This project will study shape variation in the upper ankle bones of primates of modern aspects (Euprimates) and their closest relatives. Ankle bones are commonly well-preserved in the fossil record, and their shape variation is thought to reflect the way the hind limbs are used in locomotion. The major questions being addressed in this research relate to reconstructing the sequence of changes in locomotion that occurred in the evolutionary origin and subsequent radiation of Euprimates, which will help identify patterns of ancestry through time. The project is novel in utilizing digital imagery, experimental methods, and inclusion of a comprehensive sample of extant and extinct primates. The broader impacts include support of a young investigator, training of graduate and undergraduates of typically under-represented minorities in science. The data will be made available in an online digital library.
The project will focus on generating digital models of primate astragali and calcanei using microCT and laser scanning, and optical topography. Travel is planned to visit museums where obscure and important specimens reside in order to image those specimens. Digital data will be quantified using precise linear measurements, geometric morphometrics, and new automated methods being developed by the PI and collaborators. The data will be analyzed using traditional statistical techniques as well as using new methods that take into account potential non-independence of biological data due to differential phylogenetic relatedness. With this project the PIs will evaluate several types of hypotheses: those concerning the 1) correlation between ankle shape and different modes of locomotion, 2) presence (and significance) of similiarities among certain fossil euprimates (i.e., Adapidae, Omomyidae, Eosimiidae, and definitive stem-Anthropoidea) and the rest of the euprimate radiation, and 3) evolutionary pattern and adaptive significance of shape variation in the primate astragalus and calcaneus.
Summary of outcomes This project provided data leading to improved comprehension of the human condition by executing studies of fossil ankle bones that increased resolution on the ecological transitions of the earliest ancestors of the lineages leading to humans and other living primates. Research was disseminated in the form of 12 peer-reviewed papers and 17 conference presentations so far. In addition, 3D digital models of all specimens observed and measured in this work were made available to other researchers and the general public on a web archive called MorphoSource, created by the PI and hosted by Duke University. This project therefore adheres to federal government mandates for open access publishing of data collected using federal funds. These data are already being used by other researchers, mathematicians, and biostatisticians to address other questions and develop new quantatitive analyses of bones and other biological structures for application to diverse fields of biological inquiry including the clinical realm. It provided support to ten undergraduates, three graduate students, and a female postdoctoral instructor at both Brooklyn College (CUNY), a minority-majority institution, and Duke University. Intellectual Merit Humans are the most successful animal species on earth. Ironically, our greatest strength, an unparalleled ability to expand our niche and thrive, also presents the greatest challenge: We must reign in the exploitation of habitats upon which other species rely, as well as the degradation of the global environment upon which our prosperity relies. Our success as a species can be largely attributed to our ability to observe, interpret, and manipulate our environment. In turn, a suite of distinctive physical traits facilitates this including forward facing eyes and high visual acuity (only raptors have comparable resolving power), a large brain and enhanced cognition, prehensile hands with opposable thumbs, and a capacity for extremely precise (as well as complex and rapid) motor movements as coordinated by visual information. What has made us uniquely "human" in these regards is the long history of environmental changes experienced by our lineage and the corresponding adaptive responses that allowed our ancestors to continue on in new conditions. Our physical traits, the capacities they imbue or restrict, and our behavioral tendencies have been assembled sequentially since the first primates appeared over the last 55 million years. The greatest risks facing humanity and the best strategies for their minimization can only be fully understood by including evidence on this process. To varying degrees, all of the traits mentioned above can be found in other primates suggesting that they have their beginnings in the common ancestor of our group. Clearly, this ancestral species was not using its acute vision to read the newspaper or its fine motor skills to do needle point. In order to understand why these traits originally evolved and what further modifications have been important in the lineage leading to humans, we need to answer the following questions: 1) what were the original environmental and behavioral pressures that led to the evolution key primate features? 2) what was the history of environmental change and adaptive response while primates diversified? The objective of this project was to gather data to help in assessments of these questions. We focused our study on the ankle joints because no other part of the skeleton is as well represented in the fossil record while also being very sensitive to differences in behavior among different species. Thematic and major findings include the following: 1) The first primates differed from their immediate ancestors in exhibiting distinctive improvements in their leaping ability. Our studies highlight a clear imprint of ubiquitous natural selection for leaping and other acrobatic behaviors coinciding with the beginning of primates and during the group’s early diversification. This strongly suggests the visual capacities, brain reorganization, as well as rapid, fine-tuned reflexes and hand-eye coordination were developed and maintained in the context of such behaviors. 2) The beginning of higher primates (monkeys, apes, and humans), is marked by a transition to an environment in which the importance of acrobatic leaping was diminished. If advancements in acrobatic leaping originally served to reduce predation risk by improving the ability for predator evasion (as seems likely based on independent research observing of living lemurs), then early anthropoids must have found other strategies to reduce predation risk. Living in larger groups imbues decreased individual predation risk, but also often leads to greater social complexity and demands for increased cognitive capacity. In sum, this work recruited evidence favoring demands for enhanced acrobatic locomotion as an important selective pressure driving early primate evolution and suggests that relaxation of this pressure corresponds precisely with the beginning of the higher primates. Thus, when anthropoids began to respond to demands for improved function as group-living animals the features they may have co-opted were those formerly maintained by their ancestors for leaping among the branches of shrubs and trees.
