Dental use wear in extinct lemurs: evidence of diet and niche differentiation

Arid, mosaic environments during the Plio-Pleistocene transition and early hominin dispersals in northern Africa

The earliest archaeological evidence from northern Africa dates to ca. 2.44 Ma. Nevertheless, the palaeoenvironmental setting of hominins living in this part of the continent at the Plio-Pleistocene transition remains poorly documented, particularly in comparison to eastern and southern Africa. The Guefaït-4 fossil site in eastern Morocco sheds light on our knowledge of palaeoenvironments in northern Africa. Our study reveals the oldest known presence of C4 plants in the northern part of the continent in a mosaic landscape that includes open grasslands, forested areas, wetlands, and seasonal aridity. This diverse landscape and resource availability likely facilitated the occupation of the region by mammals, including potentially hominins. Our regional-scale study provides a complementary perspective to global-scale studies and highlights the importance of considering the diversity of microhabitats within a given region when studying species-dispersal dynamics.

Dental caries in living and extinct strepsirrhines with insights into diet

Dental caries is one of the most common diseases afflicting modern humans and occurs in both living and extinct non-human primates, as well as other mammalian species. Compared to other primates, less is known about the etiology or frequency of caries among the Strepsirrhini. Given the link between caries and diet, caries frequency may be informative about the dietary ecology of a given animal. Understanding rates of caries in wild populations is also critical to assessing dental health in captive populations. Here, we examine caries frequency in a sample of 36 extant strepsirrhine species (n = 316 individuals) using odontological collections of wild-, non-captive animals housed at the American Museum of Natural History by counting the number of specimens characterized by the disease. Additionally, in the context of studying caries lesions in strepsirrhines, case studies were also conducted to test if similar lesions were found in their fossil relatives. In particular, two fossil strepsirrhine species were analyzed: the earliest Late Eocene Karanisia clarki, and the subfossil lemur Megaladapis madagascariensis. Our results suggest that caries affects 13.92% of the extant individuals we examined. The frugivorous and folivorous taxa were characterized by the highest overall frequency of caries, whereas the insectivores, gummivores, and omnivores had much lower caries frequencies. Our results suggest that caries may be common among wild populations of strepsirrhines, and in fact is more prevalent than in many catarrhines and platyrrhines. These findings have important implications for understanding caries, diet, and health in living and fossil taxa.

Uncovering widespread Anthropocene dietary shifts in Chinese large mammalian herbivores

The Anthropocene's human-dominated habitat expansion endangers global biodiversity. However, large mammalian herbivores experienced few extinctions during the 20th century, hinting at potentially overlooked ecological responses of a group sensitive to global change. Using dental microwear as a proxy, we studied large herbivore dietary niches over a century across mainland China before (1880s-1910s) and after (1970s-1990s) the human population explosion. We uncovered widespread and significant shifts (interspecific microwear differences increased and intraspecific microwear dispersion expanded) within dietary niches linked to geographical areas with rapid industrialization and population growth in eastern China. By contrast, in western China, where human population growth was slower, we found no indications of shifts in herbivore dietary niches. Further regression analysis links the intensity of microwear changes to human land-use expansion. These analyses highlight dietary adjustments of large herbivores as a likely key factor in their adaptation across a century of large-scale human-driven changes.

Multiproxy approach to reconstruct fossil primate feeding behavior: Case study for macaque from the Plio-Pleistocene site Guefaït-4.2 (eastern Morocco)

The genus Macaca belongs to Cercopithecidae (Old World monkeys), Cercopithecinae, Papionini. The presence of Macaca in North Africa is well known from the Late Miocene to the Late Pleistocene. However, the diet of fossil Macaca has been poorly described in the literature. In this study, we investigated the feeding habits of Macaca cf. sylvanus (n = 4) from the Plio-Pleistocene site Guefaït-4.2 in eastern Morocco through multiproxy analysis combining analyses of stable carbon and oxygen isotopes from tooth enamel, buccal microtexture, and low-magnification occlusal dental microwear. For both microwear analyses, we compared the macaques with a new reference collection of extant members of Cercopithecoidea. Our occlusal microwear results show for the fossil macaque a pattern similar to the extant Cercocebus atys and Lophocebus albigena, African forest-dwelling species that are characterized by a durophagous diet based mainly on hard fruit and seed intake. Buccal microtexture results also suggest the consumption of some grasses and the exploitation of more open habitats, similar to that observed in Theropithecus gelada. The δ13C of M. cf. sylvanus indicates a C3 based-diet without the presence of C4 plants typical of the savanna grassland in eastern Africa during this period. The high δ18O values of M. cf. sylvanus, compared with the contemporary ungulates recovered from Guefaït-4.2, could be associated with the consumption of a different resource by the primate such as leaves or fresh fruits from the upper part of trees. The complementarity of these methods allows for a dietary reconstruction covering a large part of the individual’s life.

