Wooster’s Fossil of the Week: a beautiful phacopid trilobite (Middle Devonian of Ohio, USA)

August 5th, 2012

Trilobites are always favorite fossils, especially big bug-eyed ones like Phacops rana (Green, 1832) shown above. It is, in fact, the state fossil of Pennsylvania after a petition from schoolchildren in 1988. This specimen is from the Middle Devonian of northwestern Ohio. Trilobites were Paleozoic arthropods with a hard dorsal skeleton divided into numerous segments. They look rather cute and brainy because of a swelling between the eyes (the glabella), but that space prosaically contained the stomach. Many trilobites, like this one, could roll up into balls when stressed, much like pill bugs today.

Phacops was studied by paleontologist Niles Eldredge in the early 1970s as the start of what became the theory of punctuated equilibria. The arrangement of lenses in the eyes show rapid changes in short intervals of geological time, which provided evidence for the theory he presented with colleague Stephen Jay Gould.

Phacops rana was named by Jacob Green in 1832. He called it Calymene bufo rana. Hall (1861) renamed it Phacops rana, which was confirmed by Eldedge (1972). Struve (1990) placed it in the new genus Eldredgeops (named after you know who), but I prefer the older name.
Jacob Green (1790-1841) was one of those early 19th Century American polymaths. He was a lawyer, a chemist, a physician, an astronomer, and a paleontologist. He came from a religious family, with both his father and grandfather being theologians. His father, in fact, was at one time president of Princeton University. Jacob graduated from the University of Pennsylvania at the young age of 16, and he published a treatise on electricity when he was 19. He did lawyering for a few years before becoming a professor at (you guessed it) Princeton (and later Jefferson Medical College). He published an amazing array of diverse scientific papers in his career. A trip to England introduced him to trilobites. He then spent a decade putting together a monograph on the trilobites of North America — the first ever.


Eldredge, N. 1972. Systematics and evolution of Phacops rana (Green, 1832) and Phacops iowensis Delo, 1935 (Trilobita) for the Middle Devonian of North America. Bull. Am. Mus. Nat. Hist. 147:45-114.

Eldredge, N. 1973. Systematics of Lower and Lower Middle Devonian species of the trilobite Phacops Emmrich in North America. Bull. Am. Mus. Nat. Hist. 151:285-338.

Green, J. 1832. A Monograph of the Trilobites of North America. Philadelphia.

Hall, J. 1861. Descriptions of new species of fossils from the Upper Helderberg, Hamilton, and Chemung Groups. N.Y. State Cab. Nat. Hist., Ann. Rept. No. 14.

Struve, W. 1990. Paläozoologie III (1986-1990). Courier Forschungsinstitut Senckenberg 127: 251-279.

Wooster’s Fossil of the Week: An asteroid trace fossil from the Devonian of northeastern Ohio

February 12th, 2012

It is pretty obvious what made this excellent trace fossil: an asteroid echinoderm. (The term “asteroid” sounds odd here, but it is the technical term for a typical sea star.) The above is Asteriacites stelliformis Osgood, 1970, from the Chagrin Shale (Upper Devonian) of northeastern Ohio.

We can tell that it was made by a sea star burrowing straight down into the sediment because it has faint chevron-shaped marks in the rays made by tube feet as they moved sediment aside. The mounds of excavated sediment can be seen between the rays at their bases. This tells us that we are not looking at an external mold of a dead sea star, but instead its living activity. This is what a trace fossil is all about.

A living asteroid from the shallow sea off Long Island, The Bahamas. (The hand belongs to my son, Ted Wilson.)

The ichnogenus Asteriacites was named by von Schlotheim in 1820. We profiled him earlier with the genus Cornulites. The author of Asteriacites stelliformis was Richard G. Osgood, Jr., my undergraduate advisor and predecessor paleontologist at The College of Wooster.
Richard Osgood, Jr., was born in Evanston, Illinois, in 1936. He went to Princeton for his undergraduate degree (I still remember his huge Princeton ring) and received his Ph.D. from the University of Cincinnati. He worked for Shell Oil Company in Houston just prior to joining the Wooster faculty in 1967. He was one of the pioneers of modern ichnology (the study of trace fossils), naming numerous new ichnotaxa and providing ingenious interpretations of them. At least one trace fossil was named after him: Rusophycus osgoodii Christopher, Stanley and Pickerill, 1998. Dr. Osgood died in 1981 in Wooster. He was an inspiration to me and many other Wooster geology students during his productive career, which was all too short.


