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Jocelyn Sessa, assistant professor, Department of Biodiversity, Earth and Evironmental Science, Drexel University

Jocelyn A. Sessa, PhD

Associate Professor
Associate Curator, Invertebrate Paleontology Department, Academy of Natural Sciences of Drexel University
Department of Biodiversity, Earth and Environmental Science
Office: Academy of Natural Sciences of Drexel University
1900 Benjamin Franklin Parkway
Philadelphia, PA 19103
Phone: 215.299.1149

Additional Sites:

Academy of Natural Sciences
Google Scholar


  • PhD, Department of Geosciences, Pennsylvania State University, 2009
  • MS, Department of Geology, University of Cincinnati, 2003
  • BA, Department of Geological Sciences, State University of New York at Geneseo, cum laude, minor in Environmental Studies. 2000

Curriculum Vitae:

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Research Interests:

  • Ocean acidification
  • Mollusks
  • Climate change
  • Paleobiology


Jocelyn A. Sessa, PhD, is a paleobiologist who uses the fossil record as a natural laboratory to study times of change in earth’s history. Her research melds fossil and modern data to elucidate the response of mollusk faunas (clams and snails) to environmental perturbations across space and time. Sessa’s studies span a wide range of events, from the mass extinction that killed off the dinosaurs to past climatic fluctuations, including intervals of past and present global warming. By analyzing the chemistry of mollusk shells, she also reconstructs the climatic conditions that affected ecosystems.

A new research initiative is focused on determining historical baselines for modern ocean acidification, to ascertain whether certain regions or species in the global ocean may be more resilient to future changes in ocean chemistry than others. Sessa’s hunt for mollusks is a worldwide endeavor, with fieldwork along the US eastern seaboard, the US Gulf Coast, California, Romania, and Angola. An important facet of her scholarship is mentoring high school through graduate students in research projects. Sessa is passionate about making science accessible to everyone. Since 2007, she has participated in programs to engage groups under-represented in the sciences and is excited to continue this work in the Philadelphia Area.

Selected Publications:

Note (* indicates student author; for student work, indicates corresponding author):