Dental macrowear, diet, and anterior tooth use in Colobus polykomos and Piliocolobus badius

Two similarly-sized colobine species living sympatrically in the Ivory Coast's Taï Forest that differ in both diet and oral processing behavior provide an opportunity to explore the strength of associations between feeding behavior and dental wear patterns. Here we test the hypothesis that vigorous processing of tough, hard Pentaclethra macrophylla pods by Colobus polykomos manifests in greater anterior tooth wear relative to that observed in Piliocolobus badius, which does not exploit this resource. We assessed levels of anterior tooth wear in a sample of 160 upper incisors and 131 lower incisors from 18 adult Colobus polykomos and 62 adult Piliocolobus badius naturally deceased individuals from Taï National Park. We operationalized tooth wear by dividing the area of exposed dentin by total occlusal crown area. To assess relative degrees of incisor wear, we regressed incisor wear against molar wear (sample = 105 upper molars, 135 lower molars) for the pooled Colobus polykomos and Piliocolobus badius wear data and compared the number of individuals from each species that fell above and below the pooled regression curve for each model using Chi-square tests of independence and odds ratios. Under our hypothesis, we would expect more Colobus polykomos points above the pooled regression curve than Piliocolobus badius, indicating higher incisor wear relative to molar wear in Colobus polykomos. Nine of sixteen interspecific comparisons demonstrated this predicted pattern; however, none of the Chi-square tests or odds ratios were significant, indicating no difference between Colobus polykomos and Piliocolobusbadius incisor wear relative to molar wear. The absence of significant differences in incisor wear relative to molar wear highlights the challenge of identifying idiosyncratic feeding behavior in fossil taxa and the necessity for continued exploration of the relationship between diet and macrowear.

Evolutionary and phylogenetic insights from a nuclear genome sequence of the extinct, giant, "subfossil" koala lemur Megaladapis edwardsi

No endemic Madagascar animal with body mass >10 kg survived a relatively recent wave of extinction on the island. From morphological and isotopic analyses of skeletal "subfossil" remains we can reconstruct some of the biology and behavioral ecology of giant lemurs (primates; up to ∼160 kg) and other extraordinary Malagasy megafauna that survived into the past millennium. Yet, much about the evolutionary biology of these now-extinct species remains unknown, along with persistent phylogenetic uncertainty in some cases. Thankfully, despite the challenges of DNA preservation in tropical and subtropical environments, technical advances have enabled the recovery of ancient DNA from some Malagasy subfossil specimens. Here, we present a nuclear genome sequence (∼2× coverage) for one of the largest extinct lemurs, the koala lemur Megaladapis edwardsi (∼85 kg). To support the testing of key phylogenetic and evolutionary hypotheses, we also generated high-coverage nuclear genomes for two extant lemurs, Eulemur rufifrons and Lepilemur mustelinus, and we aligned these sequences with previously published genomes for three other extant lemurs and 47 nonlemur vertebrates. Our phylogenetic results confirm that Megaladapis is most closely related to the extant Lemuridae (typified in our analysis by E. rufifrons) to the exclusion of L. mustelinus, which contradicts morphology-based phylogenies. Our evolutionary analyses identified significant convergent evolution between M. edwardsi and an extant folivore (a colobine monkey) and an herbivore (horse) in genes encoding proteins that function in plant toxin biodegradation and nutrient absorption. These results suggest that koala lemurs were highly adapted to a leaf-based diet, which may also explain their convergent craniodental morphology with the small-bodied folivore Lepilemur.

Functional traits of the world's late Quaternary large-bodied avian and mammalian herbivores

Prehistoric and recent extinctions of large-bodied terrestrial herbivores had significant and lasting impacts on Earth's ecosystems due to the loss of their distinct trait combinations. The world's surviving large-bodied avian and mammalian herbivores remain among the most threatened taxa. As such, a greater understanding of the ecological impacts of large herbivore losses is increasingly important. However, comprehensive and ecologically-relevant trait datasets for extinct and extant herbivores are lacking. Here, we present HerbiTraits, a comprehensive functional trait dataset for all late Quaternary terrestrial avian and mammalian herbivores ≥10 kg (545 species). HerbiTraits includes key traits that influence how herbivores interact with ecosystems, namely body mass, diet, fermentation type, habitat use, and limb morphology. Trait data were compiled from 557 sources and comprise the best available knowledge on late Quaternary large-bodied herbivores. HerbiTraits provides a tool for the analysis of herbivore functional diversity both past and present and its effects on Earth's ecosystems.

