by Jonathan R. Hendricks
Dr. Hendricks received his B.S. degree from the University of Wisconsin-Madison and his Ph.D. from Cornell University. He is currently an associate professor of geology at San José State University, San José, California.
Although telling people that I study fossils for a living is often a good conversation starter, telling them that my research is focused mostly on snail shells tends to have the opposite effect. Snails can be a tough sell: they are slow, slimy, and many people are perhaps most familiar with them as garden pests. They are, however, a spectacular evolutionary success story. They have mastered marine, freshwater, and terrestrial habitats and along the way have achieved a level of biodiversity trumped only by the insects. Owing to their strong, mineralized shells, snails also have a rich and well-preserved fossil record that extends back hundreds of millions of years. Snails (Phylum Mollusca, Class Gastropoda) are thus a very important group for understanding macroevolutionary processes over geological timescales, including the responses of species to ancient environmental changes.
While many gastropods may not be especially charismatic, that cannot be said of the cone snails (Family Conidae, which includes four genera: Conus, Conasprella, Californiconus, and Profundiconus). Collectors have coveted the beautiful and intricately patterned shells of cone snails for centuries. But that is not what has made them most famous: some cone snails have caused human fatalities! Cone snails—which are found in tropical and sub-tropical marine habitats around the world—are all venomous predators and use a harpoon-like structure to capture and envenomate their prey before it is pulled inside the shell and consumed. These animals are highly specialized predators and usually focus on one type of prey. Most cone snails eat worms, members of one subgroup eat other snails, and two subgroups have even evolved the ability to eat fish. It is the latter species that are especially dangerous to humans, as their venoms have evolved to target vertebrates. Substantial biomedical research is currently being conducted on cone snail venoms for their potential use in developing new drugs. A final claim-to-fame for cone snails is that, with over 700 living species, they are one of the most diverse groups of gastropods.
My paleobiological research is focused on the extensive Eocene to Pleistocene fossil record of cone snails in tropical America, including the Caribbean, Gulf of Mexico, and southeastern United States. In particular, I seek to better understand the origins of the modern cone snail fauna in this region, which—according to a recent taxonomic revision by Dr. Alan Kohn—includes just over 50 species, some of which have fossil records extending back to the Neogene. Paleontologists have extensively researched the Neogene fossil record of tropical America, as it coincides spatially and temporally with the closure of the Central American Seaway (CAS) due to the rise of the Isthmus of Panama. The region thus serves as a “natural laboratory” for understanding how ancient species responded to this significant environmental event, which substantially affected ocean conditions on either side of the Isthmus.
Understanding how the modern fauna developed—including in response to ancient environmental changes like the closure of the CAS—depends upon recognizing ancient species, along with documenting both their durations through time and their biogeographical distributions. While many species of fossil cone snails have been described from tropical America, many of these are synonymous (i.e., multiple names have been assigned to the same species). Recognizing fossil species is often a challenge for taxonomists and this is especially true in groups like cone snails that are diverse, but have relatively conservative shell morphologies. An added problem is that fossil cone shells are often naturally bleached white from the fossilization process, removing evidence of the complex and diverse coloration patterns that are useful for recognizing modern species. In the 1960s, however, Axel Olsson discovered that exposing fossil shells to ultraviolet (UV) light sometimes causes organic matter associated with formerly pigmented regions of the shell to fluoresce, revealing the original coloration patterns of the shells (if not the colors of the pigments themselves). I have found this technique to be very useful for recognizing and differentiating ancient species, as well as for determining their relationships to each other and modern species. A recent article that I published in PLOS ONE on fossil cone shells from the Neogene of the Dominican Republic gives further details on the UV technique, as does a short article I wrote in 2007 for the Florida Paleontological Society. If you decide to try this approach yourself, take proper safety precautions, as UV rays are harmful to both the skin and eyes.
Museum collections—including both fossil and modern specimens—have been and always will be critical to my research program. I have greatly benefited from the efforts of the professional and avocational collectors who originally collected the material that I have studied, as well as the museum staff who curated it and made it available for my research. While direct access to museum collections is typically restricted to staff and visiting scientists, I am interested in ways to make the information contained in such collections more widely available to the general public. Along these lines, I am currently involved with a National Science Foundation supported project—with fellow Principal Investigators Bruce Lieberman (University of Kansas) and Alycia Stigall (Ohio University)—to develop a Digital Atlas of Ancient Life (www.digitalatlasofancientlife.org). This new, freely accessible online resource seeks to assist individuals with the identification of fossil specimens, as well as to provide information about the temporal and spatial distributions of individual species (including maps showing the ranges of ancient species). We are currently focusing on developing Digital Atlases for three regions and time intervals: the Ordovician of the Cincinnati, Ohio region (www.ordovicianatlas.org); the Pennsylvanian of the midcontinent United States (www.pennsylvanianatlas.org); and the Neogene of the southeastern United States (www.neogeneatlas.org). If you are interested in fossils from one or more of these regions, I encourage you to have a look at these websites. You can also follow project updates on Twitter @PaleoDigAtlas.
To learn more:
Read a short article about the UV procedure in the Washington Post.
Dr. Hendricks’ website
Further reading:
Hendricks’ 2015 PLOS ONE paper on fossil cone shells from the Dominican Republic, highlighting coloration patterns revealed on these fossils using ultraviolet light: http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0120924
Hendricks’ 2007 article in the Florida Paleontological Society Newsletter (vol. 24, no. 2) detailing the use of ultraviolet light for revealing ancient shell coloration patterns: http://floridapaleosociety.com/wp-content/uploads/2010/11/fpsfall07.pdf