Wooster’s Fossil of the Week: A tabulate coral from the Upper Ordovician of southern Ohio

December 18th, 2015

Calapoecia huronensis Billings, 1865 top 585We have here another fossil collected by a Wooster student on the August 2015 College of Wooster Invertebrate Paleontology field trip to Caesar Creek Lake, Ohio. Eduardo Luna picked up this specimen of the tabulate coral Calapoecia huronensis (Billings, 1865) from the Waynesville Formation (Upper Ordovician). For some reason in all my years of working in the Upper Ordovician, I’ve not come across this coral species before. Eduardo had sharp eyes as you can see it is rather small. The circular tubes are corallites, each of which held a coral polyp in life. This particular coral is distinctive for its septal spines along the inside rim of each corallite, giving them a beaded appearance.

Calapoecia huronensis Billings, 1865 bottom 585This is the underside of Eduardo’s coral. The corallites on the left side are eroded, showing the elongated septal spines that run lengthwise down their inside walls.

CNSPhoto-GEOLOGISTWe met the author of C. huronensis, Elkanah Billings (1820-1876), earlier this year, but why not show the handsome Canadian again? He originally described this coral species in 1865. He was Canada’s first government paleontologist, and he very much looked the part. Billings was born on a farm near Ottawa. He went to law school and became a lawyer in 1845, but he gave up stodgy law books for the bracing life of a field paleontologist. In 1856, Billings joined the Geological Survey of Canada, eventually naming over a thousand new species in his career. The Billings Medal is given annually by the Geological Association of Canada to the most outstanding of its paleontologists.


Billings, E. 1865. Notice of some new genera and species of Palaeozoic fossils. Canadian Naturalist and Geologist, New Series 2: 432–452.

Browne, R.G. 1965. Some Upper Cincinnatian (Ordovician) colonial corals of north-central Kentucky. Journal of Paleontology 39: 1177-1191.

Cox, I. 1936. Revision of the genus Calapoecia Billings. Bulletin of the National Museum of Canada 80: 1–48.

Jull, R.K. 1976. Review of some species of Favistina, Nyctopora, and Calapoecia (Ordovician corals from North America). Geological Magazine 113: 457-467.

Wooster’s Fossil of the Week: A common trilobite from the Upper Ordovician of Ohio

December 11th, 2015

Flexicalymene meeki cephalon view 585This beautiful specimen was collected by Wooster student Eve Caudill on this year’s College of Wooster Invertebrate Paleontology field trip to Caesar Creek Lake, Ohio. It is the iconic trilobite Flexicalymene meeki (Foerste, 1910) from a soft, “buttery” shale in the Waynesville Formation (Upper Ordovician). This is one of the most common trilobite species in the world, and it has been photographed thousands of times, so I posed it at an unconventional, rakish angle. We are looking here at the cephalon (head) of the animal. I like the way the remnants of the enclosing sedimentary matrix cling to the low places, highlighting the bumps and ridges. The center of the cephalon shows the distinctive glabella with its side lobes. The stomach of the trilobite was housed underneath it. The two eyes are visible on either side of the glabella, the one on the right split by the slightly-open facial suture used for dividing its exoskeleton during molting (ecdysis).

Flexicalymene meeki pygidium view 585This is a view of the pygidium (tail end) of the same Flexicalymene meeki specimen. It is tucked under the leading edge of the cephalon in the classic enrollment position. Trilobites likely enrolled for several reasons, but the primary one was almost certainly to affect a pill-bug-like defense against predators.

Flexicalymene meeki side view 585This is a side view of the enrolled trilobite. The articulated segments between the cephalon and pygidium constitute the thorax.foerste-1936We met the author of Flexicalymene meeki four years ago in this blog, so let’s visit him again. August F. Foerste (1862-1936) was one of the pioneers of Cincinnatian paleontology and stratigraphy. He grew up and worked in the Dayton, Ohio, area. Foerste went to Denison University where he was a very successful undergraduate, publishing several geological papers. He returned to Dayton after graduation with a PhD from Harvard, teaching high school for 38 years. When he retired he was offered a teaching position at the University of Chicago, but instead went to work at the Smithsonian Institution until the end of his life.