Evolution of bone cortical compactness in slow arboreal mammals

Convergent evolution is a major topic in evolutionary biology. Low bone cortical compactness (CC, a measure of porosity of cortical bone) in the extant genera of "tree sloths," has been linked to their convergent slow arboreal ecology. This proposed relationship of low CC with a slow arboreal lifestyle suggests potential convergent evolution of this trait in other slow arboreal mammals. Femoral and humeral CC were analyzed in "tree sloths," lorisids, koala, and extinct palaeopropithecids and Megaladapis, in comparison to closely related but ecologically distinct taxa, in a phylogenetic framework. Low CC in "tree sloths" is unparalleled by any analyzed clade and the high CC in extinct sloths suggests the recent convergence of low CC in "tree sloths." A tendency for low CC was found in Palaeopropithecus and Megaladapis. However, lorisids and the koala yielded unexpected CC patterns, preventing the recognition of a straightforward convergence of low CC in slow arboreal mammals. This study uncovers a complex relationship between CC and convergent evolution of slow arboreality, highlighting the multifactorial specificity of bone microstructure.

Dental microwear texture analysis and diet in caviomorphs (Rodentia) from the Serra do Mar Atlantic forest (Brazil)

The Serra do Mar Atlantic forest (Brazil) shelters about 15 different species of caviomorph rodents and thus represents a unique opportunity to explore resource partitioning. We studied 12 species with distinct diets using dental microwear texture analysis (DMTA). Our results revealed differences (complexity, textural fill volume, and heterogeneity of complexity) among species with different dietary preferences, and among taxa sharing the same primary dietary components but not those with similar secondary dietary preferences (heterogeneity of complexity). We found three main dietary tendencies characterized by distinct physical properties: consumers of young leaves had low complexity; bamboo specialists, fruit and seed eaters, and omnivorous species, had intermediate values for complexity; grass, leaf, and aquatic vegetation consumers, had highly complex dental microwear texture. Dietary preferences and body mass explained a major part of the resource partitioning that presumably enables coexistence among these rodent species. DMTA was useful in assessing what foods contributed to resource partitioning in caviomorphs. Our database for extant caviomorph rodents is a prerequisite for interpretation of dental microwear texture of extinct caviomorph taxa, and thus for reconstructing their diets and better understanding the resource partitioning in paleocommunities and its role in the successful evolutionary history of this rodent group.

Complementary approaches to tooth wear analysis in Tritylodontidae (Synapsida, Mammaliamorpha) reveal a generalist diet

Stereoscopic microwear and 3D surface texture analyses on the cheek teeth of ten Upper Triassic to Lower Cretaceous tritylodontid (Mammaliamorpha) taxa of small/medium to large body size suggest that all were generalist feeders and none was a dietary specialist adapted to herbivory. There was no correspondence between body size and food choice. Stereomicroscopic microwear analysis revealed predominantly fine wear features with numerous small pits and less abundant fine scratches as principal components. Almost all analyzed facets bear some coarser microwear features, such as coarse scratches, large pits, puncture pits and gouges pointing to episodic feeding on harder food items or exogenous effects (contamination of food with soil grit and/or dust), or both. 3D surface texture analysis indicates predominantly fine features with large void volume, low peak densities, and various stages of roundness of the peaks. We interpret these features to indicate consumption of food items with low to moderate intrinsic abrasiveness and can exclude regular rooting, digging or caching behavior. Possible food items include plant vegetative parts, plant reproductive structures (seeds and seed-bearing organs), and invertebrates (i.e., insects). Although the tritylodontid tooth morphology and auto-occlusion suggest plants as the primary food resource, our results imply a wider dietary range including animal matter.

Maximum Bony Gape in Primates

Maximum jaw gape has important functional implications for behavior and feeding habits in primates. It has been suggested that gape is correlated to canine height and ingested food size. Extending these correlations to the fossil record would provide insights about the diets and/or social behavior of extinct primates. However, this can be problematic due to uncertainty about size and location of musculature, and it depends on reliability and repeatability of maximum gape estimation using only skeletal elements. In this study, maximum bony gape (MBG) was estimated using reliable landmarks and repeatable methods. The cranium was fixed in position and then the mandible was rotated and translated to the point immediately prior to loss of condyle-glenoid contact. Then it was photographed in a steady position using an adjustable wooden frame. This protocol allowed for photographs and linear measurements to be obtained for many museum specimens in a short time. The sample included 203 individuals, representing 42 species of primates. When scaled for body size, linear MBG correlates with maximum anesthetized gape (Hylander: Am J Phys Anthropol 150 (2013) 247-259), ingested food size (Perry and Hartstone-Rose: Am J Phys Anthropol 142 (2010) 625-635), and canine length but not condylar height. Anat Rec, 302:215-225, 2019. © 2018 Wiley Periodicals, Inc.

