Laura M. MacLatchy - US grants

Vertical climbing, a behavior frequently performed by extant hominoids and atelines, has figured prominently in theories of locomotor evolution in the hominoids and hominins. For example, it has been proposed that vertical climbing pre-adapted hominins for bipedality. However, whether Pliocene hominins or Miocene hominoids practiced vertical climbing is still a subject of debate. Kinematic work on wild chimpanzees in Kibale National Park, Uganda has shown that vertical climbing requires extreme foot dorsiflexion, coupled with foot inversion and abduction. It is thus hypothesized that the morphology of the ankle, or talocrural joint, in vertical climbing Old World anthropoids is (1) adapted for positions of extreme dorsiflexion, inversion, and abduction, and (2) adapted to withstand the forces incurred on the joint while being loaded in these foot positions. This project will examine the external and internal morphology of the ankle in thirteen species of living primates, including humans, to test whether vertical climbers have a distinct talocrural joint morphology. External morphology of the talocrural joint will be assessed using linear and angular properties of the tibia and talus. Furthermore, the complex shape of the ankle will be modeled using data obtained from 3D laser scans. The role of ankle ligaments in restricting joint motion and stabilizing the ankle will be determined by quantifying the specific location and shape of the bony attachments. Finally, the internal morphology of the talus will be examined using CT scans of modern anthropoid tali. To address whether extinct hominoids and hominins included vertical climbing in their locomotor repertoire, results obtained from the study of modern ankles will be applied to fossil tibia and tali, including CT scan data obtained from seven hominin tali from fossil localities in South Africa.

This project examines the ankle joint across a wide range of modern primates to help reconstruct the locomotion of extinct apes and humans, and test whether early human ancestors were capable tree climbers. This project focuses specifically on the ankle joint to test whether the remarkable tree climbing ability of modern apes has a deep history, and whether vertical tree climbing may have been a precursor to human bipedality. Because the ankle joint is so often injured in modern humans, this study will also track the evolutionary history of ankle ligaments using fossil tibia and tali to determine the timing of and circumstances leading to our modern ankle anatomy.

The goal of this project is to document how chimpanzee locomotion and anatomy develop from infancy through adulthood. Specifically, the extent to which changes in locomotor behavior over time influence changes in skeletal anatomy will be investigated. Infant chimpanzees are typically carried by their mothers when traveling and principally move using their upper limbs. In contrast, juvenile chimpanzees move entirely by themselves, relying more on quadrupedal locomotion. Quadrupedal knuckle walking increases as individuals age. These behavioral transitions are predicted to result in correlated changes in anatomy, with an initial increase in lower limb bone strength and shape as chimpanzees mature from infancy to juvenility. A second change, in knuckle morphology, related to the stress of knuckle-walking, is expected to occur as individuals age and spend more time moving quadrupedally.
This project will integrate observations of chimpanzees in the wild with measurements of bones in museums and analysis conducted in the laboratory. Fieldwork will be conducted in Kibale National Park, Uganda, to document the locomotor behavior of chimpanzees of different ages. Chimpanzees will also be filmed to analyze individual variation in performance within and between locomotor modes. Chimpanzee skeletons from museums will be analyzed using morphological measures, micro CT scanning, and digital photography.
Chimpanzees are our closest living relatives and their behavior likely includes elements shared with our ancestors. A systematic study of how chimpanzee movement affects the shape of bones may enable us to identify morphological features induced by behaviors such as knuckle-walking, bipedalism, and suspension. These features can then be used to reconstruct locomotor behavior in fossil apes and humans and provide a better understanding of how humans evolved into bipedal creatures. Results promise to shed light on problems relevant to several fields of study, including functional morphology, bone growth and development, and human evolution.

New evidence from early fossil humans suggests that, in some respects, these hominins more closely resembled the earliest fossil apes than any modern ape. While such findings substantially impact our understanding of early hominin adaptive morphology, their precise implications remain unclear because the original ecological conditions in which these features evolved is poorly documented. To address this problem, this project will answer the following three research questions: What are the regional patterns of environmental change and the site-specific habitats associated with the earliest fossil apes? How does the morphology of early apes relate to the environmental contexts in which they lived? How do early ape adaptations inform our understanding of later ape and human evolution? These questions will be answered by establishing a multi-disciplinary, multi-national collaboration to initiate new paleontological field research at all of the early fossil ape localities in East Africa. For the first time, new fossil and data collection will be coordinated across nearly a dozen Kenyan sites near Kisingiri, Tinderet, West Turkana, and Buluk, and a similar number of Ugandan sites at Napak, Moroto, and Bukwa. In addition to surveys and excavation, a series of geological, ecological, and taphonomic analyses will be used to understand the age, environment, and setting of each locality. New fossils will be subjected to rigorous morphological analyses to determine their evolutionary and adaptive significance. Unlike previous studies, which have focused on individual localities, this regional approach to understanding ancient ecosystems will track environmental variations over the time and space of early ape evolution, making it possible to relate specific habitat types with primate adaptive morphology.

The origin and early diversification of the ape-human lineage represents a fundamental shift in primate body plans, and is therefore an integral resource for interpreting the later evolution of apes and humans. For decades, most researchers have studied human origins through the lens of modern ape and human characteristics, marginalizing a large and diverse body of evidence from their ancient ape predecessors. This project represents an important and substantive step toward fully integrating our knowledge of living and fossil apes and humans. Moreover, coordinating a project of this breadth - using the same methods and protocols across all of the relevant fossil sites - will allow data to be synthesized on a scale not previously possible, setting new benchmarks for conducting future field projects. This project will thus model a collaborative approach that will be more productive and beneficial to the discipline of paleoanthropology.

This project also generates substantial broader impacts. A critical component of the grant is the training of US and East Africa graduate and US undergraduate students in the discipline of paleoanthropology. The project also includes the National Museums of Kenya as a full collaborative scientific partner in the proposed research. A well-established partnership between University of Michigan, Makerere University and the National Museum (Uganda) will be fostered by this grant, helping to train staff and students in Uganda on field and analytical techniques. Finally, a digital database cataloging all the fossils and data collected from all of the localities will be made freely available after the conclusion of the project.

The goal of this research is to search for new fossil localities in eastern Uganda to understand the evolutionary processes associated with the origin of hominoids, the group of primates that includes apes and humans. The few known fossil sites in this area have yielded ancient animal and plant communities that include fossils of the oldest known apes. One of these apes,"Morotopithecus," shows evidence of using an upright trunk, the earliest known precursor of bipedalism in humans. Fossil data relevant to human origins is rare and evidence of such evolutionary specializations in apes provides critical insights into our evolution in Africa. Eastern Uganda represents one of the few known areas in the world where evidence has been found and further discoveries are essential.

Although the general locations of known fossil sites were established over 50 years ago, there have been no systematic attempts to explore this area for fossil localities. This has been due to the remote nature of this region, rugged terrain, large areas to reconnoiter (over 500 km2), heavy vegetation during all but the two-month dry season, limited geologic maps, and political instability related to armed livestock raiding. A recent national disarmament campaign has led to improved safety as well as the establishment of new settlements and access roads. Using newly available high-resolution satellite imagery, an extensive survey will be conducted (during the critical dry season) for fossiliferous sediments for the first time, possibly resulting in new sites and new fossils.

The broader impacts of this project include fostering of the career of women paleontologists, who are under-represented in field projects, as well as fostering the careers of African scholars in the form of collaborators and students. Researchers will disseminate their science widely through timely publication, teaching, the training of museum staff and public lectures.