Wooster’s Fossil of the Week: A trilobite hypostome (Upper Ordovician of southern Ohio)

August 21st, 2011

We had a familiar trilobite last week, so this week we’ll look at a poorly-known part of a trilobite: the hypostome. Above is an incomplete forked, conterminant hypostome of the large trilobite Isotelus. (Isotelus, by the way, is the state fossil of Ohio. Do you know your state fossil?)

Hypostome means “under mouth”. On trilobites it is found underneath the cephalon (head) near what we think was the mouth. They are not common in the fossil record. It is obvious from their color and composition that they are part of a trilobite, but most people don’t know about this little plate on the otherwise soft underside (the ventral side) of the animal. The hypostome is important in some new taxonomic schemes for sorting out the trilobites (Fortey, 1990), and they are useful for interpreting a particular trilobite’s feeding habits (Fortey and Owens, 1999).
Trilobite hypostome forms from Wikipedia (via Obsidian Soul). The small green plates are the hypostomes seen against the gray cephalon above. A – Natant: Hypostome not attached to doublure; aligned with front edge of glabella (shown in red broken lines). B – Conterminant: Hypostome attached to rostral plate of doublure. Aligned with front edge of glabella. C – Impendent: Hypostome attached to rostral plate but not aligned with glabella.

The hypostome of Isotelus is attached to the anterior edge of the skeleton (thus “conterminant”) and has two distally-directed prongs (making it “forked”). Hegna (2010) has recently suggested this hypostome with its unusual shape and terraced outer structure may have been used for grinding food rather than serrating it. Turns out our hypostome has a unique form among the common trilobites!


Fortey, R.A. 1990. Ontogeny, hypostome attachment and trilobite classification. Journal of Paleontology 33: 529-576.

Fortey, R.A. and Owens, R.M. 1999. Feeding habits in trilobites. Palaeontology 42: 429–65.

Hegna, T.A. 2010. The function of forks: Isotelus-type hypostomes and trilobite feeding. Lethaia 43: 411-419.

Wooster’s Fossil of the Week: A chain coral (Silurian of Ohio)

June 19th, 2011

For some reason the Fossil of the Week I’ve had the most comments about is the Ordovician honeycomb coral from Indiana. It has an unexpected polygonal symmetry reflected in many other geological materials like desiccation cracks and columnar basalt. So this week’s fossil is another coral with a surprising shape: the chain coral Halysites.

Halysites is a tabulate coral genus originally named by Johann Fischer von Waldheim in 1828. Its corallum (colonial skeleton) consists of long vertical tubes (corallites) laterally attached to each other in ranks so that a cross-section looks like a series of chain links. Each corallite held a single coral polyp (an individual) that collected zooplankton for food. The spaces between the ranks — the empty holes — are called lacunae.

A closer view of the halysitid corallum. This specimen is replaced with silica so the surrounding limestone matrix could be removed by dissolving it in hydrochloric acid.

Halysites lived only in the Ordovician and Silurian (about 480 to 420 million years ago), so it is a rough index fossil for these periods. They were especially common in coral reefs, adding stability because their lacunae filled with sediment making them very difficult to dislodge by currents.

Thin-section of a halysitid coral with limestone matrix still in the star-shaped lacunae.


Motus, M.-A. and Klaamann, E. 1999. The halysitid coral genera Halysites and Cystihalysites from Gotland, Sweden. GFF 121: 81-90.

Wooster Tree Ring Lab Ready for Business

June 10th, 2011

Guest blogger Jon Theisen

Beginning May 17th and running until June 10th, the College of Wooster Tree Ring Lab has been partnering with and funded by The Center for Entrepreneurship in an effort to demonstrate the viability of dendrochronological dating as a business opportunity.   The professor in charge of the Tree Ring Lab, Greg Wiles, and his employees, Jon Theisen and Anna Mudd, have spent the last four weeks collecting and dating samples gathered from the towns of Worthington and Somerset, Ohio.  The first week of the project consisted of traveling to the towns of Worthington and Somerset, which are approximately two hours south of Wooster.

