The functional significance of skeletal allometry in Megaladapis in comparison to living prosimians

Slow vertical climbing and clinging are the dominant positional behaviors of the most convincing reconstruction of the primary spatial niche of Megaladapis, a giant extinct prosimian from Madagascar. The vertical support model of Cartmill ('74) predicts that clawless mammals should exhibit relatively elongated forelimbs in expanded size ranges. The allometric corollaries of this model are tested on closely related interspecific samples of Megaladapis and selected extant prosimians. Megaladapis and indriids (vertical leapers and clingers) conform to the structural predictions of the model, and are clearly distinguished from the more pronograde lemurids and cheirogaleids. Extreme hindlimb reduction (negative allometry) is coupled with moderate forelimb elongation (positive allometry) in Megaladapis. These body proportions effectively optimize pedal friction during vertical climbing and minimize the moment of body weight pulling the animal away from the trunk. Positive forelimb allometry occurs in the indriids, while isometry obtains for the hindlimb. The adaptive significance of these morphological strategies are discussed, as are possible selective mechanisms which effect the extreme hindlimb reduction in Megaladapis. Body weight estimates are also presented for Megaladapis edwardsi and Megaladapis grandidieri (50–100 kg and 40–75 kg, respectively).     

Chirotheria and Other Ichnotaxa of the European Triassic

At the end of the Permian, numerous amphibians and therapsids vanished, creating many empty ecological niches, which were occupied by new creatures. This event brought new trends in animal locomotion thanks to modifications of the skeleton limbs. The newcomers were faster and more dangerous for other families. The prominent ichnogenera were Synaptichnium, Chirotherium, Brachychirotherium, Isochirotherium, and Sphingopus. Their trackmakers were Thecodonts, reptiles having the above-mentioned evolutive characteristics. Dinosaurs, which appeared at the end of the Triassic period, were likely their descendants, which raises the question of when and where the dinosaurs originated. The comparison of the trackways of the Middle and upper Triassic with those of the lower Jurassic leads to the conclusion that the two sets of tridactyl ichnites were similar and were made by the same group of trackmakers, the dinosaurs. We had many passionate discussions on this subject with Bill Sarjeant when studying the discoveries made in Europe the past 40 years.     

Effects of size on Vervet (Cercopithecus aethiops) gait parameters: A cross-sectional approach

A comparison of the values of certain temporal and spatial locomotor parameters was made among ten different-aged (sized) vervet monkeys locomoting at nine identical speeds. Cycle and stance durations decreased across speed for all the animals; at any one speed both parameters also varied directly with body size. Stride length increased with speed for all the animals and was greater in the larger animals. Swing duration and hindlimb support length tended to be relatively consistent for each animal across speed, but varied among the animals directly with body size. Hindlimb duty factor decreased with speed for any one animal but showed no direct correlation with size. Hindlimb angular excursion also showed no correlation with size, nor did it show a simple relationship with speed. In terms of gaits and gait transitions, the data indicate that vervets use a very wide variety of gait types, which are not easily correlated with speed or body size. Furthermore, the data suggest the existence of a run–gallop transition zone of speeds for these animals, rather than the existence of a specific transition speed. Finally, the data were used to test intraspecifically the elastic and dynamic similarity models, both of which predict how locomotor parameters will change with size in animals. The results are generally consistent with the dynamic model.     

Long bone scaling in Captorhinidae: do limb bones scale according to elastic similarity in sprawling basal amniotes?

Captorhinids are a speciose clade of sauropsids that are crucial to understand several aspects of basal amniote general biology. Members of the Captorhinidae explored different diets and, amongst basal amniotes, were one of the first groups to demonstrate high‐fibre herbivory. Several papers have been published on the cranial anatomy of captorhinids, but there are relatively few studies which focus on the post‐cranium, especially on the appendicular skeleton and long bones. This contribution presents the first quantitative long bone scaling in Captorhinidae performed through morphometric analyses. From classical biomechanical research, it is well‐established that to accommodate an increase in size, gravity will result in elastic deformation of long bones. This outcome is especially significant in terrestrial tetrapods with a sprawling limb posture such as captorhinids, where great torsional stresses are applied to long bones, both during locomotion and in the resting phase. In this paper, we test whether the consistent evolutionary size increase in captorhinids led to major re‐patterning in long bone structure as theoretically expected, based on the theory of elastic similarity. Morphometric analysis shows that, apart from a small positive allometry in the humerus, captorhinid long bones scale geometrically as body size increases. Thus, the predicted elastic similarity to maintain similar levels in peak stress with an increase in dimensions does not seem not to apply to long bone evolution in captorhinids. We propose that, as already observed experimentally in larger‐bodied varanid lizards, large captorhinids could also mitigate size‐related increases in stress by reducing femur rotation and increasing the percentage of the stride cycle during which the right hindfoot was on the ground (i.e. the duty factor). In this way, large captorhinids could avoid reaching peak stress thresholds by sacrificing speed during locomotion and without a substantial long bone re‐patterning or postural change.     

