Cross-sectional geometric properties of the Otavipithecus mandible

Cross-sectional geometric properties of the postcanine mandibular corpus are determined for the only known specimen of Otavipithecus namibiensis, a middle Miocene hominoid from southern Africa. It is shown that Otavipithecus is unique in that several important mechanical properties of its mandible, including maximum and minimum moments of inertia and distribution of cortical bone, differ from patterns seen in both extant hominoids and the early hominids Australopithecus africanus and Australopithecus (Paranthropus) robustus. This is particularly apparent in the mechanical design of the posterior portion of the mandibular corpus for resisting increased torsional and transverse bending moments. Cortical index values at the level of M₂ also reveal that both Otavipithecus and A. africanus are similarly designed to resist increased masticatory loads with relatively less cortical bone area, a highly efficient mechanical design. © 1996 Wiley-Liss, Inc.     

Mandibular morphology and diet in the genusCebus

The influence of hard-object feeding on the size and shape of the mandibular corpus was investigated through a comparative biomechanical analysis of the jaws of adult femaleCebus apella andCebus capucinus. Computed tomography (CT) was used to discern the amount and distribution of cortical bone at M₂ and symphyseal cross sections. From these data, the biomechanical properties of the mandibular corpus were determined to assess the structural rigidity of the jaw with respect to the bending, torsional, and shear stresses that occur during mastication and incision. The mandibles ofC. apella are demonstrably more robust than those ofC. capucinus in terms of biomechanical rigidity; differences in corporeal size rather than shape largely account for the enhanced robusticity in the sample ofC. apella. The differences that separate the two taxa probably represent a structural response to the mechanical demands of durophagy inC. apella. These observations suggest that specialization on a diet of hard objects may be expected to result in an overall hypertrophy of bony contours throughout the mandibular corpus.     

The enigmatic molar from Gondolin, South Africa: Implications for Paranthropus paleobiology

The specific attribution of the large hominin M₂ (GDA-2) from Gondolin has significant implications for the paleobiology of Paranthropus. If it is a specimen of Paranthropus robustus it impacts that species' size range, and if it belongs to Paranthropus boisei it has important biogeographic implications. We evaluate crown size, cusp proportions and the likelihood of encountering a large-bodied mammal species in both East and South Africa in the Early Pleistocene. The tooth falls well outside the P. robustus sample range, and comfortably within that for penecontemporaneous P. boisei. Analyses of sample range, distribution and variability suggest that it is possible, albeit unlikely to find a M₂ of this size in the current P. robustus sample. However, taphonomic agents - carnivore (particularly leopard) feeding behaviors - have likely skewed the size distribution of the Swartkrans and Drimolen P. robustus assemblage. In particular, assemblages of large-bodied mammals accumulated by leopards typically display high proportions of juveniles and smaller adults. The skew in the P. robustus sample is consistent with this type of assemblage. Morphological evidence in the form of cusp proportions is congruent with GDA-2 representing P. robustus rather than P. boisei. The comparatively small number of large-bodied mammal species common to both South and East Africa in the Early Pleistocene suggests a low probability of encountering an herbivorous australopith in both. Our results are most consistent with the interpretation of the Gondolin molar as a very large specimen of P. robustus. This, in turn, suggests that large, presumptive male, specimens are rare, and that the levels of size variation (sexual dimorphism) previously ascribed to this species are likely to be gross underestimates.     

Ontogenetic features of <Emphasis Type="Italic">Dolichopithecus</Emphasis> (Primates,Colobidae) from the Pliocene of Pridnestrovie

In the permanent dentition of the extinct genus Dolichopithecus, M₁, I₁, and I₂ were the first to erupt, followed by M₂, canine, P₄, and P₃. M₃ was the last permanent tooth to erupt. At the stage of eruption of P₄ and P₃, M₃ was incompletely mineralized. The difference from the extant Cercopithecoidea is the loss of all deciduous teeth after eruption of incisors and M1 and the similarity is observed in the succession of eruption of permanent teeth. In Dolichopithecus, the lower jaw body retained constant in thickness after eruption of M₂. The lower jaw increased in length and depth, as the horizontal ramus grew with the formation and eruption of M₃.     

