Research: Horse Teeth Reveal the History of the Youngest California Crocs

Editor’s note: Michelle joined the FOSSIL Project in Fall 2016. She comes to us from Southern California, where she produced her undergraduate research and received a minor in Geography / Bachelor of Science in Geology. She is now pursuing a certificate in Women’s Studies and a Masters in Paleontology at the FLMNH/University of Florida with The FOSSIL Project’s founder, Dr. Bruce MacFadden. Other paleo-related experiences include working as a fossil preparator at the John D. Cooper Center in Southern California, and a summer internship with UF’s PCP PIRE program and the Smithsonian Tropical Research Institute in Panama. Michelle is interested in science communication and diversity in STEM; she currently hosts and produces the Femmes of STEM podcast, a bi-monthly show that highlights the stories of women in the history of STEM fields.

by Michelle Barboza

Michelle Barboza holds the tooth of the youngest fossil crocodile known from California, and one of the fossil horse teeth used to determine it's age.
Michelle Barboza holds the tooth of the youngest fossil crocodile known from California, and one of the fossil horse teeth used to determine it’s age.
Infographic © Gabriel Santos
Infographic © Gabriel Santos

Let’s talk about crocs! Florida, home of the FOSSIL project headquarters, is famous for them. “Wait a second,” you might say, “Florida is home of the Gators, not the crocs!” Well, you would be right… if I were referring to crocodiles. However, the subject of this article is not crocodiles, but crocodylians, the order of reptiles which includes alligators, crocodiles, caimans, and gharials.

Now, while the home of The FOSSIL Project is known for its crocs, the home of the newest FOSSIL Project member (me!) is less easily associated with the toothy reptiles. I’m from California, and while crocs aren’t part of our modern landscape, they were certainly a part of our paleontological landscape. In fact, California’s fossil record shows evidence of crocs living in the Golden State in nearly all periods of the Cenozoic era!

This month’s featured research article gives an overview of California croc fossils and, with the help of some horse teeth, shows their presence in the state lasted about 10 million years longer than previously recorded!

So how did this discovery come about? And what does the age of California crocs have to do with horse teeth? Well, while the paper provides an overview of fossil crocs from all over California, it initially started out as a biostratigraphic study and overview of fossils from one location – the Capistrano formation in Southern California. The Capistrano Formation is a shallow marine unit exposed in Orange and San Diego counties. It has produced an extensive fossil fauna, the range of which is housed in five institutions throughout Southern California, including the Natural History Museum of Los Angeles County and the San Diego Natural History Museum. Despite the existence of these collections, the paleontology of the formation is poorly documented in scientific literature.

The nearshore facies of the formation, the Oso Member, is particularly interesting because it has preserved both marine and terrestrial fauna. Biostratigraphy with terrestrial animals allows paleontologists to correlate the member to other fossil sites using North American Land Mammal Ages (NALMA). The dating method of biostratigraphy uses presence of fossils to correlate and assign an age to the strata in which they were found. Fossils useful to biostratigraphy are those of animals that change very rapidly, or existed during limited periods of geologic time, and can thus serve as reliable markers of age. Among the array of specimens found in the Oso Member, including rhinos, gomphotheres, and peccaries, horse teeth were found to be the ideal biostratigraphic markers!

While other animals may have lived during a range of many millions of years, the the type of horse found in the Oso Member of the Capistrano Formation, called Dinohippus interpolatus, was around for less than a million years. That means that the age of the Oso Member is constrained to a narrow period of time from 6.6 – 5.8 million years.

Establishing an age for the Oso Member of the Capistrano Formation put some of the other fossils found there into a new perspective. Crocs for example, were known from California. Previously published records of California crocs included specimens from three counties in Southern California – 60 million year old Paleocene age crocs from the Goler Formation in Kern County (McKenna et al, 1987), 45 million year old Eocene age crocs from six different formations in San Diego County (Golz and Lillegraven, 1977; Busbey, 1986; Brochu, 2013), and 15 million year old Miocene crocs from the Caliente Formation in San Luis Obispo County (Repenning and Vedder, 1961). However, given the newly established age of the Capistrano Formation’s Oso Member, the Oso Member specimens represented the youngest record of crocs ever found!

Michelle examines the size of a fossil horse tooth in the vertebrate paleontology lab at California State University Fullerton
Michelle examines the size of a fossil horse tooth in the vertebrate paleontology lab at California State University Fullerton

Being that many of the myFOSSIL community are avocational paleontologists, I thought I would call attention to these specimens. You can see them for yourself on this infographic created by study author and myFOSSIL member Gabriel Santos, or in the article itself, which is open access. These publication worthy specimens are not beautiful, full skeletons, nor are they skulls. They are simply an individual tooth and single scute (a bony plate). Fossils don’t need to be pretty to be important, they just need to give us good data. The data from these specimens, combined with the data from the horse teeth, let us add a new section to the story of California paleontology!

Learn more about the study:

The age of the Oso Member, Capistrano Formation, and a review of fossil crocodylians from California on Paleobios: http://escholarship.org/uc/item/6sg3v4gs

California State University Fullerton News story: http://news.fullerton.edu/2017wi/crocodile-study.aspx

Paleobios News Story: http://blogs.plos.org/paleocomm/2017/02/08/extending-the-history-of-crocs-in-california/

Infographic: http://paleoparadox.blogspot.com/2017/01/the-age-of-oso-member-capistrano.html

References:

Busbey, A.B. 1986. Pristichampsus cf. P. vorax (Eusuchia; Pristichampsinae) from the Uintan of West Texas. Journal of Vertebrate Paleontology 6:101–103.

Brochu, C.A. 2013. Phylogenetic relationships of Palaeogene ziphodont eusuchians and the status of Pristichampsus Gervais, 1853. Earth and Environmental Science Transactions of the Royal Society of Edinburgh 103:1–30.

Golz, D., and J. Lillegraven. 1977. Summary of known occurrences of terrestrial vertebrates from Eocene strata of Southern California. Contributions to Geology, University of Wyoming 15:43–64.

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