A reconstruction of the Vienna skull of Hadropithecus stenognathus.

Franz Sikora found the first specimen and type of the recently extinct Hadropithecus stenognathus in Madagascar in 1899 and sent it to Ludwig Lorenz von Liburnau of the Austrian Imperial Academy of Sciences. Later, he sent several more specimens including a subadult skull that was described by Lorenz von Liburnau in 1902. In 2003, some of us excavated at the locality and found more specimens belonging to this species, including much of a subadult skeleton. Two frontal fragments were found, and these, together with most of the postcranial bones, belong to the skull. CT scans of the skull and other jaw fragments were made in Vienna and those of the frontal fragments at Penn State University. The two fragments have been reunited with the skull in silico, and broken parts from one side of the skull have been replaced virtually by mirror-imaged complete parts from the other side. The parts of the jaw of another individual of a slightly younger dental age have also been reconstructed virtually from CT scans with mirror imaging and by using the maxillary teeth and temporomandibular joints as a guide to finish the reconstruction. Apart from forming a virtual skull for biomechanical and systematic analysis, we were also able to make a virtual endocast. Missing anterior pieces were reconstructed by using part of an endocast of the related Archaeolemur majori. The volume is 115 ml. Hadropithecus and Archaeolemur seem to have had relatively large brains compared with the other large-bodied subfossil lemurs.

Conclusions: implications of the Liang Bua excavations for hominin evolution and biogeography.

Excavations at Liang Bua, on the Indonesian island of Flores, have yielded a stratified sequence of stone artifacts and faunal remains spanning the last 95k.yr., which includes the skeletal remains of two human species, Homo sapiens in the Holocene and Homo floresiensis in the Pleistocene. This paper summarizes and focuses on some of the evidence for Homo floresiensis in context, as presented in this Special Issue edition of the Journal of Human Evolution and elsewhere. Attempts to dismiss the Pleistocene hominins (and the type specimen LB1 in particular) as pathological pygmy humans are not compatible with detailed analyses of the skull, teeth, brain endocast, and postcranium. We initially concluded that H. floresiensis may have evolved by insular dwarfing of a larger-bodied hominin species over 880k.yr. or more. However, recovery of additional specimens and the numerous primitive morphological traits seen throughout the skeleton suggest instead that it is more likely to be a late representative of a small-bodied lineage that exited Africa before the emergence of Homo erectus sensu lato. Homo floresiensis is clearly not an australopithecine, but does retain many aspects of anatomy (and perhaps behavior) that are probably plesiomorphic for the genus Homo. We also discuss some of the other implications of this tiny, endemic species for early hominin dispersal and evolution (e.g., for the "Out of Africa 1" paradigm and more specifically for colonizing Southeast Asia), and we present options for future research in the region.

Dental microwear texture analysis of two families of subfossil lemurs from Madagascar.

This study employs dental microwear texture analysis to reconstruct the diets of two families of subfossil lemurs from Madagascar, the archaeolemurids and megaladapids. This technique is based on three-dimensional surface measurements utilizing a white-light confocal profiler and scale-sensitive fractal analysis. Data were recorded for six texture variables previously used successfully to distinguish between living primates with known dietary differences. Statistical analyses revealed that the archaeolemurids and megaladapids have overlapping microwear texture signatures, suggesting that the two families occasionally depended on resources with similar mechanical properties. Even so, moderate variation in most attributes is evident, and results suggest potential differences in the foods consumed by the two families. The microwear pattern for the megaladapids indicates a preference for tougher foods, such as many leaves, while that of the archaeolemurids is consistent with the consumption of harder foods. The results also indicate some intraspecific differences among taxa within each family. This evidence suggests that the archaeolemurids and megaladapids, like many living primates, likely consumed a variety of food types.

An evaluation of dental radiograph accuracy in the measurement of enamel thickness.