Osgood, R.G., Jr. 1970. Trace fossils of the Cincinnati area. Palaeontographica Americana 6: 281-444.

Schlotheim, E.F. von. 1820. Die Petrfactendunde auf ihrem jetzigen Standpunkte durch die Beshreibung seiner Sammlung versteinerter und fossiler Überreste des Thier- und Pflanzernreichs der Vorwelt erläutert 1-457.

Stanley, D.C.A. and Pickerill, R.K. 1998. Systematic ichnology of the Late Ordovician Georgian Bay Formation of southern Ontario, eastern Canada. Royal Ontario Museum Life Sciences Contribution 162, 56 pp., 13 pl. Toronto.

Wooster’s Fossils of the Week: Bivalve escape trace fossils (Devonian and Cretaceous)

January 29th, 2012

It is time again to dip into the wonderful world of trace fossils. These are tracks, trails, burrows and other evidence of organism behavior. The specimen above is an example. It is Lockeia James, 1879, from the Dakota Formation (Upper Cretaceous). These are traces attributed to infaunal (living within the sediment) bivalves trying to escape deeper burial by storm-deposited sediment. If you look closely, you can see thin horizontal lines made by the clams as they pushed upwards. These structures belong to a behavioral category called Fugichnia (from the Latin fug for “flee”). They are excellent evidence for … you guessed it … ancient storms.
The specimens above are also Lockeia, but from much older rocks (the Chagrin Shale, Upper Devonian of northeastern Ohio). Both slabs show the fossil traces preserved in reverse as sediment that filled the holes rather than the holes themselves. These are the bottoms of the sedimentary beds. We call this preservation, in our most excellent paleontological terminology, convex hyporelief. (Convex for sticking out; hyporelief for being on the underside of the bed.)

The traces we know as Lockeia are sometimes incorrectly referred to as Pelecypodichnus, but Lockeia has ichnotaxonomic priority (it was the earliest name). Maples and West (1989) sort that out for us.
Uriah Pierson James (1811-1889) named Lockeia. He was one of the great amateur Cincinnatian fossil collectors and chroniclers. In 1845, he guided the premier geologist of the time, Charles Lyell, through the Cincinnati hills examining the spectacular Ordovician fossils there. He was the father of Joseph Francis James (1857-1897), one of the early systematic ichnologists.


James, U.P. 1879. The Paleontologist, No. 3. Privately published, Cincinnati, Ohio. p. 17-24.

Maples, C.G. and Ronald R. West, R.R. 1989. Lockeia, not Pelecypodichnus. Journal of Paleontology 63: 694-696.

Radley, J.D., Barker, M.J. and Munt, M.C. 1998. Bivalve trace fossils (Lockeia) from the Barnes High Sandstone (Wealden Group, Lower Cretaceous) of the Wessex Sub-basin, southern England. Cretaceous Research 19: 505-509.

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.


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.

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.



Wooster’s Fossil of the Week: A tabulate coral (Middle Devonian of New York)

September 4th, 2011

This week’s specimen is from a group of fossils I gave my Invertebrate Paleontology students as “unknowns” to identify. Since it is their very first week of class I expected them to struggle, but many did remarkably well. (Congratulations to Lauren Vargo and Kit Price for correctly identifying it to the genus level, and to Lauren for hitting the species itself!)

Pleurodictyum americanum Roemer 1876 is pictured above with a view of its living surface. It is a tabulate coral belonging to the Family Favositidae, thus another type of “honeycomb coral” as we’ve discussed before on this blog. This particular species is notable because it is very common in the Middle Devonian of the northeastern United States (Pandolfi and Burke, 1989). Brian Bade collected this coral, along with hundreds of others, from the Kashong Shale exposed in Livingston County, New York. He generously donated it to the paleontological teaching and research collection at Wooster.