Further analysis of mandibular molar crown and cusp areas in Pliocene and early Pleistocene hominids

Crown and cusp areas of mandibular molars were measured and analyzed on a sample of 249 specimens attributed to Australopithecus afarensis, A. africanus, A. (Paranthropus) robustus, A. (P.) boisei, and early Homo. In addition to intertaxon comparisons, we compared data that had been collected independently by two of the authors using methods that differ slightly in technique of measurement. Interobserver differences were evaluated by the t-test of paired comparisons, method error statistic, percent differences, and principal component analysis. Results suggest that between-technique error of measurement of overall crown area is small. Error estimates for individual cusp area measurements were of larger relative magnitude. However, these were not sufficient to detract from the conclusions derived from comparative analyses. Our results are in general agreement with previous assessments of early hominid dental size. Crown areas of A. africanus, however, exhibit a mosaic pattern, with M1 similar in size to that of A. afarensis and early Homo, and M2 and M3 similar in size to that of A. robustus. Intertaxon comparisons of relative cusp area were undertaken by univariate statistics and principal component analysis. These analyses revealed that while A. (P.) robustus and A. (P.) boisei both possess mandibular molars with cusp proportions significantly different from the ‘non-robust’ taxa, these differences are substantially greater in A. (P.) boisei. © 1994 Wiley-Liss, Inc.     

Hominid-pongid distinctiveness in the miocene-pliocene fossil record: The lothagam mandible

The Lothagam mandibular fragment, found in 1967 west of Lake Turkana, Kenya, has been dated to 5.5 million years ago. This date is significant because it may lie within the suggested time range during which the hominid and pongid clades diverged. Because of its fragmentary condition and great age, this specimen has run the gamut of taxonomic assignations, from ramapithecine to pongid to hominid. These three nomenclatural categories serve as the basis for three hypotheses tested in this study. First, morphological and metric comparisons between Lothagam and a sample of Euroafrican ramapithecines address the hypothesis of “Lothagam as predi-vergence hominoid.” Second, comparisons with a sample of Pan test the “Lothagam as postdivergence, African protopongid” hypothesis. Finally, samples of Australopithecus afarensis and A. africanus were utilized to evaluate the hypothesis of “Lothagam as postdivergence, early hominid.” Unlike previous studies attempting to ascertain the evolutionary affinities of this enigmatic fossil, this work benefits from the large sample of A. afarensis specimens now generally available for study. Metric and morphological comparisons demonstrate Lothagam's affinity to A. afarensis in sharing derived, hominid states in such features as the mental foramen vertical position, the ascending ramus origin, the breadth of the alveolar margin, the reduction of the hypoconulid, the dimensions of the M₁ and the dimensions of the mandibular corpus. It is suggested that the dental/gnathic features enumerated in this study can be employed to distinguish ancestral hominid from pongid in future Mio/Pliocene paleontological discoveries.     

Sexual dimorphism in mandibular growth of French-Canadian children 6 to 10 years of age

Polynomial regression is used to model the mandibular growth of 28 girls and 26 boys who were followed longitudinally from 6 to 10 years of age. The pooled-within individual designs indicate that ramus height follows a linear pattern of size increase; corpus and total mandibular lengths display curvilineal, decelerating, patterns of growth over the age range. Multivariate analyses of variance reveal significant sex differences in size, favoring boys, for the two length measures at 6 years of age. Growth velocity for corpus length is also significantly greater in boys than in girls. Sexual dimorphism in the growth of total mandibular length is more complex, including differences in velocity and deceleration. Ramus height shows no significant pattern of variation between boys and girls for either size or growth velocity.     