Many studies have employed lateral radiographs to measure the thickness of tooth enamel in recent human and fossil hominid samples, but the accuracy of measurements obtained by this technique has not been assessed. In this study, 20 isolated human maxillary permanent molars were radiographed using the parallel film technique. The crowns were then sectioned longitudinally through the tips of the buccal cusps. Measurements of enamel cap area, and of linear enamel thickness in the occlusal basin and over the metacone apex, were made from the radiographs and corresponding sectioned surfaces. Comparisons of the two sets of values revealed that radiographs generally overestimated enamel thickness but there was considerable variability in the error by which measurements from radiographs either under- or overestimated the true value. Lateral radiographs may provide a rough visual impression of whether a tooth has thin or thick enamel but they do not generally provide for accurate measurement of enamel thickness. Quantitative data on enamel thickness from studies that have employed lateral radiographs should be viewed with circumspection.

New discoveries of skeletal elements of Hadropithecus stenognathus from Andrahomana Cave, southeastern Madagascar.

Remains of what appears to be a single, subadult Hadropithecus stenognathus were recovered from a previously unexcavated site at Andrahomana Cave (southeastern Madagascar). Specimens found comprise isolated teeth and cranial fragments (including the frontal processes of the orbits), as well as a partial postcranial skeleton. They include the first associated fore- and hind-limb bones, confirming the hind-limb attributions made by Godfrey and co-workers in 1997, and refuting earlier attributions by Lamberton in 1937/1938. Of particular interest here are the previously unknown elements, including a sacrum, other vertebrae and ribs, some hand bones, and the distal epiphysis of a femur. We briefly discuss the functional implications of previously unknown elements. Hadropithecus displayed a combination of characters reminiscent of lemurids, others more like those of the larger-bodied Old World monkeys, and still others more like those of African apes. Yet other characteristics appear unique. Lemurid-like postcranial characteristics may be primitive for the Archaeolemuridae. Hadropithecus diverges from the Lemuridae in the direction of Archaeolemur, but more extremely so. Thus, for example, it exhibits a stronger reduction in the size of the hamulus of the hamate, greater anteroposterior compression of the femoral shaft, and greater asymmetry of the femoral condyles. Nothing in its postcranial anatomy signals a close relationship to either the Indriidae or the Palaeopropithecidae.

Elliptical fourier analysis of symphyseal shape in great ape mandibles.

The midsagittal profile of the mandibular symphysis has served as both a taxonomic marker and a phylogenetically salient character in debates over hominoid evolution. Nevertheless, the utility of symphyseal shape as an informative attribute for paleobiological reconstructions is suspect. Quantification of shape variation has proven to be particularly problematic; it has long been recognized that conventional linear measurements (and the indices derived from them), while replicable, summarize aspects of shape very poorly because of the vast amount of contour information that is lost in the process. In this study, a type of Fourier analysis is applied to cross-sectional contours of ape mandibles in order to provide a mathematical accounting of shape variation in a "global" sense; that is, by applying the "totality" of contour information in a comparative analysis. Shape variation in the mandibular symphysis is explored through the decomposition of coordinate data into elliptical Fourier coefficients. These coefficients are used to compute average taxonomic distances (ATD) among individuals of chimpanzees, gorillas, and orang-utans. The resulting shape-based distances are summarized via clustering (UPGMA) and ordination (principal coordinates analysis-PCO). Principal coordinate scores are subjected to analysis of variance in univariate and multivariate designs; these data are also applied to discriminant function analyses. Species and sex effects on morphology are statistically significant; however, no significant interaction of these factors is indicated. This would seem to imply that patterns of sexual dimorphism are not distinct among great apes; to the contrary, within-species sex comparisons reveal that significant size and shape dimorphism is present only in Gorilla. Despite significant size dimorphism in Pan and Pongo, significant shape differences between males and females are not apparent in these taxa. These results suggest that it is theoretically possible to sort taxa by a symphyseal shape criterion, but the discriminant function results suggest that there still exists a large potential for error in assigning particular shapes to a given species or sex. Thus, despite real shape differences among these species, the use of symphyseal shape as a character in species identification or in systematic arguments remains limited and problematic.

