrews and several marine species. There was no clear relationship to body size, phylogeny or locomotion, but qualitative and quantitative differences between the groups suggest that ossification type may be primarily an artefact of femoral shape and neck length. As some osseous abnormalities of the human hip appear to mimic the normal morphology of species with coalesced epiphyses, these results may provide insight into the aetiology and treatment of human hip disorders such as femoroacetabular impingement and early‐onset osteoarthritis.

An Epidemiological Model of Transition and Postschool Outcomes

This longitudinal transition study was conducted in collaboration with teachers who interviewed students who graduated from 177 school districts in a Great Lakes state. Special education students were interviewed at exit and 1 year following graduation using a survey based on the National Longitudinal Transition Study. The data were analyzed using logistic regression models that controlled for gender, minority status, and level of disability. The authors developed and tested three regression models: two to predict full-time employment and one to predict college enrollment. Students who graduated from career and technical education and work study programs were more likely to enter full-time employment after graduation, but this relationship was influenced by gender, minority status, and disability. Students who participated in mainstream academics were much more likely to be enrolled in full-time college after graduation, but this relationship was influenced by level of disability.

Histomorphological and geometric properties of human femoral cortex in individuals over 50: Implications for histomorphological determination of age‐at‐death

Cortical area, area moment of inertia, and polar moment of inertia were determined from the midshafts of a series of 62 femurs (34 female and 28 male) from a U. S. white population, ages 51–95. The density of osteons and osteon fragments (per mm2) was also determined. Neither osteon nor osteon fragment density was significantly correlated with age. These variables were correlated, however, with normalized cortical and endosteal areas, normalized area moment of inertia, and polar moment of inertia. Osteon fragment numbers alone are not highly correlated with cross‐sectional properties. This research suggests that osteon density and osteon fragment density are significantly related to cortical mass and distribution in older people, but are not a direct function of age in persons over 50 years of age. Histological age estimates in older individuals must, therefore, be used with extreme caution.

Adaptationism and the anthropoid postcranium: Selection does not govern the length of the radial neck

The length of the radial neck has been assumed to vary in living and extinct primates in accordance with its role as a moment arm during flexion by the m. biceps brachii. We here use a simple developmental approach to investigate whether or not this trait does, in fact, vary in such a manner. We find, instead, that virtually all variation in radial neck length is explicable as a simple correlate of overall body size, and that there is no evidence to conclude that selection has separately modified radial neck length in response to differing locomotor patterns. Further implications for the interpretation of mammalian skeletal morphology are briefly discussed. J. Morphol. 246:59–67, 2000

Ectocranial Suture Closure in Pan troglodytes and Gorilla gorilla: Pattern and Phylogeny

The order in which ectocranial sutures undergo fusion displays species-specific variation among primates. However, the precise relationship between suture closure and phylogenetic affinities is poorly understood. In this study, we used Guttman Scaling to determine if the modal progression of suture closure differs among Homo sapiens, Pan troglodytes, and Gorilla gorilla. Because DNA sequence homologies strongly suggest that P. troglodytes and Homo sapiens share a more recent common ancestor than either does with G. gorilla, we hypothesized that this phylogenetic relationship would be reflected in the suture closure patterns of these three taxa. Results indicated that while all three species do share a similar lateral-anterior closure pattern, G. gorilla exhibits a unique vault pattern, which, unlike humans and P. troglodytes, follows a strong posterior-to-anterior gradient. P. troglodytes is therefore more like Homo sapiens in suture synostosis.