Cross-sectional Bone Distribution in the Mandibles of Gouging and Non-gouging Platyrrhini

Recent morphometric analyses have led to dissimilar conclusions about whether the jaws of tree-gouging primates are designed to resist the purportedly large forces generated during this biting behavior. We further address this question by comparing the cross-sectional geometry of the mandibular corpus and symphysis in tree-gouging common marmosets (Callithrix jacchus) to nongouging saddleback tamarins (Saguinus fuscicollis) and squirrel monkeys (Saimiri sciureus). As might be expected, based on size, squirrel monkeys tend to have absolutely larger cross-sectional areas at each tooth location sampled, while saddleback tamarins are intermediate, followed by the smaller common marmosets. Similarly, the amount and distribution of cortical bone in squirrel monkey jaws provides them with increased ability to resist sagittal bending (I _xx ) and torsion (K) in the corpus as well as coronal bending (I _xx ) and shearing in the symphysis. However, when the biomechanical parameters are scaled to respective load arm estimates, there are few significant differences in relative resistance abilities among the 3 species. A power analysis indicates that we cannot statistically rule out subtle changes in marmoset jaw form linked to resisting loads during gouging. Nevertheless, our results correspond to studies in vivo of jaw loading, field data, and other comparative analyses suggesting that common marmosets do not generate relatively large bite forces during tree gouging. The 3 species are like most other anthropoids in having thinner bone on the lingual than on the buccal side of the mandibular corpus at M₁. The similarity in corporal shape across anthropoids supports a hypothesized stereotypical pattern of jaw loading during chewing and may indicate a conserved pattern of mandibular growth for the suborder. Despite the overall similarity, platyrrhines may differ slightly from catarrhines in the details of their cortical bone distribution.

Coexistence of the predatory cyclopoids Acanthocyclops robustus (Sars) and Mesocyclops leuckarti (Claus) in a small eutrophic lake

The coexistence of two common species of predatory cyclopoid copepods, Acanthocyclops robustus and Mesocyclops leuckarti, in a small, eutrophic lake was studied. Both species are of similar size, inhabit the same water layers and have similar seasonal occurrence. A. robustus shows faster embryonic and postembryonic development and produces bigger clutches. Ingestion rates of A. robustus are higher than in M. leuckarti, especially with large prey types and low temperatures. Females of A. robustus are heavily preyed upon by fish. This predation pressure leads to extremely skewed sex ratios, which are unfavourable to population growth. A. robustus is therefore, on balance, favoured in productive lakes. Dominance over M. leuckarti is, however, less clear in warmer years.     

Relationship between canine dimorphism and mandibular morphology in the hamadryas baboon and the Japanese monkey

To examine morphological interrelationships between canine size and mandibular corpus shape, inter-sex comparisons were made in the hamadryas baboon and the Japanese monkey, known to display extreme and moderate canine dimorphism, respectively. Results of adult comparisons showed that all mandibular dimensions were significantly larger in the males than in the females in both species. In the hamadryas baboon, the males also exhibited a higher ratio of anterior to posterior corpus height than the females. This sex difference in corpus shape was not significant in the Japanese monkey, indicating lack of involvement of canine dimorphism. Analysis of mandibular growth patterns in the hamadryas baboon demonstrated that significant sexual size difference did not occur before incisor eruption, and that the anteriorly high corpus of the adult male mandible was associated with a rapidly increasing symphyseal height after incisor eruption. It was also shown that the female canine started to erupt shortly after incisor eruption, while the forming male canine continued to stay near the mandibular base and developed further in size until eruption. The relative positions of the incisors kept shifting upwards even after eruption in the males, while they hardly changed in the females. It is therefore suggested that the prolonged development and size increase of the male canine is accompanied by further enlargement of the symphysis, resulting in the higher anterior corpus of the adult males compared to the adult females. The results thus indicate the importance of understanding the spatial relationships of the developing teeth in interpreting mandibular morphology.     

Bone remodeling of the Homo heidelbergensis mandible; the Atapuerca-SH sample.

Growth by bone remodeling is one of the key mechanisms responsible for skeletal morphology. This mechanism consists of the coordinated activity of two cellular groups: osteoblasts and osteoclasts, which are responsible for bone deposition and resorption, respectively. Information obtained from the study of these remodeling growth fields allows us to understand how species-specific craniofacial form is achieved. These data can help to explain the facial growth differences among Primates, both extinct and extant. The aim of this study was to obtain the distribution of growth remodeling fields of the Homo heidelbergensis mandible (Atapuerca-SH sample), and to infer the growth processes responsible for its specific morphology. A Reflected Light Microscope (RLM) was used to identify the microfeatures of the bone surface related to bone deposition and resorption. Results show that H. heidelbergensis presents a specific growth field distribution, which differs slightly between immature and adult individuals. Interpretation of these maps indicates that the mandible of H. heidelbergensis presents noteworthy variability in the symphyseal region. Two distinct patterns of growth are seen, one of those unique for this species and the other similar to that of Homo sapiens. The lingual side of the mandibular corpus has a resorption area found only in this species and one that includes a variable extension in immature and adult individuals. Finally, the mandibular ramus is characterized, among other aspects, by a large resorption field on its buccal surface. Considering the mandible as a whole, the bone remodeling pattern obtained in this work shows that lower facial growth in H. heidelbergensis is dominated mainly by forward growth, illustrated by the strong inward displacement of the ramus, which is in agreement with the Enlow's “V” growth principle.     

