Wooster’s Fossil of the Week: A stromatoporoid (Middle Devonian of central Ohio)

October 30th, 2011

Stromatoporoids are very common fossils in the Silurian and Devonian of Ohio and Indiana, especially in carbonate rocks like the Columbus Limestone (from which the above specimen was collected). Wooster geologists encountered them frequently on our Estonia expeditions in the last few years, and we worked with at least their functional equivalents in the Jurassic of Israel (Wilson et al., 2008).

For their abundance, though, stromatoporoids still are a bit mysterious. We know for sure that they were marine animals of some kind, and they formed reefs in clear, warm seas rich in calcium carbonate (DaSilva et al., 2011). Because of this tropical habit, early workers believed they were some kind of coral, but now most paleontologists believe they were sponges. Stromatoporoids appear in the Ordovician and are abundant into the Early Carboniferous. The group seems to disappear until the Mesozoic, when they again become common with the same form and life habits lasting until extinction in the Late Cretaceous (Stearn et al., 1999).

The typical stromatoporoid has a thick skeleton of calcite with horizontal laminae, vertical pillars, mounds on the upper surface called mamelons, and dendritic canals called astrorhizae shallowly inscribed on the mamelons. These astrorhizae are the key to deciphering what the stromatoproids. They are very similar to those on modern hard sponges called sclerosponges. Stromatoporoids appear to be a kind of sclerosponge with a few significant differences (like a calcitic instead of an aragonitic skeleton).

Stromatoporoid anatomy from Boardman et al. (1987).

Top surface of a stromatoporoid from the Columbus Limestone showing the mamelons.

There is considerable debate about whether the Paleozoic stromatoporoids are really ancestral to the Mesozoic versions. There may instead be some kind of evolutionary convergence between two groups of hard sponges. The arguments are usually at the microscopic level!

The stromatoporoids were originally named by Nicholson and Murie in 1878. This gives us a chance to introduce another 19th Century paleontologist whose name we often see on common fossil taxa: Henry Alleyne Nicholson (1844-1899). Nicholson was a biologist and geologist born in England and educated in Germany and Scotland. He was an accomplished writer, authoring several popular textbooks, and a spectacular artist of the natural world. Nicholson taught in many universities in Canada and Great Britain, finally ending his career as Regius Professor of Natural History at the University of Aberdeen.

Henry Alleyne Nicholson (1844-1899) from the University of Aberdeen museum website.

References:

Boardman, R.S., Cheetham, A.H. and Rowell, A.J. 1987. Fossil Invertebrates. Wiley Publishers. 728 pages.

DaSilva, A., Kershaw, S. and Boulvain, F. 2011. Stromatoporoid palaeoecology in the Frasnian (Upper Devonian) Belgian platform, and its applications in interpretation of carbonate platform environments. Palaeontology 54: 883–905.

Nicholson, H.A. and Murie, J. 1878. On the minute structure of Stromatopora and its allies. Linnean Society, Journal of Zoology 14: 187-246.

Stearn, C.W., Webby, B.D., Nestor, H. and Stock, C.W. 1999. Revised classification and terminology of Palaeozoic stromatoporoids. Acta Palaeontologica Polonica 44: 1-70.

Wilson, M.A., Feldman, H.R., Bowen, J.C. and Avni, Y. 2008. A new equatorial, very shallow marine sclerozoan fauna from the Middle Jurassic (late Callovian) of southern Israel. Palaeogeography, Palaeoclimatology, Palaeoecology 263: 24-29.

Wooster’s Fossil of the Week: a medullosalean pteridosperm (Upper Carboniferous of northeastern Ohio)

October 23rd, 2011

It is time we had another fossil plant in this series. The above specimen is Neuropteris ovata Hoffmann 1826, a relatively common bit of foliage in the Upper Carboniferous of North America. This is a pteridosperm, more commonly known as a seed fern. They weren’t really ferns at all but fern-like plants with some of the first real seeds. They are usually reconstructed as trees, but were also known to be bushy or even like climbing vines.

The taxonomy (naming system) of fossil plants can be very complicated because different plant parts were given different names at different times. A single plant species, then, could have a list of names for its foliage, bark, roots, seeds, etc. The name Neuropteris usually thus refers to the leaves of this particular pteridosperm.

Neuropteris ovata is famous for its use in studies of the distribution of stomata on its leaf surfaces. Stomata, sometimes called guard cells, regulate gas exchange and moisture retention in vascular land plants. The density of stomata on N. ovata leaves in the Late Carboniferous may reflect changes in carbon dioxide levels and the expansion and contraction of tropical forests (Cleal et al., 1999).