A re-evaluation of subspecific variation and canine dimorphism in woolly spider monkeys (Brachyteles arachnoides).

A recent study suggests that differing populations of woolly spider monkeys exhibit a substantial degree of morphological, cytogenetic, and behavioral variation. We re-evaluate the differences between populations in the degree of canine tooth height sexual dimorphism and in the frequency of thumbs. Statistical analysis of variation in the degree of canine sexual dimorphism between these populations fails to provide strong evidence for subspecific variation: differences in the degree of canine dimorphism cannot be considered statistically significant. Differences between populations in the frequency of thumbs are, however, statistically significant. The lack of clear distinctions between populations in the degree of canine dimorphism complicates assessments of behavioral variation between these populations. We suggest that the level of geographic variation in woolly spider monkey canine dimorphism is not consistent with subspecific status.

Supernumerary molars in Anthropoidea, Adapidae, and Archaeolemur: implications for primate dental homologies.

The model of primate dental homologies and development recently proposed by Schwartz ('75, '78) is re-evaluated in view of documented exceptions to his account of postcanine supernumerary teeth in both anthropoids and prosimians. Schwartz concluded that catarrhines and living indriids retain only two true molars in each dental quadrant. As many as six molars on one side of the jaw can develop in rare instances in catarrhines, and supernumerary molars are also known for a wide range of other primates, including Cebidae, Adapidae, and subfossil Indriidae. Polydontia cannot be explained exclusively by atavistic development. More convincing explanations regard supernumerary teeth as the result of excessive growth of the dental lamina or localized twinning of tooth buds during early development. Conventional dental formulae of catarrhines and indriids including three permanent molars remain the most plausible.

Molar microwear of subfossil lemurs: improving the resolution of dietary inferences.

In this study we use molar microwear analyses to examine the trophic distinctions among various taxa of Malagasy subfossil lemurs. High resolution casts of the teeth of Megaladapis, Archaeolemur, Palaeopropithecus, Babakotia, and Hadropithecus were examined under a scanning electron microscope. Megaladapis was undoubtedly a browsing folivore, but there are significant differences between species of this genus. However, dietary specialists appear to be the exception; for example, Palaeopropithecus and Babakotia probably supplemented their leaf-eating with substantial amounts of seed-predation, much like modern indrids. Hadropithecus was decidedly not like the modern gelada baboon, but probably did feed on hard objects. Evidence from microwear and coprolites suggests that Archaeolemur probably had an eclectic diet that differed regionally and perhaps seasonally. Substantial trophic diversity within Madgascar's primate community was diminished by the late Quaternary extinctions of the large-bodied species (>9 kg).

Analysis of individual, intraspecific and interspecific variability in quantitative parameters of caprine tooth enamel structure.

Qualitative and quantitative features of mammalian tooth enamel structure are increasingly being used in taxonomic and phylogenetic analyses, although the variability shown by these traits has not received adequate consideration. This study evaluates the variability displayed by nine quantitative parameters in deep, intermediate, and superficial molar enamel in the closely related bovids Ovis aries and Capra hircus. These parameters are assessed in terms of the absolute and/or relative variability evinced at a given depth within a single individual, among conspecific individuals, and between species samples. The degrees of relative variability expressed at a given depth are comparable among conspecific individuals and between taxonomic samples. Nevertheless, in many instances, there are significant differences in absolute variability amongst individuals. Also, in four parameters for which individual specimen averages could be calculated, the equality of these means among conspecifics can be rejected. Variability is not equivalent at different enamel depths. The null hypothesis of equality of individual, conspecific variances can be rejected most commonly for parameters measured in deep and superficial enamel, and coefficients of variation also tend to be higher for deep and superficial enamel than for enamel of intermediate depth. The greater variability displayed by deep and especially superficial enamel may be related to the initial onset and the terminal phase of ameloblastic secretory activity. Taxonomic and phylogenetic analyses that utilize quantitative data on enamel structure are valid only if comparisons have been made at equivalent enamel depths.