Greg Wiles and Jon Theisen consulting with Somerset Mayor Tom Johnson in the Ridenour Barn, one of the many structures sampled by the Wooster Tree Ring Lab

On Tuesday, May 17th, members of the Tree Ring Lab traveled to Worthington, Ohio, in order to sample two structures for the Worthington Historical Society.  The first structure was the Old Rectory, which the Tree Ring Lab successfully dated to 1846.  The Old Rectory was built to house the reverends of St. John’s Episcopal Church.

In the afternoon, members of the Tree Ring Lab went to the Orange Johnson House, just a quick drive from the Old Rectory, in order to gather tree ring samples.  The Orange Johnson House was successfully dated to 1811 for the original structure.

The next day, researchers traveled to Somerset, Ohio, to meet with the Mayor, Tom Johnson.  Mayor Johnson had a number of structures that he wanted dated, so the Tree Ring Lab got to work.

The front of the Miller Tavern in Somerset, Ohio.  Although the exterior of the building has been renovated, the interior beams of the building are still original.

The first building the team sampled in Somerset, Ohio, was the Miller Tavern.  The image above is of team member Jon Theisen using a hand auger to retrieve a wooden core sample from a wall beam in Miller Tavern.  The Miller Tavern was successfully calender dated to 1808.

The team spent Thursday, May 19th in the Tree Ring Lab becoming familiar with the equipment and computer programs they would use to date the cores retrieved from the structures we sampled.  Below is an image of what the retrieved cores look like after they have been sanded and mounted.

The retrieved cores are glued into wooden mounts, and then sanded with a belt sander and high grit sandpaper until they are very smooth and the individual rings can be seen under the microscope.  The cores are counted and the total number of years represented by individual rings is written on the side of the mount.  After the initial count is completed, the cores are placed on the Acu-Rite measuring system, and by using a computer program called Measure J2X, the width of the individual tree rings is measured to the nearest 0.001mm.  These measurements are saved to a computer file where they can then be edited.  A computer program called COFECHA is then used to compare the ring width data of cores taken from a single structure against each other to create a “floating” chronology where the cores are relatively dated against one another.

An example of how cores can be dated relative to each other in order to develop a “floating” chronology

Once a “floating” chronology has been developed for a structure, the ring width measurements are compared against a calendar dated master series of measurements that have been previously dated.  By comparing the “floating” chronology against the master series, a calendar date can be assigned to the structure.

After a day in the lab, the team was ready to get back out in the field and continue gathering samples.  Friday, May 20th saw members of the Tree Ring Lab return to Somerset, Ohio, to gather samples from more structures off of Mayor Tom Johnson’s list.  In the morning the team stopped at the Linnabary House, pictured below, to take a sample.  According to the owners, the house was originally used as a church.  The beam was successfully dated to 1823.

In the afternoon, the team collected samples from two structures.  The first building was the historic library of Somerset, which was still in use today.  The team went down to the basement of the library, pictured below, and gathered samples from the joists supporting the floor.  The library was successfully dated to 1818.

After the library, the team traveled into the country and visited the Johnson House, pictured below.  While the building had been damaged by recent storms that downed trees, Tom Johnson is hoping that a date for when the structure was built will help secure funds for rehabilitating the structure.  The Johnson House was calendar dated to 1817.


After the first week in the field, the team spent the following three weeks in the Tree Ring Lab sanding, counting, and dating cores.  During this time, Jon Theisen and Anna Mudd created seven reports detailing the findings for each structure, a poster, and a blog post.  The reports consist of the name of the structure, a description of the dating techniques used, the calendar date of the samples, and a graph showing how well the measured samples correlate with the master series they were dated against.

These four weeks have shown members of the Tree Ring Lab that there is a great demand for dendrochronological dating.  Dr. Wiles has continued to receive requests for the Tree Ring Lab to visit sites across Ohio in order to gather samples and provide dates for historic structures.

