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Vertebrate Fauna and Ungulate Biostratigraphy of the Highly Fossiliferous Oso Sand Member, Capistrano Formation, Orange County, CA

Undergraduate #78
Discipline: Ecology Environmental and Earth Sciences
Subcategory: Geosciences and Earth Sciences

Michelle Barboza - California State University, Fullerton
Co-Author(s): By studying fossils are three museums in the Los Angeles area, I was able to compile the first complete faunal list of taxa found in the Oso Sand. From this list, I identified taxa with the potential for diagnostic stratigraphic ranges and gathered samples for further analysis. Based on comparative anatomy, two key taxa were identified to a more specific taxonomic rank, allowing for the study of correlation and overlap of their narrow time range. First, partial camelids (camels) from the Oso Sand can be assigned to the lamine c



The Oso Sand Member is the highly fossiliferous, nearshore facies of the Capistrano Formation, that spans the southeastern rim of the Los Angeles Basin in Orange County, California. Over 20 vertebrate taxa have been identified from this unit, including well-preserved fossils such as a nearly complete skull of a blue marlin and the most complete fossil walrus found to date. In addition to other marine species, terrestrial mammals are also known from the Oso Sand, including gomphotheriids, rhinocerotids, and antelocaprids. Despite the abundance of material produced from Oso Sand Member sites however, just three papers have reported on this unit: one paper focused on the skull of the blue marlin mentioned above, the other two mentioned the assemblage only in passing. Due to lack of study, the age of the Oso Sand remains unclear. Based on stratigraphic correlation, the Capistrano Formation is reported as Upper Miocene to Lower Pliocene, and previous workers have referred to undescribed specimens to place the Oso Sand Member in the Hemphillian North American Land Mammal Age (10.3 – 4.9 Ma). This study provides an overview of all known vertebrate fossils from Oso Sand Member, and uses biostratigraphic analysis to establish a more refined age for the Oso Sand Member.

By studying fossils are three museums in the Los Angeles area, I was able to compile the first complete faunal list of taxa found in the Oso Sand. From this list, I identified taxa with the potential for diagnostic stratigraphic ranges and gathered samples for further analysis. Based on comparative anatomy, two key taxa were identified to a more specific taxonomic rank, allowing for the study of correlation and overlap of their narrow time range. First, partial camelids (camels) from the Oso Sand can be assigned to the lamine camel Alforjas, a genus known from the early to latest Hemphillian (7.0 – 5.3 Ma). Second, equid cheek teeth previously identified as Pliohippus (14 – 6.5 Ma) are reassigned to Dinohippus interpolatus, a taxa characteristic of Hemphillian stage Hh3 (6.7 – 5.9 Ma). Based on these identifications, the age of the Oso Sand Member is constrained from to 6.7 – 5.9 Ma. By better defining the age of the Oso Sand Member, the marine and terrestrial vertebrate fossils from this unit can be placed into a more precise chronostratigraphic framework that allows future research to make more detailed comparisons to other late Neogene faunas in California.

Funder Acknowledgement(s): The authors would like to thank LSAMP (Louis Stokes Alliance for Minority Participation NSF: HRD-0802628), Lisa Babilonia (Ralph B. Clark Regional Park), Bruce MacFadden (Florida Museum of Natural History, University of Florida), Samuel A. McLeod and Jorge Velez-Juarbe (Los Angeles County Natural History Museum), and Meredith Rivin (John D. Cooper Center). This research was funded by the CSU-Louis Stokes Alliance for Minority Participation program (NSF grant # HRD-1302873).

Faculty Advisor: James F. Parham,

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This material is based upon work supported by the National Science Foundation (NSF) under Grant No. DUE-1930047. Any opinions, findings, interpretations, conclusions or recommendations expressed in this material are those of its authors and do not represent the views of the AAAS Board of Directors, the Council of AAAS, AAAS’ membership or the National Science Foundation.

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