Cercopithecoid Evolutionary History and Its Relationship to Hominin Biochronology
This is an ongoing Wenner-Gren funded project (along with colleagues S. Frost- Univ. of Oregon and E. Delson- CUNY) aimed at revising the biochronological dates of Plio-Pleistocene hominin sites in Africa using cercopithecoid monkeys as indicator taxa. Despite recent advances in chronometric techniques, considerable uncertainty remains regarding the age of many Plio-Pleistocene hominin sites, particularly those in South Africa. Consequently, biochronology and relative dating methods remain important in assessments of Plio-Pleistocene geochronology. Cercopithecoid monkeys have been among the most useful taxa for biochronology because they are widely present and abundant members of the African Plio-Pleistocene fossil record.
Over the last few years, we have visited every major collection of cercopithecoids derived from African Plio-Pleistocene hominin sites, revising the taxonomy and faunal lists at each site, and we have thus begun to correlate absolute dates across East and South Africa using shared faunal elements (e.g., Gilbert et al., 2016). We are currently in the writing stage of this project, and we also have a contract to complete an edited book (C. Gilbert and S. Frost) detailing the results of our project in full. We plan to complete this book in 2022, and we have included numerous students as collaborators and co-authors on various papers/chapters associated with this project. Our recent publication revising the taxonomy of the genus Papio (baboons) can be found here.
Primate Evolution in the Indian Lower Siwaliks
Fossil apes have been known from Lower Siwalik deposits surrounding Ramnagar since Barnum Brown’s AMNH expedition, 1921-1923. Paleontological fieldwork has continued sporadically at Ramnagar ever since, and in that time, a relatively small number of additional ape specimens and a single adapoid primate have been recovered. In 2010, we began paleontological fieldwork in the Ramnagar region with a focus on studying South Asian primate/mammalian evolution and biogeography. Our team (C. Gilbert- CUNY, B. Patel- USC, R. Patnaik- Panjab Univ., and C. Campisano- Arizona State Univ.) has documented a number of new fossiliferous localities and recovered new primate specimens representing the first new primate taxa recognized at Ramnagar in almost 40 years (a sivaladapid and the earliest known gibbon). Thus, our recent finds have doubled the known taxonomic diversity of primates at Ramnagar and suggest a unique primate fauna not documented elsewhere in the Lower Siwaliks. We are continuing paleontological and geological work at Ramnagar (funded by the Leakey Foundation and National Science Foundation) in 2022 and beyond in an attempt to find additional rare primates, find biochronologically informative micromammals, revise the stratigraphy, and collect paleomag samples. Graduate and undergraduate students have been co-authors on many of our Ramnagar publications thus far and continue to work with us on the project, including two Leakey Baldwin Fellows (Deepak Choudhary and Wasim Wazir).
Nyanzapithecus alesi and its implications for hominoid evolution
I was recently involved in describing the most complete Miocene ape cranium yet known in the African fossil record and detailing its significance for understanding hominoid evolution (Nengo et al., 2017); I continue working with an active research group assessing this specimen and its implications for hominoid evolution. We recently held a workshop in March 2018 (funded by the Leakey Foundation) to plan out future steps in the research of this amazing specimen, and my former graduate student (now colleague), Dr. Kelsey Pugh, is involved in this project as well. Working on this specimen and Miocene apes more broadly, we hope to conduct a broad phylogenetic analysis of catarrhine and ape taxa that builds and improves upon previous analyses by including craniodental + postcranial characters and employing more modern techniques that have been demonstrated to generally improve phylogenetic accuracy. In summary, this project offers the opportunity to help clarify Miocene hominoid phylogenetic relationships and offer updated and (hopefully) more accurate hypotheses regarding hominoid evolution.
Early Eocene Primate Evolution: Paleoenvironmental and Paleoecological Responses to Climate Change
Along with my colleagues Stephen Chester (Brooklyn College, CUNY), Ross Secord (Univ. of Nebraska, Lincoln), and Amy Chew (Brown Univ.), I am also involved in a paleontological project aimed at understanding the paleoenvironment and paleoecology during the Early-Middle Eocene of Wyoming, the warmest period of the last ~56 million years, and its relation to primate and mammalian diversity during this time. Since 2015, we have conducted exploratory expeditions in the Wind River Basin (WRB), WY, one of the best-documented sequences covering the Early-Middle Eocene in North America, and we collected and deposited new fossil material at the American Museum of Natural History (AMNH) as a direct result of our efforts. We have been able to include undergraduate and graduate students in this fieldwork, and it is an outstanding opportunity for affiliated students to gain experience finding early primate and mammalian fossils.
Taxonomy and Evolutionary Morphology of the Guenons (Tribe Cercopithecini)
In addition to analyses of fossil primates, I also maintain an active research program investigating the anatomy and adaptations of new and extremely rare extant monkeys, such as the recently described C. lomamiensis from the TL2 research area of the Congo’s Central Basin (with Eric Sargis- Yale Univ.; Kate Detwiler- Florida Atlantic Univ., John and Terese Hart- Lukuru Wildlife Research Foundation). Along with my graduate student Ms. Julia Arenson, we recently described the skeletal anatomy of C. lomamiensis in the broader context of guenon evolution (funded by a Professional development grant from AAPA, as well as internal grants from Hunter College and CUNY), with our results demonstrating that, despite being thought of as an arboreal radiation, guenons have adapted terrestrial behaviors numerous times during the course of their evolutionary history. Furthermore, we have also recently described new skeletal material of the little-known dryad monkey (Chlorocebus dryas) from the TL2 forest that help to resolve the long-contested taxonomy of C. dryas, with results strongly indicating that C. dryas and C. salongo are indeed the same species. We continue to work on more detailed anatomical studies of these new specimens combined with genetic work as well. Finally, we have collected data on skulls and skeletons of nearly all known guenon taxa and are ultimately working towards a large “total-evidence” phylogenetic analysis aimed at clarifying the still unresolved phylogenetic relationships among the group.
Lateral views of the fossil monkey Procercocebus antiquus (left column) from Taung compared with extant Cercocebus specimens (right column). Male specimens in the top row, female specimens in the bottom row.
From Gilbert (2007). PHOTO CREDIT: Chris Gilbert
Searching for fossils at the site of Sunetar near Ramnagar, India.
PHOTO CREDIT: Biren Patel
Cranium of Nyanzapithecus alesi shortly after excavation at Napudet, Kenya.
PHOTO CREDIT: Isaiah Nengo
Fieldwork in the Wind River Basin, Wyoming.
PHOTO CREDIT: Ryan Schaars
Newly discovered African guenon from the TL2 region of the Congo, Cercopithecus lomamiensis (the lesula).
DRAWING: Kim Honda