A muddy but successful encounter with the Mississippian-Pennsylvanian boundary in southern Ohio

April 30th, 2011

Lindsey and Richa work their way up the Pennsylvanian section with their Jacob's staffs.

JACKSON, OHIO — Usually the Sedimentology & Stratigraphy class from Wooster meets no one at this Carboniferous outcrop on US 35 in Jackson County. This morning, though, we arrived to find geology students from Wright State University (under Professor David Dominic) hard at work on the section, and the clubhouse for the Apple City Motorcycle Club had a busy (and noisy) crowd as well. We waded right in and started measuring and describing the rocks.

The recent rains had their predictable effect on the shale units, producing a thick mud in some places, but we did well enough staying on the sandstones and conglomerates when we could. I noted that the outcrop is much more overgrown than when I first visited with a Sed/Strat class in 2000. (The better exposures made for better photography of the rock units, as you will see.) Here is another set of images from the 2009 field trip to this site.

This is one of the best places in the state to see the unconformity between the Mississippian and Pennsylvanian subsystems. It is a sharp disconformity above the Logan Formation siltstones and below pebble-rich sandstones of the Sharon Conglomerate equivalent. We drew measured stratigraphic columns through this interval and then met as a group on the top of the outcrop to assess the ancient depositional environments.

We all returned home safely with muddy boots and new ideas about the local stratigraphy.

Joe and Will confer on an outcrop of black, carbon-rich shale.

If it’s spring in Ohio, it’s time for fieldwork!

April 28th, 2011

WOOSTER, OHIO–My geology colleagues have already been braving the weather to get their students into the field after the long winter. I like to wait until the end of April when it’s all sunshine and flowers. This week the Sedimentology & Stratigraphy class started its fieldwork with a visit to the Logan Formation exposed in an overgrown quarry an easy walk from campus. The Tuesday section experienced a bit of rain near the end of their work, but today’s section had a glorious day (much like last year at this time and place). In the image above we see Whitney, Jenn and Melissa describing and measuring the sandstones and conglomerates of the Logan with their fancy Jacob Staffs.

Kevin, Anna and Genevieve arrayed on the outcrop.

Oscar and Marytha conferring on the composition of the granules in the conglomerate.

The conglomerate in the midst of the very fine sandstones of the Logan Formation is the most distinctive unit.

The conglomerate has a sharp lower base and shows graded bedding.

Our little afternoon field trip is practice for this weekend’s class expedition to the Mississippian-Pennsylvanian boundary sections in Jackson County, southern Ohio. Hope we have the same kind of weather!

Wooster’s Fossil of the Week: A woolly mammoth tooth (Late Pleistocene of Holmes County, Ohio)

March 27th, 2011

Since we had a mastodon tooth as our last Fossil of the Week, paleontological symmetry demands we have a mammoth tooth this week. The fossil above also comes from the productive bogs of Holmes County a few miles south of Wooster.

Our tooth is from a young woolly mammoth (Mammuthus primigenius). These were true elephants, unlike the mastodons which were only distant cousins in another family. You can tell a mammoth tooth from a mastodon tooth by the flat ridges on its chewing surface rather than pointy cusps.

The woolly mammoth had long tusks (one of which we have in a display case outside my office) and, of course, plenty of long hair to keep it warm in the tundra environments it inhabited. They were grazers, apparently digging up grass and other ground vegetation with their tusks.

Mammuthus primigenius appeared about 150,000 years ago during the Pleistocene, and the last individual died surprisingly only 3700 years ago on a small Alaskan island. They are well known from frozen remains in Siberia — and from a new Japanese attempt to clone them from frozen tissue. (I’ve heard that one so many times …)

In June 2008, a Wooster Independent Study team saw cross-sections of mammoth footprints at The Mammoth Site, Hot Springs, South Dakota (see below). They could only be identified as such because of the dozens of mammoth skeletons around them!

Woolly mammoths in northern Spain (from a mural by Mauricio Antón).