What did Hadropithecus eat, and why should paleoanthropologists care?

Over 40 years ago, Clifford Jolly noted different ways in which Hadropithecus stenognathus converged in its craniodental anatomy with basal hominins and with geladas. The Malagasy subfossil lemur Hadropithecus departs from its sister taxon, Archaeolemur, in that it displays comparatively large molars, reduced incisors and canines, a shortened rostrum, and thickened mandibular corpus. Its molars, however, look nothing like those of basal hominins; rather, they much more closely resemble molars of grazers such as Theropithecus. A number of tools have been used to interpret these traits, including dental microwear and texture analysis, molar internal and external morphology, and finite element analysis of crania. These tools, however, have failed to provide support for a simple dietary interpretation; whereas there is some consistency in the inferences they support, dietary inferences (e.g., that it was graminivorous, or that it specialized on hard objects) have been downright contradictory. Cranial shape may correlate poorly with diet. But a fundamental question remains unresolved: why do the various cranial and dental convergences exemplified by Hadropithecus, basal hominins, and Theropithecus exist? In this paper we review prior hypotheses regarding the diet of Hadropithecus. We then use stable carbon and nitrogen isotope data to elucidate this species' diet, summarizing earlier stable isotope analyses and presenting new data for lemurs from the central highlands of Madagascar, where Hadropithecus exhibits an isotopic signature strikingly different from that seen in other parts of the island. We offer a dietary explanation for these differences. Hadropithecus likely specialized neither on grasses nor hard objects; its staples were probably the succulent leaves of CAM plants. Nevertheless, aspects of prior hypotheses regarding the ecological significance of its morphology can be supported. Am. J. Primatol. 78:1098-1112, 2016. © 2015 Wiley Periodicals, Inc.

Controlled feeding trials with ungulates: a new application of in vivo dental molding to assess the abrasive factors of microwear

Microwear, the quantification of microscopic scratches and pits on the occlusal surfaces of tooth enamel, is a commonly used as a paleodietary proxy. For ungulates (hoofed mammals), scratch-dominant microwear distinguishes modern grazers from browsers, presumably as a result of abrasion from grass phytoliths (biogenic silica). However, it is also likely that exogenous grit (i.e., soil, dust) is a contributing factor to these scratch-dominant patterns, which may reflect soil ingestion that varies with feeding height and/or environmental conditions (e.g., dust production in open and/or arid habitats). This study assesses the contribution of exogenous grit to tooth wear by measuring the effects of fine- and medium-grained silica sand on tooth enamel using a novel live animal tooth molding technique. This study therefore constitutes the first controlled feeding experiment using ungulates and the first in vivo experiments using abrasives of different sizes. Four sheep were fed three diet treatments: 1) a mixture of Garrison and Brome hay (control), 2) hay treated with fine-grained silica sand (180–250 µm), and 3) hay treated with medium-grained silica sand (250–425 µm). We found a significant increase in pit features that was correlated with an increase in grain size of grit, corroborating earlier chewing simulation experiments that produced pits through grit-induced abrasion (i.e., the ‘grit effect’). Our results support an interpretation of large silica grains fracturing to create smaller, more abundant angular particles capable of abrasion, with jaw movement defining feature shape (i.e., scratch or pit).

Similar associations of tooth microwear and morphology indicate similar diet across marsupial and placental mammals

Low-magnification microwear techniques have been used effectively to infer diets within many unrelated mammalian orders, but the extent to which patterns are comparable among such different groups, including long extinct mammal lineages, is unknown. Microwear patterns between ecologically equivalent placental and marsupial mammals are found to be statistically indistinguishable, indicating that microwear can be used to infer diet across the mammals. Microwear data were compared to body size and molar shearing crest length in order to develop a system to distinguish the diet of mammals. Insectivores and carnivores were difficult to distinguish from herbivores using microwear alone, but combining microwear data with body size estimates and tooth morphology provides robust dietary inferences. This approach is a powerful tool for dietary assessment of fossils from extinct lineages and from museum specimens of living species where field study would be difficult owing to the animal’s behavior, habitat, or conservation status.

