Evolutionary relationships among fossil plesiadapiforms (putative early primates) and other closely related mammals (primates, treeshrews, and flying lemurs) have been debated for decades. Several recent analyses suggest that plesiadapiforms are most closely related to primates of modern aspect, and are therefore critical for testing hypotheses regarding the origin and earliest evolutionary history of primates. The aim of this project is to clarify which anatomical features separate primates from other mammals, and to elucidate the order in which certain modern primate features evolved following the divergence from non-primate mammals. This project will analyze the paleobiology and systematics of the Micromomyidae; the most primitive family of plesiadapiforms for which postcrania are known. Functional analyses of all known micromomyid fossil material, including four undescribed skeletons, will be interpreted in the context of a new phylogenetic tree. Modern methods in phylogenetic systematics will be utilized, including combined morphological and molecular analyses, and Bayesian methods for morphological data. Although these techniques are gaining popularity in other areas of evolutionary biology, they have not yet been used to assess relationships among primates and their close relatives. Innovative methods integrating micro CT scans will be used to quantitatively compare micromomyid skeletons to those of closely related mammals, and to reconstruct the diversity of positional behaviors and grasping abilities of the most primitive primates. Micro CT scans will also be used to quantify tooth crown dimensions, and determine the dietary habits of primitive primates.
This research will promote a better understanding of the first clear step in the divergence of humans from other mammals. Undergraduate students will be trained in all areas of data collection, and all data will be uploaded to online digital archives. Outreach includes the proposal of an exhibit on primate origins at the Yale Peabody Museum, as well as lectures at local high schools.
This research project aimed to improve our understanding of primate origins and the earliest evolutionary history of Primates, the order to which humans belong. The family Micromomyidae is the most primitive family of plesiadapiforms (putative early primates) for which partial skeletons are known. Results from this project suggest that Micromomyidae is currently represented by five genera and eleven species, and analysis of almost all known fossil specimens of micromomyids has led to a hypothesis of interrelationships for the family. Partial skeletons of Paleocene and Eocene (56-55 Ma) micromomyids were prepared out of freshwater limestone nodules, and new skeletal elements were discovered based on clearly documented associations of bones. These skeletons suggest that micromomyids were tree-dwelling animals, and these fairly complete and associated skeletons were used to search for isolated skeletal elements of older plesiadapiforms in museum collections. Such comparisons ultimately led to the discovery of ankle bones of the oldest (65 Ma) and most primitive primate, Purgatorius, which indicate that this early primate also lived in the trees. These new data, and additional data collected from skeletons of other plesiadapiforms and euarchontan mammals (primates, treeshrews, and colugos) were incorporated into three different phylogenetic analyses to better understand evolutionary relationships among euarchontan mammals. All three analyses supported plesiadapiforms as more closely related to primates than to treeshrews or colugos. In addition to these results, this project also produced a large collection of digital data generated by scanning bones and fossils of primates and their closest relatives with high-resolution CT scanning technology. These digital data will be used in several future studies of plesiadapiform relationships and functional anatomy. This research project provides an understanding of the first clear step in the divergence of our order from other mammals. Undergraduate and graduate students were trained in comparative anatomy, digital photography, and three-dimensional visualization software for analyzing CT scans. Data will be uploaded to public digital archives following publication of the results. Outreach includes the proposal of an exhibit on primate origins at the Yale Peabody Museum, where preliminary results of this project have already been presented orally to the public. Results have also been presented at two universities, and a course partially based on this project, "After the Dinosaurs: The Earliest Primate Radiations," has been designed for an undergraduate class and is currently being taught at Brooklyn College, City University of New York.