Wooster’s Fossil of the Week: A mastodon tooth (Late Pleistocene of Holmes County, Ohio)

March 20th, 2011

Time for a vertebrate fossil from the College of Wooster paleontology collections.  Above is a side view of an American Mastodon tooth (Mammut americanum) from the Pleistocene of the county just south of us. It has been passed around through hundreds of student hands in our geology classes to demonstrate basic features of these large animals and their dietary habits. The image below shows their characteristic cusped chewing surface.

Mastodons looked like elephants but are actually in a separate family (Mammutidae instead of Proboscidea). They browsed diverse vegetation rather than grazed like elephants and mammoths. The American Mastodon roamed most of North America. They lived in herds in the cool woodlands, probably meeting final extinction under the spears of Paleo-Indians about 10,000 years ago.

My favorite reproduction of the American Mastodon is shown below. It is by the famous scientific illustrator Charles R. Knight (1874-1953). There is something very spirited as this young male charges into the scene. It even looks a bit like northeastern Ohio.

Wooster’s Fossil of the Week: A sweet local scallop (Lower Carboniferous of Wooster)

March 13th, 2011

The delicious scallop has a long, long history. Wooster’s variety, known as Aviculopecten subcardiformis, is about 345 million years old. The beauty above was found in the Logan Formation, a conglomeratic sandstone that underlies much of the city, including the college. This particular fossil is preserved as an external mold, meaning the shell is dissolved away and only an impression remains in the surrounding sediment. Note that this preservation is still so good that we can count all the ribs and even growth lines.

Scallops are characterized by a nearly-symmetrical shell. They have extensions along the hingeline (at the top of the image) that are commonly called “ears” and technically termed auricles. They have one large muscle (adductor) used to close the shell. It is relatively large and the part of the clam we find so tasty.

Pecten jacobaeus from the Mediterranean Sea. (Photo courtesy of Andreas Tille of en.wikipedia.)

Many modern scallops use that large adductor muscle to clap the valves together when they are threatened, enabling them to swim short distances. As an early warning system to detect predators (including us, I suppose), they have rows of tiny eyes in the soft tissue around the edge of the shell (see below).

The eyes of this living scallop are the small bluish spheres along the edge of the mantle.

We can’t tell if our ancient scallop was able to see its enemies and swim away. It does, though, take us back to a time when a warm shallow sea covered our little patch of Ohio.

Theory to Practice on Ice

February 1st, 2011

A group from the Wooster community, the University of Cincinnati, The College of Wooster and St. Lawrence University assembled in Wooster for the weekend to mount an expedition to recover many meters of lake mud from the bottom of Round and Long Lakes in Ashland County, Ohio.

Dr. Lowell goes over the theory.

The practice consists of extracting meters of mud from the lake bottom.

Steph takes the vital notes on each meter (left). Lindsey (right) steps up to core another hole in the 6 inch-thick ice.

After a day coring Round Lake the team moved onto Long Lake and targeted the upper several meters of sediment to be analyzed by Jon Theisen for his senior IS in Archaeology. Jon hopes to shed some light on the environmental changes that occurred approximately 1500 years ago during the end of the Hopewell era in Ohio.

Dr. Stan Totten (’58) receives a Hall of Fame award from the Ohio Department of Natural Resources

January 25th, 2011

Ston Totten (on the left) receiving the Hall of Fame award last month (image from the ODNR website).

Wooster has always been proud of its distinguished alumnus Stan Totten (’58), a retired professor of geology at Hanover College. We are now pleased to see that the state of Ohio has recognized him for his many contributions to understanding Ohio’s geology, from checking topographic maps in his early days to producing his own glacial geology and soil maps. He even provided geological expertise for the construction of Interstates 71 and 77. This nice citation from the ODNR describes Stan’s career in more detail, and as a special touch there is an embedded video of his acceptance comments.

Well done, Stan. We should mention that Stan is also in the Hanover College Athletic Hall of Fame. And in the Wayne County Sports Hall of Fame!

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