Dental topography indicates ecological contraction of lemur communities

Understanding the paleoecology of extinct subfossil lemurs requires reconstruction of dietary preferences. Tooth morphology is strongly correlated with diet in living primates and is appropriate for inferring dietary ecology. Recently, dental topographic analysis has shown great promise in reconstructing diet from molar tooth form. Compared with traditionally used shearing metrics, dental topography is better suited for the extraordinary diversity of tooth form among subfossil lemurs and has been shown to be less sensitive to phylogenetic sources of shape variation. Specifically, we computed orientation patch counts rotated (OPCR) and Dirichlet normal energy (DNE) of molar teeth belonging to 14 species of subfossil lemurs and compared these values to those of an extant lemur sample. The two metrics succeeded in separating species in a manner that provides insights into both food processing and diet. We used them to examine the changes in lemur community ecology in Southern and Southwestern Madagascar that accompanied the extinction of giant lemurs. We show that the poverty of Madagascar's frugivore community is a long-standing phenomenon and that extinction of large-bodied lemurs in the South and Southwest resulted not merely in a loss of guild elements but also, most likely, in changes in the ecology of extant lemurs.

Extinction and ecological retreat in a community of primates

The lemurs of Madagascar represent a prodigious adaptive radiation. At least 17 species ranging from 11 to 160 kg have become extinct during the past 2000 years. The effect of this loss on contemporary lemurs is unknown. The concept of competitive release favours the expansion of living species into vacant niches. Alternatively, factors that triggered the extinction of some species could have also reduced community-wide niche breadth. Here, we use radiocarbon and stable isotope data to examine temporal shifts in the niches of extant lemur species following the extinction of eight large-bodied species. We focus on southwestern Madagascar and report profound isotopic shifts, both from the time when now-extinct lemurs abounded and from the time immediately following their decline to the present. Unexpectedly, the past environments exploited by lemurs were drier than the protected (albeit often degraded) riparian habitats assumed to be ideal for lemurs today. Neither competitive release nor niche contraction can explain these observed trends. We develop an alternative hypothesis: ecological retreat, which suggests that factors surrounding extinction may force surviving species into marginal or previously unfilled niches.

The Hadropithecus conundrum reconsidered, with implications for interpreting diet in fossil hominins

The fossil 'monkey lemur' Hadropithecus stenognathus has long excited palaeontologists because its skull bears an astonishing resemblance to those of robust australopiths, an enigmatic side branch of the human family tree. Multiple lines of evidence point to the likelihood that these australopiths ate at least some 'hard', stress-limited food items, but conflicting data from H. stenognathus pose a conundrum. While its hominin-like craniofacial architecture is suggestive of an ability to generate high bite forces, details of its tooth structure suggest that it was not well equipped to withstand the forces imposed by cracking hard objects. Here, we use three-dimensional digital reconstructions and finite-element analysis to test the hard-object processing hypothesis. We show that Archaeolemur sp. cf. A. edwardsi, a longer-faced close relative of H. stenognathus that lacked hominin convergences, was probably capable of breaking apart large, stress-limited food items, while Hadropithecus was better suited to processing small, displacement-limited (tougher but more compliant) foods. Our suggestion that H. stenognathus was not a hard-object feeder has bearing on the interpretation of hominin cranial architecture; the features shared by H. stenognathus and robust australopiths do not necessarily reflect adaptations for hard-object processing.

Comparing Dirichlet normal surface energy of tooth crowns, a new technique of molar shape quantification for dietary inference, with previous methods in isolation and in combination

Inferred dietary preference is a major component of paleoecologies of extinct primates. Molar occlusal shape correlates with diet in living mammals, so teeth are a potentially useful structure from which to reconstruct diet in extinct taxa. We assess the efficacy of Dirichlet normal energy (DNE) calculated for molar tooth surfaces for reflecting diet. We evaluate DNE, which uses changes in normal vectors to characterize curvature, by directly comparing this metric to metrics previously used in dietary inference. We also test whether combining methods improves diet reconstructions. The study sample consisted of 146 lower (mandibular) second molars belonging to 24 euarchontan taxa. Five shape quantification metrics were calculated on each molar: DNE, shearing quotient, shearing ratio, relief index, and orientation patch count rotated (OPCR). Statistical analyses were completed for each variable to assess effects of taxon and diet. Discriminant function analysis was used to assess ability of combinations of variables to predict diet. Values differ significantly by diets for all variables, although shearing ratios and OPCR do not distinguish statistically between insectivores and folivores or omnivores and frugivores. Combined analyses were much more effective at predicting diet than any metric alone. Alone, relief index and DNE were most effective at predicting diet. OPCR was the least effective alone but is still valuable as the only quantitative measure of surface complexity. Of all methods considered, DNE was the least methodologically sensitive, and its effectiveness suggests it will be a valuable tool for dietary reconstruction.

