Life history of the most complete fossil primate skeleton: exploring growth models for Darwinius

Darwinius is an adapoid primate from the Eocene of Germany, and its only known specimen represents the most complete fossil primate ever found. Its describers hypothesized a close relationship to Anthropoidea, and using a Saimiri model estimated its age at death. This study reconstructs the ancestral permanent dental eruption sequences for basal Euprimates, Haplorhini, Anthropoidea, and stem and crown Strepsirrhini. The results show that the ancestral sequences for the basal euprimate, haplorhine and stem strepsirrhine are identical, and similar to that of Darwinius . However, Darwinius differs from anthropoids by exhibiting early development of the lower third molars relative to the lower third and fourth premolars. The eruption of the lower second premolar marks the point of interruption of the sequence in Darwinius . The anthropoid Saimiri as a model is therefore problematic because it exhibits a delayed eruption of P 2 . Here, an alternative strepsirrhine model based on Eulemur and Varecia is presented. Our proposed model shows an older age at death than previously suggested (1.05–1.14 years), while the range for adult weight is entirely below the range proposed previously. This alternative model is more consistent with hypotheses supporting a stronger relationship between adapoids and strepsirrhines.

Grasping pressures and phalangeal curvature in primates : an experimental in vivo approach

Phalangeal curvature is often used to infer arboreal locomotion in fossil primate species. This is based off an hypothesis of plasticity linked to a loading model that suggests that, when flexed during grasping, a curved phalanx will experience lower internal strains than a straight phalanx. This dissertation is the first in vivo test of this hypothesis. By examining grasping pressures exerted by individual manual and pedal digits during above-branch, below-branch and vertical-branch locomotion, and comparing those pressures to proximal manual and pedal phalangeal curvature, a number of well-accepted but untested hypotheses regarding the relationship between digital form and grasping were tested. 4 adults (2 males, 2 females) each from 4 species of lemur (Lemur catta, Propithecus coquereli, Varecia rubra) were induced to cross an artificial substrate instrumented with a pressure pad at the stated orientations. Digital pressures were then compared to the proximal phalangeal curvature of the same individuals. Findings do not demonstrate any relationship between arboreal grasping at any orientation and digital pressures. This project fails to support previously long-held hypotheses regarding the biological role of phalangeal curvature, and introduces the strong likelihood that a much more complex model of loading is necessary to understand primate phalangeal curvature. Until such a model is devised and tested, using phalangeal curvature to infer arboreal behavior is unsupportable, and should be avoided.