  • Sessa, J.A., Fraass, A.J., LeVay, L.J., Jamson, K.M.*, Peters, S.E. 2023. The extending Ocean Drilling Pursuits (eODP) Project: Synthesizing Scientific Ocean Drilling Data. Geochemistry, Geophysics, Geosystems: 24
  • Oakes, R.L., Davis, C.V., Sessa, J.A. 2021. Using the stable isotopic composition of Heliconoides inflatus pteropod shells to determine calcification depth in the Cariaco Basin. Frontiers in Marine Science 7:1169
  • Buczek, A.J.*, Hendy, A., Hopkins, M. Sessa, J.A. 2021. On the reconciliation of biostratigraphy and strontium isotope stratigraphy of three southern Californian Plio-Pleistocene formations. Geological Society of America Bulletin 133:100-114
  • Oakes, R.L., Sessa, J.A. 2020. Determining how biotic and abiotic variables affect the shell condition and parameters of Heliconoides inflatus pteropods from a sediment trap in the Cariaco Basin. Biogeosciences 17:1975–1990;
  • Oakes, R.L., Hill Chase, M., Siddall, M.E., Sessa, J.A. 2020. Testing the impact of two key scan parameters on the quality and repeatability of measurements from CT scan data. Palaeontologia Electronica 23(1):a07;
  • Ferguson, K.*, MacLeod, K.G., Landman, N.H., Sessa, J.A. 2019. Evaluating growth and ecology in Baculitid and Scaphitid ammonites using stable isotope sclerochronology. Palaios 34:317-329;
  • O’Leary, M.A., Bouare, M.L., Claeson, K.M., Heilbronn, K., Hill, R.V., McCartney, J., Sessa, J.A., Sissoko, F., Tapanila, L., Wheeler, E., Roberts, E.M. 2019. Stratigraphy and paleobiology of the Upper Cretaceous-Lower Paleogene Trans-Saharan Seaway in Mali. Bulletin of the American Museum of Natural History 436: 177p.
  • Ivany, L.C., Pietsch, C., Handley, J.C., Lockwood, R., Allmon, W.D., Sessa, J.A. 2018. Little lasting impact of the Paleocene-Eocene Thermal Maximum on shallow marine mollusk faunas. Science Advances 4:eaat5528;
  • Jardine, P.E., Harrington, G.J., Sessa, J.A., Dašková, J. 2018. Drivers and constraints on floral latitudinal diversification gradients. Journal of Biogeography 45:1408-1419;
  • Self-Trail, J.M., Robinson, M.M., Bralower, T.J., Sessa, J.A., Hajek, E.A., Kump, L.R., Trampush, S.M.*, Willard, D.A., Edwards, L.E., Powars, D.A., Wandless, G.A. 2017. Coastal marine response to global climate change during the Paleocene Eocene Thermal Maximum,Salisbury Embayment. Paleoceanography 32:1-19;
  • Paynter, A.N.*, Metzger, M.J., Sessa, J.A., Siddall, M.E. 2017. Evidence of horizontal transmission of the cancer-associated Steamer retrotransposon among ecological cohort bivalve species. Diseases of Aquatic Organisms 124:165-168;
  • Janssen, A.W., Sessa, J.A., Thomas, E. 2016. Pteropoda (Mollusca, Gastropoda, Thecosomata) from the Paleocene-Eocene Thermal Maximum of the United States Atlantic Coastal Plain. Palaeontologia Electronica. 19.3.47A: 1-26;
  • Knoll, K.*, Landman, N. H., Cochran, J. K., MacLeod, K. G., Sessa, J.A.2016. Microstructural preservation and the effects of diagenesis on the carbon and oxygen isotope composition of Late Cretaceous aragonitic mollusks from the Gulf Coastal Plain and the Western Interior Seaway. American Journal of Science 316:591–613. The issue cover image is from this article.
  • Sessa, J.A., Larina, E.*, Knoll, K.*, Garb, M. Cochran, J.K., Huber, B.T., MacLeod, K.G., Landman, N.H. 2015. Ammonite habitat revealed via isotopic composition and comparisons with co-occurring benthic and planktonic organisms. Proceedings of the National Academy of Sciences 112:15562-15567;
  • Sluijs, A., van Roij, L.*, Harrington, G.J., Schouten, S., Sessa, J.A., Levay, L.J., Reichart, G.J., Slomp, C.P. 2014. Warming, euxinia and sea level rise during the Paleocene-Eocene Thermal Maximum on the Gulf Coastal Plain: implications for ocean oxygenation and nutrient cycling. Climate of the Past 10:1421-1439.
  • Sessa, J.A., Callapez, P.M., Dinis, P.A., Hendy, A.J.W. 2013. Paleoenvironmental and paleobiogeographical implications of a Middle Pleistocene mollusc assemblage from the marine terraces of Baía das Pipas, Angola. Journal of Paleontology 87:1016-1040.
  • Sessa, J.A., Ivany, L.C., Schlossnagle, T.H.*, Samson, S.D., Schellenberg, S.A. 2012. The fidelity of oxygen and strontium isotope values from shallow shelf settings: Implications for temperature and age reconstructions. Palaeogeography, Palaeoclimatology, Palaeoecology 342-343:27-39.
  • Sessa, J.A., Bralower, T.J., Patzkowsky, M.E., Handley, J.C. Ivany, L.C. 2012. Environmental and biological controls on the diversity and ecology of Late Cretaceous through early Paleogene marine ecosystems in the U.S. Gulf Coastal Plain. Paleobiology 38: 218-239.
  • Sessa, J.A., Patzkowsky, M.E., Bralower, T.J. 2009. Impact of lithification on the diversity, size distribution, and recovery dynamics of marine invertebrate assemblages. Geology 337:115-118.
  • Alroy et al. 2008. Phanerozoic trends in the global diversity of marine invertebrates, Science 321: 97–100.
  • Gibbs, S.J., Bown, P.R., Sessa, J.A., Bralower, T.J., Wilson, P.A. 2006. Nannoplankton origination and extinction across the PETM, Science 314:1770-1773.