Problems in discrimination of tridactyl dinosaur footprints,exemplified by the Hettangian trackways,the causses,France

Numerous tridactyl dinosaur footprints have been discovered in the Lower Jurassic (Hettangian) of the Causses, France. They exhibit the usual Grallator‐like morphology in which differences seem to be more a result of normal intraspecific variability than of inherent differences between skeletons. However, such subjective conclusions beg an analytical confirmation, which was the principal objective of this study.

For more reliable shape determinations, typical specimens from well‐preserved footprint ichnofaunas of the Connecticut Valley (USA) were used. Statistical methods are necessary to verify the homogeneity of such footprint populations. Determinations of the variability, confidence interval for the mean, and ratios between length characters are particularly important in reducing the influence of the size of each print. By this method, the ichnospecies Anomoepus intermedius, Eubrontes giganteus, and Grallator sillimani are statistically distinct; the equally distinct new ichnospecies from Saint‐Léons (Aveyron) can be designated as Grallator lescurei and the trackways of Saint‐Laurent as G. minusculus.

A problem remains in classifying the trackmaking dinosaurs. Their prior assignment to the theropods apparently should be revised because of the abundance of grallatorid footprints in the Lower Jurassic, which seems to contradict conclusions drawn from paleoecological data.     

Deep evolutionary diversification of semicircular canals in archosaurs

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Paleobiology of Etruscan populations

A research project on the population biology of ancient Etruscans has recently started. The aim of this multidisciplinary research is the anthropological definition of Etruscan populations, about which little is known. The study of the skeletal remains is expected to lead to the identification of characteristics typical of this group, which will be used to establish affinities and differences with other contemporary Italic populations, as well as with previous and subsequent groups. An outline of the project is presented here, together with an indication of the problems concerning the availability of material. A summary of previous research on Etruscans is also given. In the final section, preliminary results are presented on one aspect of the research presently under way, namely the odontometric study of different groups of Etruscan populations. These results suggest a homogeneity within the groups described under the common label “Etruscans”.     

Allometric equations for predicting body mass of dinosaurs

We use data from the literature to compare two statistical procedures for estimating mass (or size) of quadrupedal dinosaurs and other extraordinarily large animals in extinct lineages. Both methods entail extrapolation from allometric equations fitted to data for a reference group of contemporary animals having a body form similar to that of the dinosaurs. The first method is the familiar one of fitting a straight line to logarithmic transformations, followed by back-transformation of the resulting equation to a two-parameter power function in the arithmetic scale. The second procedure entails fitting a two-parameter power function directly to arithmetic data for the extant forms by nonlinear regression. In the example presented here, the summed circumferences for humerus plus femur for 33 species of quadrupedal mammals was the predictor variable in the reference sample and body mass was the response variable. The allometric equation obtained by back-transformation from logarithms was not a good fit to the largest species in the reference sample and presumably led to grossly inaccurate estimates for body mass of several large dinosaurs. In contrast, the allometric equation obtained by nonlinear regression described data in the reference sample quite well, and it presumably resulted in better estimates for body mass of the dinosaurs. The problem with the traditional analysis can be traced to change in the relationship between predictor and response variables attending transformation, thereby causing measurements for large animals not to be weighted appropriately in fitting models by least squares regression. Extrapolations from statistical models obtained by back-transformation from lines fitted to logarithms are unlikely to yield reliable predictions for body size in extinct animals. Numerous reports on the biology of dinosaurs, including recent studies of growth, may need to be reconsidered in light of our findings.     

The ontogeny of sexual dimorphism in the facial skeleton of the African apes

This paper aims to test the contribution of ontogenetic scaling to sexual dimorphism of the facial skeleton in the African apes. Specifically, it addresses whether males and females of each species share a common postnatal ontogenetic shape trajectory for the facial skeleton. Where trajectories are found to differ, it is tested whether male and female trajectories: 1) diverge early, or 2) diverge later after sharing a common trajectory earlier in the postnatal period. Where ontogenetic shape trajectories are found to be shared, it is also tested whether males and females are ontogenetically scaled. This study uses geometric morphometric analyses of 28 landmarks from the facial skeletons of 137 G. g. gorilla (62 adults; 75 juveniles), 95 P. paniscus (34 adults; 61 juveniles), and 115 P. t. troglodytes (58 adults; 57 juveniles). On average, males and females share a common ontogenetic shape trajectory until around the eruption of the second permanent molars. In addition, for the same period, males and females in each species share a common ontogenetic scaling trajectory. After this period, males and females diverge both from each other and from the common juvenile ontogenetic shape and scaling trajectories within each species. Thus, the male and female facial skeleton shows ontogenetic scaling until around the point of the eruption of the second molar (i.e., around puberty and the development of secondary sexual characteristics), but subsequent sexual dimorphism occurs via divergent trajectories and not via ontogenetic scaling.