What is most interesting about these corals is that they are almost always found with an external mold of a elongate snail shell on the underside at their origin. The snail (more officially called a gastropod) is Palaeozygopleura hamiltoniae (Hall, 1860), and it is best known for its tight relationship with Pleurodictyum americanum. Brett and Cottrell (1982) published a detailed study of P. americanum and its associates, concluding that the coral preferred to encrust P. hamiltoniae shells but only when the snail itself was dead and gone and the shell was occupied by some other organism.
Pleurodictyum americanum underside showing an external mold of the gastropod Palaeozygopleura hamiltoniae.

Closer view of Palaeozygopleura hamiltoniae.

Pleurodictyum americanum was described by Carl Ferdinand von Roemer in 1876. Roemer was a German geologist (you probably guessed) who lived from 1818 to 1891 — a time interval encompassing some of the greatest changes in the Earth Sciences, from the primacy of Charles Lyell to the general acceptance of Darwinian evolution. Roemer was educated at Göttingen to be a lawyer, but in 1840 abandoned the legal profession for the much more exciting life of a geologist. He quickly obtained one of those new-fangled German PhD degrees in 1842 and set to work.
Roemer’s original 1876 drawings of Pleurodictyum americanum.

In 1845, Roemer traveled to the USA and studied the geology of Texas and other southern states. That must have been an adventure — the Battle of the Alamo was less than ten years before. It was during the American work that he began to describe Devonian fossils, including our coral species (Roemer, 1876). Roemer became a professor of geology, paleontology and mineralogy (another field in which he had significant accomplishments) at the Universty of Breslau, where he ended his career.

Carl Ferdinand von Roemer (1818 to 1891) at the University of Breslau (now the University of Wrocław in Poland).


Brett, C.E. and Cottrell, J.F. 1982. Substrate specificity in the Devonian tabulate coral Pleurodictyum. Lethaia 15: 247-262.

Pandolfi, J.M. and Burke, C.D. 1989. Environmental distribution of colony growth form in the favositid Pleurodictyum americanum. Lethaia 22: 69–84.

Roemer, F. von. 1876. Lethaea geognostica: Handbuch der erdgeschichte mit Abbildungen der für die formationen bezeichnendsten Versteinerungen, I. Theil. Lethaea palaeozoica. E. Schweizerbartsche Verlagshandlung (E. Koch), Stuttgart, Germany.

Quality time with a Polish microscope

June 21st, 2011

SOSNOWIEC, POLAND–A day in the lab with my colleague Michał Zatoń at the University of Silesia. We sorted through two very different paleontological problems with a microscope and a lot of hand waving. The first task was to come up with a hypothesis about the origin of the strange pitted tubes shown above. They are found on hiatus concretions of the Late Bathonian (Middle Jurassic) exposed in Zarki, Poland. We recently described and analyzed the sclerobionts on and in these concretions (see Zaton et al., 2011), but these tubes remained a mystery. We think now that they are remnants of egg cases laid by gastropods (snails) on the undersurfaces of the concretions, and we’ve started on the manuscript.

The coiled encrusting shell below is of a Devonian microconchid originally collected by the keen amateur Brian Bade in western New York and generously donated to our research. This group has some fascinating similarities and differences from its Polish cousins, so we have started a systematic project to determine if they represent a new genus or not. (Brian will be excited to hear this.)

Michal's office/lab in the Faculty of Earth Sciences, University of Silesia.

Tomorrow we set off for fieldwork in the area so I’ll post pictures of the wonderful Polish countryside!


Zatoń, M., Machocka, S., Wilson, M.A., Marynowski, L. and Taylor, P.D. 2011. Origin and paleoecology of Middle Jurassic hiatus concretions from Poland. Facies 57: 275-300.

Wooster’s Fossil of the Week: Mysterious tentaculitids (Devonian of Maryland)

May 29th, 2011

The sharp little conical fossils above are common Paleozoic fossils, especially in the Devonian. They are tentaculitids now most commonly placed in the Class Tentaculitoidea Ljashenko 1957. Tentaculitids appeared in the Ordovician and disappeared sometime around the end of the Carboniferous and beginning of the Permian. These specimens are from the Devonian of Maryland.