Tooth size variation related to age in Amboseli baboons

We measured the molar size from a single population of wild baboons from Amboseli (Kenya), both females (n=57) and males (n=50). All the females were of known age; the males represented a mix of known-age individuals (n=31) and individuals with ages estimated to within 2 years (n=19). The results showed a significant reduction in the mesiodistal length of teeth in both sexes as a function of age. Overall patterns of age-related change in tooth size did not change whether we included or excluded the individuals of estimated age, but patterns of statistical significance changed as a result of changed sample sizes. Our results demonstrate that tooth length is directly related to age due to interproximal wearing caused by M2 and M3 compression loads. Dental studies in primates, including both fossil and extant species, are mostly based on specimens obtained from osteological collections of varying origins, for which the age at death of each individual in the sample is not known. Researchers should take into account the phenomenon of interproximal attrition leading to reduced tooth size when measuring tooth length for ondontometric purposes.

Evidence for dietary niche separation based on infraorbital foramen size variation among subfossil lemurs

The size of the infraorbital foramen (IOF) has been used in drawing both phylogenetic and ecological inferences regarding fossil taxa. Within the order Primates, frugivores have relatively larger IOFs than folivores or insectivores. This study uses relative IOF size in lemurs to test prior trophic inferences for subfossil lemurs and to explore the pattern of variation within and across lemur families. The IOFs of individuals belonging to 12 extinct lemur species were measured and compared to those of extant Malagasy strepsirhines. Observations matched expectations drawn from more traditional approaches (e.g. dental morphology and microwear, stable isotope analysis) remarkably well. We confirm that extinct lemurs belonging to the families Megaladapidae and Palaeopropithecidae were predominantly folivorous and that species belonging to the genus Pachylemur (Lemuridae) were frugivores. Very high values for relative IOF area in Archaeolemur support frugivory but are also consistent with omnivory, as certain omnivores use facial touch cues while feeding. These results provide additional evidence that the IOF can be used as an informative osteological feature in both phylogenetic and paleoecological interpretations of the fossil record.

"Life history space": a multivariate analysis of life history variation in extant and extinct Malagasy lemurs

Studies of primate life history variation are constrained by the fact that all large-bodied extant primates are haplorhines. However, large-bodied strepsirrhines recently existed. If we can extract life history information from their skeletons, these species can contribute to our understanding of primate life history variation. This is particularly important in light of new critiques of the classic "fast-slow continuum" as a descriptor of variation in life history profiles across mammals in general. We use established dental histological methods to estimate gestation length and age at weaning for five extinct lemur species. On the basis of these estimates, we reconstruct minimum interbirth intervals and maximum reproductive rates. We utilize principal components analysis to create a multivariate "life history space" that captures the relationships among reproductive parameters and brain and body size in extinct and extant lemurs. Our data show that, whereas large-bodied extinct lemurs can be described as "slow" in some fashion, they also varied greatly in their life history profiles. Those with relatively large brains also weaned their offspring late and had long interbirth intervals. These were not the largest of extinct lemurs. Thus, we distinguish size-related life history variation from variation that linked more strongly to ecological factors. Because all lemur species larger than 10 kg, regardless of life history profile, succumbed to extinction after humans arrived in Madagascar, we argue that large body size increased the probability of extinction independently of reproductive rate. We also provide some evidence that, among lemurs, brain size predicts reproductive rate better than body size.

Ontogeny and phyletic size change in living and fossil lemurs

Lemurs are notable for encompassing the range of body-size variation for all primates past and present-close to four orders of magnitude. Benefiting from the phylogenetic proximity of subfossil lemurs to smaller-bodied living forms, we employ allometric data from the skull to probe the ontogenetic bases of size differentiation and morphological diversity across these clades. Building upon prior pairwise comparisons between sister taxa, we performed the first clade-wide analyses of craniomandibular growth allometries in 359 specimens from 10 lemuroids and 176 specimens from 8 indrioids. Ontogenetic trajectories for extant forms were used as a criterion of subtraction to evaluate morphological variation, and putative adaptations among sister taxa. In other words, do species-level differences in skull form result from the differential extension of common patterns of relative growth?In lemuroids, a pervasive pattern of ontogenetic scaling is observed for facial dimensions in all genera, with three genera also sharing relative growth trajectories for jaw proportions (Lemur, Eulemur, Varecia). Differences in masticatory growth and form characterizing Hapalemur and fossil Pachylemur likely reflect dietary factors. Pervasive ontogenetic scaling characterizes the facial skull in extant Indri, Avahi, and Propithecus, as well as their larger, extinct sister taxa Mesopropithecus and Babakotia. Significant interspecific differences are observed in the allometry of indrioid masticatory proportions, with variation in the mechanical advantage of the jaw adductors and stress-resisting elements correlated with diet. As the growth series and adult data are largely coincidental in each clade, interspecific variation in facial form may result from selection for body-size differentiation among sister taxa. Those cases where trajectories are discordant identify potential dietary adaptations linked to variation in masticatory forces during chewing and biting. Although such dissociations highlight selection to uncouple shared ancestral growth patterns, they occur largely via transpositions and retention of primitive size-shape covariation patterns or relative growth coefficients.

