By James F. Parham, John D. Cooper Archaeological and Paleontological Center, Department of Geological Sciences, California State University, Fullerton, CA
The student-led research in my lab at Cal State Fullerton is largely based on a wealth of unstudied, fossils recovered from development mitigation projects around Orange County, California over the past 30 years. This important resource (the Orange County Paleontology Collection) is managed by collaboration between Orange County Parks and Cal State Fullerton called the John D. Cooper Archaeology and Paleontology Center (“Cooper Center”). The Cooper Center fossils range in age from the Jurassic to the Pleistocene, although the majority of the specimens are from the Miocene (~23-5 Ma) and especially from three marine formations that span ~16.5-6 Ma (The Topanga [~16.5-14.5], Monterey [~15-7.], and Capistrano Formations [~7-6]). My student collaborators and I are busy curating, describing, and interpreting the fossils from this time period and we are particularly interested in comparing how assemblages of marine vertebrates change through time.
There are many aspects of the fossil record of Orange County that make it an attractive area for comparative study. For one, Orange County is rich in fossils. The sheer amount of fossil material provides ample opportunities for research projects on a variety of species. We have active projects on sharks, turtles, walruses, seals, sea lions, desmostylians, crocs, and seabirds. Second, the rich fossil record of Orange County is in a small geographic area, so we do not have to consider latitudinal differences when we compare sites. Third, the main time period of interest (~16.5-6 Ma) represents a period of great change in the Eastern Pacific, and around the world, with global temperatures dropping from the Middle Miocene Climatic Optimum to the glacial-interglacial cycles we exist in today. In California we also see the development of enhanced nutrient upwelling systems, and in Orange County we have generally shallowing upward sequence of marine rock units. The overarching theme of our research is to interpret the unstudied marine vertebrate record of Orange County in light of these related physical drivers (climate, currents, and sea level).
Earlier this year, two studies from our lab were published. The first study was “A specimen-based approach to reconstructing the late Neogene seabird communities of California” (Kloess and Parham 2017). Peter Kloess, a graduate student in my lab (now in PhD program at UC Berkeley), examined over 500 seabird fossils from around California, almost half of which were from Orange County. We used this dataset to look at the diversity and abundance of fossil seabirds through the Miocene to test patterns that were originally based on surveying the literature. Among other things, our specimen-based approach demonstrated that a group of flightless auks (mancallines) showed a major increase in abundance during the latest Miocene. This striking pattern is certainly influenced by the preservation potential of their relatively thick bones combined with more nearshore environments preserved in late Miocene rocks, but we also note that it coincides with stable nutrient upwelling that have also been invoked as drivers of fish morphology and pinniped speciation. Our study on seabirds is the most rigorous and quantitative analysis of marine vertebrate community changes in the East Pacific and sets the stage for future studies of faunal change in the Neogene of coastal California.
In order to compare fossils from different sites and formations it is crucial to have accurate and precise ages. That is why, along with documenting the species from Orange County, we are also looking at refining the age of different rock units. The second study we published this year addresses that issue for the Oso Member of the Capistrano Formation, a nearshore fossiliferous rock unit that includes both terrestrial and marine vertebrate fossils. Although many specimens have been recovered from the Oso Member only one study on vertebrate fossils had been published. Michelle Barboza, an undergraduate student in my lab (now in MSc program at the University of Florida), led a biostratigraphic analysis of fossil horse teeth that allowed us to refine The Oso Member’s estimated age from 7.7-5.3 Ma to 6.6-5.8 Ma. Working together with other students and Dr. Velez-Juarbe of the Natural History Museum of Los Angeles County, we provide the first faunal list of the Oso Member. We also note that the Oso Member includes the youngest crocodylians from the western USA. As we prepared our study we found that the fossil record of crocodylians in California was underreported in the literature and so we reviewed and figured specimens from throughout the state.
These two studies are important chapters of the story about how assemblages of marine vertebrates change through time in California. Similar studies are planned over the next few years along with standalone studies on that reveal new data about the paleobiology of extinct species or describe new taxa and evolutionary trees. Aside from the two studies highlighted here, there are other recent studies on the vertebrate paleontology of Orange County, including Cooper Center fossils, that show it’s emerging potential for significant scientific contributions (Boessenecker and Churchill 2015, Santos et al. 2016, Velez-Juarbe 2017).
Works Cited
Barboza, M.M., J.F. Parham, G.-P. Santos, B.N. Kussman, J. Velez-Juarbe. 2017. The age of the Oso Member, Capistrano Formation, and a review of fossil crocodylians from California. PaleoBios 34:1-16. http://escholarship.org/uc/item/6sg3v4gs
Boessenecker, R.W., M. Churchill 2015. The oldest known fur seal. Biology Letters 11(2):20140835. http://rsbl.royalsocietypublishing.org/content/11/2/20140835
Kloess, P.A., and J.F. Parham. 2017. A specimen-based approach to reconstructing the late Neogene seabird communities of California. Palaeogeography, Palaeoclimatology, Palaeoecology 468:473-484. http://www.sciencedirect.com/science/article/pii/S0031018216309282
Santos, G.-P., J.F. Parham, and B.L. Beatty. 2016. New data on the ontogeny and senescence of Desmostylus. Journal of Vertebrate Paleontology 36(2):e1078344. http://www.bioone.org/doi/abs/10.1080/02724634.2016.1078344
Velez-Juarbe, J. 2017. Eotaria citrica, sp. nov., a new stem otariid from the “Topanga” Formation of Southern California. PeerJ 5:e3022. https://doi.org/10.7717/peerj.3022