The systematic placement of the tentaculitids has been controversial. Their straight, narrow shells are usually ornamented by concentric rings, and many had septa (thin shelly partitions) inside the cones. The microstructure of the shells is most interesting — it looks very much like that of brachiopods and bryozoans. For this reason and several others, several of my colleagues and I believe the tentaculitids were lophophorates (animals that filter-feed with a tentacular device called a lophophore). They may thus be related to other problematic tubeworms like microconchids and cornulitids (Taylor et al., 2010).

Tentaculitids from the New Creek Limestone (Lochkovian, Early Devonian) of New Creek, West Virginia.

Knowing how the tentaculitids fit into an evolutionary scheme, though, has not helped us figure out what they did for a living. The figure below, from Cornell et al. (2003), shows these funny cones in just about every lifestyle imaginable!


Cornell, S.R., Brett, C.E. and Sumrall, C.D. 2003. Paleoecology and taphonomy of an edrioasteroid-dominated hardground association from tentaculitid limestones in the Early Devonian of New York: A Paleozoic rocky peritidal community. Palaios 18: 212-224.

Taylor, P.D., Vinn, O. and Wilson, M.A. 2010. Evolution of biomineralization in ‘lophophorates’. Special Papers in Palaeontology 84: 317-333.

Wooster’s Fossil of the Week: The tabulate coral Aulopora (Devonian of northwestern Ohio)

January 2nd, 2011

We’re going to start 2011 with a new blog feature: Fossil of the Week! My colleagues, of course, are welcome to also start “Mineral of the Week”, “Structural Geologic Feature of the Week”, or “Climate Event of the Week”.  The more the better to keep our blog active through the winter!

This week’s fossil was collected by Brian Bade of Sullivan, Ohio, and donated to Wooster as part of my hederelloid project.  It is a beautiful specimen of the tabulate coral Aulopora encrusting a brachiopod valve from the Silica Shale (Middle Devonian — about 390 million years old) of northwestern Ohio.  Auloporid corals are characterized by an encrusting habit, a bifurcating growth pattern, and horn-shaped corallites (individual skeletal containers for the polyps).

What is especially nice about this specimen is that we are looking at a well preserved colony origin.  The corallite marked with the yellow “P” is the protocorallite — the first corallite from which all the others are derived.  You can see that two corallites bud out from the protocorallite 180° from each other.  These two corallites in turn each bud two corallites, but at about 160°.  This pattern continues as the colony develops (a process called astogeny).  The angles of budding begin to vary depending on local obstacles; they never again go below 160°.

The polyps inside the corallites are presumed to have been like other colonial coral polyps.  Each would have had tentacles surrounding a central opening, and all were connecting by soft tissue within the skeleton.  They likely fed on zooplankton in the surrounding seawater.  This type of coral went extinct in the Permian, roughly 260 million years ago.

Again, we thank our amateur geologist friends for such useful donations to the research and educational collections in the Geology Department at Wooster.

Trays of trilobites, buckets of belemnites ….

November 26th, 2010

WOOSTER, OHIO — Last weekend we picked up another load of rocks, minerals and fossils donated by the family of one of our loyal alumni. We will be sorting through them for months getting them ready for displays and our teaching collections. Among the treasures are large numbers of particular items, especially fossils. I want to highlight two of many such sets. The trilobites are Phacops bufo from the Silica Shale (Devonian) of northeastern Ohio; the belemnites below are from the Jurassic of Wyoming. (Belemnites from the Upper Cretaceous of Germany and the Jurassic of Israel have been featured in this blog, as have beautiful trilobites from the Middle Cambrian of British Columbia, Canada.) Numerous nearly-identical fossils such as these play an important role in our teaching. We can, for example, have a fossil in front of each student during lectures for immediate reference (and quizzing!). It is also possible to have biometric measuring exercises in our labs with these fossil “populations” of particular species. Gifts again put to work in education!

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