Possible fruit protein effects on primate communities in madagascar and the neotropics

BACKGROUND

The ecological factors contributing to the evolution of tropical vertebrate communities are still poorly understood. Primate communities of the tropical Americas have fewer folivorous but more frugivorous genera than tropical regions of the Old World and especially many more frugivorous genera than Madagascar. Reasons for this phenomenon are largely unexplored. We developed the hypothesis that Neotropical fruits have higher protein concentrations than fruits from Madagascar and that the higher representation of frugivorous genera in the Neotropics is linked to high protein concentrations in fruits. Low fruit protein concentrations in Madagascar would restrict the evolution of frugivores in Malagasy communities.

METHODOLOGY/PRINCIPAL FINDINGS

We reviewed the literature for nitrogen concentrations in fruits from the Neotropics and from Madagascar, and analyzed fruits from an additional six sites in the Neotropics and six sites in Madagascar. Fruits from the Neotropical sites contain significantly more nitrogen than fruits from the Madagascar sites. Nitrogen concentrations in New World fruits are above the concentrations to satisfy nitrogen requirements of primates, while they are at the lower end or below the concentrations to cover primate protein needs in Madagascar.

CONCLUSIONS/SIGNIFICANCE

Fruits at most sites in the Neotropics contain enough protein to satisfy the protein needs of primates. Thus, selection pressure to develop new adaptations for foods that are difficult to digest (such as leaves) may have been lower in the Neotropics than in Madagascar. The low nitrogen concentrations in fruits from Madagascar may contribute to the almost complete absence of frugivorous primate species on this island.

Geometric morphometric investigation of molar shape diversity in modern lemurs and lorises

In the study of mammalian adaptation to the environment, teeth are of primary importance due to their role as one of the direct interaction points between an individual and its ecological surroundings. Here, molar shape and function are investigated through traditional multivariate statistics and Thin-Plate Splines deformations to compare the relative location of lower first molar occlusal structures (protoconid, metaconid, hypoconid, entoconid, cristid obliqua, and protolophid) in modern lemurs, lorises, tarsiers, and a non-primate outgroup taxon (Tupaia). Results suggest that shape is based both on tooth size and dietary patterns. Small teeth tend to be short (anteroposteriorally) with wide talonids, whereas larger teeth are generally characterized as being long and narrow. In considering non-size related shape trends, frugivorous and graminivorous taxa generally exhibit a relatively buccal intersection of the cristid obliqua with the base of the protolophid, and a relatively "perpendicular" position of the protolophid in relation to the anteroposterior axis of the tooth (defined as the axis connecting the protolophid and hypoconid). Morphological trends of folivores include a central (midline) position of the cristid obliqua-protolophid base intersection and an oblique angle of the protolophid. Insectivorous taxa (primate and non-primate) generally exhibit a central placement of the cristid obliqua-protolophid base intersection (as in folivores), along with a relatively perpendicular angle of the protolophid (as in frugivores). Omnivorous taxa exhibit shape patterns that are intermediate between these three former groups. This study provides a comparative baseline for the interpretation of morphological trends in fossil primate groups, particularly the Adapiformes.

Relief index of second mandibular molars is a correlate of diet among prosimian primates and other euarchontan mammals

This study describes and tests a new method of calculating a shape metric known as the relief index (RFI) on lower second molars of extant euarchontan mammals, including scandentians (treeshrews), dermopterans (flying lemurs), and prosimian primates (strepsirhines and tarsiers). RFI is the ratio of the tooth crown three-dimensional area to two-dimensional planar area. It essentially expresses hypsodonty and complexity of tooth shape. Like other measurements of complexity, RFI ignores taxon-specific features, such as certain cusps and crests, which are usually considered in more traditional studies of tooth function. Traditional statistical analyses of the study sample show that RFI distinguishes taxa with differing amounts of structural carbohydrates in their diets, with frugivore/gramnivores being significantly lower in RFI than omnivores, and insectivores/folivores being significantly higher in RFI than the other two. Information on absolute size, or body mass, is needed to reliably parse out insectivores and folivores; however, if the study sample is limited to Primates, RFI alone distinguishes many folivores (lower) from insectivores (higher). Finally, phylogenetically independent contrasts of RFI and dietary preference are strongly correlated with one another, indicating that variance in RFI is better explained by dietary diversity than phylogenetic affinity in this sample. Because of the accuracy and phylogenetic insensitivity of the RFI among Euarchonta, this method can be applied to fossil primates and stem-primates (plesiadapiforms) and used to elucidate and compare their dietary preferences. Such comparisons are important for developing a more detailed view of primate evolution.