Phylogenetic and functional affinities of Babakotia (primates), a fossil lemur from northern Madagascar.

Recent paleontological expeditions to the Ankarana range of northern Madagascar have recovered the partial remains of four individuals of a newly recognized extinct lemur, Babakotia radofilai. Craniodental and postcranial material serve to identify Babakotia as a member of the palaeopropithecids (also including the extinct genera Palaeopropithecus, Archaeoindris, and Mesopropithecus). Living indrids form the sister group to this fossil clade. The postcranial anatomy indicates that Babakotia was a medium-sized (approximately 15 kg) indroid whose inferred positional behaviors were primarily slow climbing and hanging. Although it is probable that a leaping component typified the ancestral positional repertoire of all Malagasy lemurs, the mosaic nature of the locomotor skeleton of Babakotia further suggests that vertical climbing and hang-feeding rather than ricochetal leaping were primitive for indrids and palaeopropithecids and that the dramatic saltatory adaptations of the living indrids postdate the divergence of these two lineages.

Teeth, brains, and primate life histories.

This paper explores the correlates of variation in dental development across the order Primates. We are particularly interested in how 1) dental precocity (percentage of total postcanine primary and secondary teeth that have erupted at selected absolute ages and life cycle stages) and 2) dental endowment at weaning (percentage of adult postcanine occlusal area that is present at weaning) are related to variation in body or brain size and diet in primates. We ask whether folivores have more accelerated dental schedules than do like-sized frugivores, and if so, to what extent this is part and parcel of a general pattern of acceleration of life histories in more folivorous taxa. What is the adaptive significance of variation in dental eruption schedules across the order Primates? We show that folivorous primate species tend to exhibit more rapid dental development (on an absolute scale) than comparably sized frugivores, and their dental development tends to be more advanced at weaning. Our data affirm an important role for brain (rather than body) size as a predictor of both absolute and relative dental development. Tests of alternative dietary hypotheses offer the strongest support for the foraging independence and food processing hypotheses.

Ontogenetic correlates of diet in Malagasy lemurs.

There is a well-documented relationship between development and other life-history parameters among anthropoid primates. Smaller-bodied anthropoids tend to mature more rapidly than do larger-bodied species. Among anthropoids of similar body sizes, folivorous species tend to grow and mature more quickly than do frugivorous species, thus attaining adult body size at an earlier age. This pattern conforms to the expectations of Janson and van Schaik's "ecological risk aversion hypothesis," which predicts that rates of growth and maturation should vary in inverse relation to the intensity of intraspecific feeding competition. According to the ecological risk aversion hypothesis (RAH), species experiencing high intraspecific feeding competition will grow and mature slowly to reduce the risk of mortality due to food shortages. Species experiencing low levels of intraspecific feeding competition will shorten the juvenile period to reduce the overall duration of this high-risk portion of the life cycle. This paper focuses on development and maturation in lemurs. We show that folivorous lemurs (such as indriids) grow and mature more slowly than like-sized frugivorous lemurs (e.g., most lemurids), but tend to exhibit faster dental development. Their dental developmental schedules are accelerated on an absolute scale, relative to craniofacial growth, and relative to particular life-history landmarks, such as weaning. Dental development has a strong phylogenetic component: even those lemurids that consume substantial amounts of foliage have slower dental development than those indriids that consume substantial amounts of fruit. Implications of these results for the RAH are discussed, and an explanation for this hypothesis' failure to predict lemur growth schedules is offered. We propose that the differing developmental schedules of folivorous and frugivorous lemurs may reflect different solutions to the ecological problem of environmental instability: some rely on a strategy of low maternal input and slow returns, while others rely on a strategy of high maternal input and fast returns.