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Meet a Paleontologist

Josh Bonde Repetski studying an outcrop along the Chesapeake & Ohio Canal National Historical Park, mile post 100 near Williamsport, Maryland.


Josh Bonde Repetski (on the left in red) visiting Charles Walcott's quarry in the Burgess Shale, British Columbia, Canada.

John Repetski

Research Geologist

U.S. Geological Survey

NFD Kid's Page Interview...

What is your job, and what do you study?

My job is to solve problems involving Paleozoic sedimentary rocks (approx. 545 to 250 million years old) using the microfossils called conodonts. Conodont animals lived in most types of marine environments during that long time interval and their teeth, being of the hard mineral apatite, are often preserved and can be extracted fairly easily from many of these rocks. From work over the past 150 years we now know the 'family tree' of conodonts well enough that we can figure out the relative age of conodont-bearing rocks from the species of conodont fossils we find in them, from where they 'fit' into this 'family tree.' We also can tell the approximate maximum temperature these conodont-bearing rocks were subjected to after they were deposited (from heat due to burial or heat from nearby molten rocks or heat from hot fluids moving through the rocks). Each conodont tooth originally had some organic matter with it, and with post-death heating this organic matter changes color, from light yellow to orange to brown to black, and this color change is irreversible. The conodont color gives us a temperature range that the fossil encountered after it died and became part of the seafloor sediment and then the rock record.

What are you working on now?

Currently, I am working with colleagues who are making geologic maps in limestone and dolomite areas in eastern and midwestern U.S. These areas include the Great Valley and Shenandoah Valley in the East and the Ozarks region in the Midwest. These areas have carbonate bedrock, which is prone to sinkoles and is rich in caves because carbonate rocks (limestone and dolostone) are soluble. Mapping the 3-dimensional distribution of the rocks in these regions is important to understand the flow of groundwater (clean and polluted) and to understand and anticipate hazards such as sinkholes. I am also using conodonts to make maps of the thermal maturation levels of potentially oil- and gas-bearing rock units in the eastern U.S. These maps help everyone involved with the issues surrounding oil and gas exploration. For example, the conodonts show areas where the host-rocks have been heated to temperatures too high to expect oil or gas to still be preserved. Likewise they show the areas where the host-rock has been too cool for either oil or gas to have been generated from organic matter in the sedimenary rocks.

Where did you go to school? What were some of your favorite classes that you took?

I grew up near Wheeling, WV, and Pittsburgh, PA, and did my undergraduate studies at Indiana University of Penna. (IUP). Then I did my graduate work at the University of Missouri. In high school, I liked all my courses. Then college was like a smorgasbord, and I tried to sample a lot. I almost majored in music, but decided on earth and space science. In graduate school, most of my courses were in geology of course, and when I decided to concentrate in paleontology I took more higher level biology courses, too.

Was there an experience you had that made you realize you wanted to be a paleontologist?

Growing up, I was always intrigued when I found any fossils, especially because they are not very common in most of the rocks that I lived on (except for coal, of course). In college, one summer I applied for a routine summer job with a driller and the owner showed me this collection of tiny teeth that he picked out of the local limestones by soaking them in strong vinegar. These were the first conodonts that I had seen; in fact I had not heard of them before that. Two years later, when I started graduate school, one of the Univ. of Missouri professors actually specialized in conodonts, and he convinced me that these were not only as interesting as they appeared, but they also were tremendously useful for many different purposes as long as you were willing to do the 'dirty work' in collecting the right rocks and dissolving them and picking out the microfossils under a microscope using a very fine moist brush, then identifying the species from the published literature and reference collections.

What is your most memorable experience working with fossils?

Perhaps my most memorable experience came very early in my professional career. I processed a rock sample from Wyoming that contained some trilobites that showed it to be Late Cambrian in age. I was hoping to find some of the very oldest conodonts, but instead I found a lot of scale-like pieces of ancient fish. Because we had firm evidence of the age of the rock from the trilobites, this meant that these were fragments of the oldest known fish. Publishing the paper moving back the age of the oldest-known fish was pretty exciting, including seeing news clippings from papers from all over the world. Of course, since then older fish fossils have been discovered, and I have been involved in several other discoveries or documentations that are scientifically as or even more significant, but it was certainly one of the most memorable.

Do you have any advice for aspiring paleontologists?

Encourage your curiosity, and don't be afraid to try new things – you might like them. Take as much science and math as you can. Ask questions. You may have the question that others have not thought of, and that might be critical to solving a problem. Read – a lot!

NFD Kid's Page Paleontologist Interviews:

Cassi Knight  Roy Plotnick  Thomas Holtz  Sidney Ash  Joshua Samuels  Alan Titus  Vince Santucci  Josh Bonde 
Michelle Pinsdorf  Glenn W. Storrs  Rebecca Hunt-Foster  Arthur J. Boucot  Robert B. Blodgett  Greg McDonald  Eric Scott  Sally Shelton 
Hans Deitre-Sues  Jim Kirkland  Alton Dooley  Karen Chin  Erica Clites  Katie Loughney  Richard Kissel  Andrew Heckert 
John Repetski  Christy Visaggi  John Hoganson  Scott Foss  Bruce Schumacher  Scott Sampson  Greg Liggett  Jere Lipps 
Matthew Miller  David Brezinski  James Hagadorn  Kari Prassack  Tony Fiorillo  Mike Fracasso  Diana Boudreau  Phil Varela 
Mindy Householder  Andrew Milner 

Cassi Knight
Roy Plotnick
Thomas Holtz
Sidney Ash
Joshua Samuels
Alan Titus
Vincent Santucci
Josh Bonde
Michelle Pinsdorf
Glenn W. Storrs
Rebecca Hunt-Foster
Arthur J. Boucot
Robert B. Blodgett
Greg McDonald
Eric Scott
Sally Shelton
Hans Deitre-Sues
Jim Kirkland
Alton Dooley
Karen Chin
Erica Clites
Katie Loughney
Richard Kissel
Andrew Heckert
John Repetski
Christy Visaggi
John Hoganson
Scott Foss
Bruce Schumacher
Scott Sampson
Greg Liggett
Jere Lipps
Matthew Miller
David Brezinski
James Hagadorn
Kari Prassack
Tony Fiorillo
Mike Fracasso
Diana Boudreau
Phil Varela
Mindy Householder
Andrew Milner


Last updated: June 12, 2013