Prohylobates (Primates) from the Early Miocene of Libya: A new species and its implications for cercopithecid origins

Prohylobates simonsi n. sp. is described on the basis of a partial mandible with M_2–3 from the region of GebelZelten. It is nearly twice the size of the penecontemporaneous P. tandyi and has a relatively longer M₃, but otherwise is nearly identical in morphology. Prohylobates is the most conservative known cercopithecid, presenting incomplete bilophodonty, possible cingulum remnants, high relative width of M₂ and robust mandibular corpus. The variation in M₃ length is comparable to that within some later cercopithecid species and between the species of Propliopithecus, the Oligocene catarrhine suggested to be nearest the ancestry of the Cercopithecidae. Parapithecus (including Simonsius) is not a cercopithecid ancestor     

Phylogenetic signal,function and integration in the subunits of the carnivoran mandible

Complex phenotypes could be interpreted as the result of functional integration between identifiable subunits. Common developmental or ecological factors may favour macroevolutionary morphological integration so that functional subunits also covary above the species level. We investigate shape variation and functional integration in two subunits of the mammalian mandible: the corpus and the ramus in a subset of extant terrestrial Carnivora using geometric morphometric and comparative methods. More specifically, we test if corpus and ramus shape exhibit similar degree of homoplasy and if these traits covary above species level. Additionally, broad functional categorisations (predaceous and non predaceous) are investigated to test if differences in morphological variation and integration at macroevolutionary scale occur. Principal components of shape data show a significant phylogenetic signal in both mandibular subunits, with the ramus exhibiting a higher degree of homoplasy than the corpus. Functional groups (predators and non-predators) are significantly distinct in corpus shape, while in the ramus significance emerges only after removing the phylogenetic signal. Partial Least Square shows that mandibular corpus and ramus region covaries above species level even if this trend is not supported when employing comparative methods. Only in a subset of predaceous species covariation still hold. We conclude that mandibular subunits of Carnivora differ considerably in shape among predaceous and non-predaceous species because of the adaptive selection pressure imposed by catching and hold of live prey. This selective process also favoured macroevolutionary integration in predaceous carnivorans.     

Population variation in tooth, jaw, and root size: a radiographic study of two populations in a high-attrition environment

Radiographs were taken of the jaws of skeletal remains of two populations of different-phenotype Prehistoric Australians from Roonka and Early New Zealanders (Maoris). On these radiographs crown, root, and corpus size were measured. Corpus height was subdivided into alveolar bone height, defined as the bone superior to the mandibular canal, and basal bone height, defined as that inferior to the mandibular canal. Both between and within the two populations there was a significant and negative correlation between crown size and corpus height. The differences between the two populations in corpus height were associated with differences in alveolar bone height rather than basal bone height and support hypotheses associating continued eruption of adult teeth with growth of the alveolar bone. The findings also support previous studies that have shown only a low correlation between crown size, root size, and corpus height.     