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.

Do mandibular cross-sectional properties and dental microwear give similar dietary signals?

Previous animal experimental work evaluating the effects of dietary consistency on mastication was generally limited to studies of either mandibular structure or rates and types of tooth wear. Control groups fed hard diets (HD) consistently exhibited increased cortical remodeling and/or bone strength when compared to groups fed soft diets (SD). Results of tooth-wear studies showed faster rates of tooth wear in HD animals. This study evaluates the effects of dietary differences on both mandibular structural morphology and postcanine dental microwear in the same animals. We examined mandibles and dentitions from eight miniature swine, raised from 4 weeks to 9 months of age on HD and SD (n = 4, each group). Mandibular structural properties were calculated from peripheral quantitative computed tomography slices at the dp3-dp4 and dp4-M1 junctions. Dental microwear analysis was performed on mandibular lingual crushing facets of dp4 and M1, using photomicrographs of high-resolution casts taken at 500x magnification in a scanning electron microscope. Our results suggest that between the dp3-dp4 contact, HD animals have mandibles that are stronger and more rigid mediolaterally than SD animals. At the dp4-M1 contact, HD animals have mandibles that are stronger and more rigid mediolaterally, dorsoventrally, and in torsion than SD animals. Dental microwear results indicate that SD pigs have higher incidences of pitting and more overall microwear features on their premolars than do HD pigs, yet there are no significant differences in molar microwear morphology between the dietary groups. Near-significant correlations exist between pit size and dorsoventral bending strength, but only for HD pigs. These results suggest that dietary consistency significantly affects both mandibular structure and dental microwear, yet direct correlations between the two are complicated by a number of factors.

The evolution of extinction risk: past and present anthropogenic impacts on the primate communities of Madagascar

There are two possible approaches to understanding natural and human-induced changes in the primate communities of Madagascar. One is to begin with present-day and recent historic interactions and work backwards. A second is to begin with paleoecological records of Malagasy primate communities before and immediately following human arrival, and the associated evidence of human and nonhuman primate interactions, and work forwards. On the basis of biological and climatic studies, as well as historic and ethnohistoric records, we are beginning to understand the abiotic and biotic characteristics of Madagascar's habitats, the lemurs' ecological adaptations to these unique habitats, the extent of forest loss, fragmentation and hunting, and the differential vulnerability of extant lemur species to these pressures. On the basis of integrated paleoecological, archaeological and paleontological research, we have begun to construct a detailed chronology for late prehistoric Madagascar. We are beginning to understand the complex sequence of events that led to one of the most dramatic recent megafaunal extinction/extirpation events. Combining the perspectives of the past and the present, we see a complex set of interactions affecting an initially rich but vulnerable fauna. The total evidence refutes any simple, unicausal (e.g. hunting/habitat destruction/climate change) explanation of megafaunal extinctions, yet unequivocally supports a major role--both direct and indirect--for humans as the trigger of the extinction process. It also supports a change over time in the relative importance of hunting versus habitat loss, and in the trophic characteristics of the primate communities in Madagascar.

Dental microwear texture analysis: technical considerations

Dental microwear analysis is commonly used to infer aspects of diet in extinct primates. Conventional methods of microwear analysis have usually been limited to two-dimensional imaging studies using a scanning electron microscope and the identification of apparent individual features. These methods have proved time-consuming and prone to subjectivity and observer error. Here we describe a new methodological approach to microwear: dental microwear texture analysis, based on three-dimensional surface measurements taken using white-light confocal microscopy and scale-sensitive fractal analysis. Surface parameters for complexity, scale of maximum complexity, anisotropy, heterogeneity, and textural fill volume offer repeatable, quantitative characterizations of three-dimensional surfaces, free of observer measurement error. Some results are presented to illustrate how these parameters distinguish extant primates with different diets. In this case, microwear surfaces of Cebus apella and Lophocebus albigena, which consume some harder food items, have higher average values for complexity than do folivores or soft fruit eaters.