Neuropteris ovata was named by Friedrich Hoffmann (1797-1836), a Professor of Geology at the University of Berlin. I wish I knew more about him because not only did he do considerable paleobotanical research, he was also well known for his work on volcanoes in Italy. You don’t see that combination very often!

References:

Beeler, H.E. 1983. Anatomy and frond architecture of Neuropteris ovata and N. scheuchzeri from the Upper Pennsylvanian of the Appalachian Basin. Canadian Journal of Botany 61: 2352-2368.

Cleal, C.J., James, R.M. and Zodrow, E.L. 1999. Variation in stomatal density in the Late Carboniferous gymnosperm frond Neuropteris ovata. Palaios 14: 180-185.

Hoffmann, F. 1826. Untersuchungen über die Pänzen-Reste des Kohlengebirges von Ibbenbühren und von Piesberg bei Osnabrück. Archiv für Bergbau und Hüttenwesen 13: 266-282.

Zodrow, E.L. and Cleal, C.J. 1988. The structure of the Carboniferous pteridosperm frond Neuropteris ovata Hoffman. Palaeontographica Abteilung Palaophytologie 208: 105-124.

Exploring the Silica Formation (Middle Devonian) in Northwestern Ohio

October 22nd, 2011

PAULDING, OHIO–There’s nothing like the stirring rings of 50 geologic hammers in the morning. Today I was a guest of the North Coast Fossil Club and my friend Brian Bade in a quarry exposing the Middle Devonian limestones and shales. There was frost on the ground when we began, but soon the sun rose and made it a delightful fall day of fossil collecting. Thank you to Brian and the NCFC for inviting me on their trip. I’ve spoken twice to the NCFC and they have been good friends since. It was my first visit to the highly fossiliferous Silica Formation (Middle Devonian), and I came away with a bag of treasures for my classes and research projects. Thank you also to the Lafarge Cement Quarry managers for facilitating this productive experience.

The Silica Formation is very well known for its abundant fossils, especially brachiopods, corals, trilobites, and bryozoans. I’ve wanted to examine the Silica for a long time because it has produced significant material for the hederelloid and microconchid projects I have been working on with my Polish, English and Estonian colleagues. For the first time I was able to collect my own specimens of each group, and to see the fossils in their geological context.

A quarry visit always starts with a sign-in process and a reading of the rules. Note the required reflective vests and hard hats. (I was very impressed that everyone knew my name until I realized it was emblazoned on the front of my helmet.)

A wall of the quarry. The thick gray unit is the Dundee Limestone; the thin dark sequence of mixed shales and limestones at the top is the Silica Formation. Both are Middle Devonian in age (Givetian).

Most of us figured out pretty quickly that the best places to collect fossils were in the large weathered blocks in irregular piles well away from the quarry walls. The soft Silica Formation shales erode quickly, releasing the hard calcitic fossils. Climbing around on these rocks is an acquired geological skill.

My paleontology students can tell even from this distant view what kind of coral this is in the top of the Dundee Limestone. (At least they better be able to by now!)

They can also identify the order to which this beautiful and delicate bryozoan belongs, I’m certain.

Bivalves and the spiriferid brachiopod Orthospirifer in the Silica Formation.

Finally, they tend to be overlooked in the excited search for trilobites and other shelled creatures, but there are also spectacular trace fossils in the Dundee Limestone.

 

 

Fossils in the Wild: Invertebrate Paleontology Field Trip

September 11th, 2011

CAESAR CREEK LAKE, OHIO–The 2011 Invertebrate Paleontology class had a productive field trip on a beautiful Ohio day. Thunderstorms roamed the state, but we saw them only when we were comfortably on the bus.

We worked in the emergency spillway at Caesar Creek Lake in southwestern Ohio, roughly halfway between Cincinnati and Dayton. This site is maintained by the US Army Corps of Engineers as a fossil-collecting preserve. You obtain a free permit at the visitor center, agree to follow the rules, and extraordinary fossils await your picking. (Last time I was here it was very cold.)

The fossils are in the Arnheim, Waynesville, Liberty and Whitewater Formations of the Richmondian Stage in the Cincinnatian Series of the Ordovician System. These are shaly units with shell-rich limestones formed during storms. Brachiopods, bryozoans, crinoids, trilobites, clams, snails, nautiloids, corals — the whole Ordovician menagerie. Perfect for student collections and our later exercises.

Brachiopod-rich storm layer in the Liberty Formation. Note the circular bryozoan attachment.

Bryozoan colony and brachiopod shell interior from the Waynesville Formation.

Our fancy bus. The design insures that the back seats are rather bouncy.

Last of the summer flower field photos! It was such a beautiful day.

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!

References:

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.

References:

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).

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