Taxonomic and functional implications of mandibular scaling in early hominins

Body mass estimates for fossil hominin taxa can be obtained from suitable postcranial and cranial variables. However, the nature of the taphonomic processes that winnow the mammalian fossil record are such that these data are usually only available for the minority of the specimens that comprise the hypodigm of a species. This study has investigated the link between species mean body mass and the height and width of the mandibular corpus in a core sample of 23 species of extant simians. The slopes of the least-squares regressions for the whole sample and for the hominoid subset are similar. However, the intercepts differ so that for a given body mass, a hominoid will generally have a smaller mandible than a generalized simian. The same mandibular measurements were taken on 75 early hominin mandibles assigned to eight species groups. When mandibular corpus height- and width-derived estimates of body mass for the fossil taxa were compared with available postcranial and cranial-derived body mass estimates, the eight early hominin species sort into four groups. The first, which includes A. afarensis and A. africanus, has mandibles which follow a “generalized simian” scaling relationship. The second group, which comprises the two “robust” australopithecine species, P. boisei and P. robustus, has mandibles which scale with body mass as if they are “super-simians,” for they have substantially larger mandibles than a simian with the same body mass. The two “early Homo” species, H. habilis sensu stricto and H. rudolfensis, make up the third group. It has mandibular scaling relationships that are intermediate between that of the comparative simian sample and that of the hominoid subsample. The last of the four groups comprises H. ergaster and H. erectus; their mandibles scale with body mass as if they were hominoids, so that of the four groups they have the smallest mandibles per unit body mass. These results are related to comparable information about relative tooth size. Their relevance for attempts to interpret the dietary adaptations of early hominins are explored. Am J Phys Anthropol 105:523–538, 1998. © 1998 Wiley-Liss, Inc.     

Cranial adaptation to a high attrition diet in Japanese macaques

Primates with diets that require greater occlusal forces to process exhibit anteroposteriorly shorter, vertically deeper faces, more anteriorly placed masseter attachment areas, and broader, taller mandibular corpora compared to closely related species/populations. Japanese macaques (Macaca fuscata)eat different, perhaps mechanically tougher to process, foods than other macaques do. Accordingly, they should exhibit structural features of the skull related to dissipating great occlusal loads. To test this hypothesis I compared cranial variables amongst wild-caught, adult female skulls (n = 85) of M. fuscataand three other macaque species (M. mulatta, M. fascicularis,and M. nemestrina)and applied least-squares and reduced-major-axis regression analysis and principal components analysis (PCA) to 17 cranial variables reflecting facial, vault, and mandibular dimensions. When scaled for size, the Japanese macaque has a vertically deeper and anteroposteriorly shorter face,a broader but not taller mandibular corpus, and a more anteriorly placed masseter muscle than the other three macaques do. The first PCA axis isolates variation due to a suite of characters related to mechanical efficiency in dissipating occlusal loads (vertically deep face and broad corpus) and differentiates the Japanese macaques from the other species. This, coupled with reported dietary differences among species, suggests that Japanese macaques are selected for dissipating greater occlusal loads than other macaques are. The presence of a narrow mandible relative to cranial breadth and a hyperrobust mandibular corpus width suggests that axial torsion is a significant influence in the masticatory regime of M. fuscata.The lack of an increase in corpus height indicates that parasagittal bending is not as significant an influence. Geographic and climatic influences cannot account for the patterns of variation between M. fuscataand the other macaques.     

The influence of non‐climate predictors at local and landscape resolutions depends on the autecology of the species

Species distribution models have come under criticism for being too simplistic for making robust future forecasts, partly because they assume that climate is the main determinant of geographical range at large spatial extents and coarse resolutions, with non‐climate predictors being important only at finer scales. We suggest that this paradigm might be obscured by species movement patterns. To explore this we used contrasting kangaroo (family Macropodidae) case studies: two species with relatively small, stable home ranges (Macropus giganteus and M. robustus) and three species with more extensive, adaptive ranging behaviour (M. antilopinus, M. fuliginosus and M. rufus). We predicted that non‐climate predictors will be most influential to model fit and predictive performance at local spatial resolution for the former species and at landscape resolution for the latter species. We compared residuals autocovariate – boosted regression tree (RAC‐BRT) model statistics with and without species‐specific non‐climate predictors (habitat, soil, fire, water and topography), at local‐ and landscape‐level spatial resolutions (5 and 50 km). As predicted, the influence of non‐climate predictors on model fit and predictive performance (compared with climate‐only models) was greater at 50 compared with 5 km resolution for M. rufus and M. fuliginosus and the opposite trend was observed for M. giganteus. The results for M. robustus and M. antilopinus were inconclusive. Also notable was the difference in inter‐scale importance of climate predictors in the presence of non‐climate predictors. In conclusion, differences in autecology, particularly relating to space use, may contribute to the importance of non‐climate predictors at a given scale, not model scale per se. Further exploration of this concept across a range of species is encouraged and findings may contribute to more effective conservation and management of species at ecologically meaningful scales.     

Differences in molar wear gradient between adult macaques and langurs

Interspecific differences in the amount and form of molar wear in nonhuman primates are only beginning to be documented and understood. The purpose of this study was to look at the wear gradient between M₁ and M₂ in a sample of macaques and langurs to determine if differences in wear gradient could be related to differences in diet. A skeletal collection of wild shot Macaca fascicularis, Presbytis cristata, and Presbytis rubicunda from the Museum of Comparative Zoology at Harvard University was examined using photogrammetric techniques. X, Y, and Z coordinates were used to compute areas of dentin exposure on the buccal occlusal surfaces of M₁ and M₂. The relationship between these variables was examined using Bartlett’s three-group method and least-squares regression. Interspecific comparisons of the resultant y intercepts indicate that (I) M. fascicularis (as compared with P. cristata or P.) has more dentin exposed on M₁ when there is none exposed on M₂, and (2) P. cristata (as compared with P. rubicunda) has more dentin exposed on M₁ when there is none exposed on M₂. Factors that might be responsible for these differences are (a) differences in dentin/enamel structure, (b) differences in molar eruption timing, and (c) differences in behavior. An unusual intercusp sequence of dentin exposure in the langurs makes precise interpretations difficult. However, at the present time, behavioral differences among the species deserve further consideration as a cause of the observed differences in molar wear gradient.     

Within-canopy variation in the rate of development of photosynthetic capacity is proportional to integrated quantum flux density in temperate deciduous trees

The present study was undertaken to test for the hypothesis that the rate of development in the capacity for photosynthetic electron transport per unit area (J_max;A), and maximum carboxylase activity of Rubisco (V_cmax;A) is proportional to average integrated daily quantum flux density (Q_int) in a mixed deciduous forest dominated by the shade‐intolerant species Populus tremula L., and the shade‐tolerant species Tilia cordata Mill. We distinguished between the age‐dependent changes in net assimilation rates due to modifications in leaf dry mass per unit area (M_A), foliar nitrogen content per unit dry mass (N_M), and fractional partitioning of foliar nitrogen in the proteins of photosynthetic electron transport (F_B), Rubisco (F_R) and in light‐harvesting chlorophyll‐protein complexes (V_cmax;A ∝ M_AN_MF_R; J_max;A ∝ M_AN_MF_B). In both species, increases in J_max;A and V_cmax;A during leaf development were primarily determined by nitrogen allocation to growing leaves, increases in leaf nitrogen partitioning in photosynthetic machinery, and increases in M_A. Canopy differences in the rate of development of leaf photosynthetic capacity were mainly controlled by the rate of change in M_A. There was only small within‐canopy variation in the initial rate of biomass accumulation per unit Q_int (slope of M_A versus leaf age relationship per unit Q_int), suggesting that canopy differences in the rate of development of J_max;A and V_cmax;A are directly proportional to Q_int. Nevertheless, M_A, nitrogen, J_max;A and V_cmax;A of mature leaves were not proportional to Q_int because of a finite M_A in leaves immediately after bud‐burst (light‐independent component of M_A). M_A, leaf chlorophyll contents and chlorophyll : N ratio of mature leaves were best correlated with the integrated average quantum flux density during leaf development, suggesting that foliar photosynthetic apparatus, once developed, is not affected by day‐to‐day fluctuations in Q_int. However, for the upper canopy leaves of P. tremula and for the entire canopy of T. cordata, there was a continuous decline in N contents per unit dry mass in mature non‐senescent leaves on the order of 15–20% for a change of leaf age from 40 to 120 d, possibly manifesting nitrogen reallocation to bud formation. The decline in N contents led to similar decreases in leaf photosynthetic capacity and foliar chlorophyll contents. These data demonstrate that light‐dependent variation in the rate of developmental changes in M_A determines canopy differences in photosynthetic capacity, whereas foliar photosynthetic apparatus is essentially constant in fully developed leaves.