A final note from the Invertebrate Paleontology class this year: We were greatly assisted by two fantastic paleontological websites, one by Alycia Stigall at Ohio University called The Digital Atlas of Ordovician Life, and the other by Steve Holland at the University of Georgia titled The Stratigraphy and Fossils of the Upper Ordovician near Cincinnati, Ohio. Thank you to my most excellent and productive colleagues.


Brandt, D.S. 1993. Ecdysis in Flexicalymene meeki (Trilobita). Journal of Paleontology 67: 999-1005.

Brett, C.E., Thomka, J.R., Schwalbach, C.E., Aucoin, C.D. and Malgieri, T.J. 2015. Faunal epiboles in the Upper Ordovician of north-central Kentucky: Implications for high-resolution sequence and event stratigraphy and recognition of a major unconformity. Palaeoworld 24: 149-159.

Esteve, J., Hughes, N.C. and Zamora, S. 2011. Purujosa trilobite assemblage and the evolution of trilobite enrollment. Geology 39: 575-578.

Evitt, W.R. and Whittington, H.B. 1953. The exoskeleton of Flexicalymene (Trilobita). Journal of Paleontology 27: 49-55.

Foerste, A.F. 1910. Preliminary notes on Cincinnatian and Lexington fossils of Ohio, Indiana, Kentucky, and Tennessee. Denison University Science Laboratories Bulletin 16: 17-87.

Frey, R.C. 1987. The paleoecology of a Late Ordovician shale unit from southwest Ohio and southeastern Indiana. Journal of Paleontology 61: 242-267.


Wooster’s Fossil of the Week: A spherical bryozoan from the Upper Ordovician of northeastern Estonia

October 2nd, 2015

1 Esthoniopora Kukruse 585Way back in July 2007 we had our first Team Estonia doing geological field research. Andrew Milligan (’08) and I, with our friend Dr. Olev Vinn of the University of Tartu, explored the Upper Ordovician of the northeastern part of the country, perilously close to the Russian border. Most of our work was stratigraphic and related to echinoderms, but I picked up several of these beautiful spherical bryozoans. This specimen comes from the Kiviõli Member, Viivikonna Formation, Kukruse Stage, Upper Ordovician, of Kohtla-Nõmme Quarry (N 59.35665º E 27.22343º). You won’t find the quarry on a map, though, because it was soon afterwards erased by continual mining. Now it is a grassy field. Since we are studying bryozoans this week in my Invertebrate Paleontology course, I’m bringing these specimens to the blog.

2 Esthoniopora subsphaericaThis is what two specimens of this bryozoan look like before cutting. They have the size and shape of golf balls.

3 Esthoniopora subsphaericaHere are the same two specimens cut in half and polished to show the growth rings and tubular zooecia (which held the feeding zooids of the living bryozoan).

4 Esthoniopora subsphaericaIn this closer view you can see the polygonal outlines of the zooecia, now filled with calcite. In the lower right is a boring that cut through the skeleton soon after the bryozoan’s death on the Ordovician seafloor. It has a bit of sediment that filled the boring except for the very center, which apparently held the body of the borer.

This bryozoan is the trepostome Esthoniopora subsphaerica (Bassler, 1911). Bassler originally called it Hemiphragma subsphaericum, which is a nod to its abundant hemiphragms (curving partitions in the zooecial tubes). As bryozoans go, this one has a fairly simple structure with no exozone, endozone, monticules or spines. How it lived on the seafloor with such a spherical shape is a bit of a mystery. A slightly flattened patch is probably where the sphere contacted the sediment. The borings in these bryozoans were studied by Wyse Jackson and Key (2007).

5 Ray BasslerThe species author, Raymond S. Bassler (1878-1961), was an American paleontologist prominent in the study of bryozoans and other encrusting organisms. He was born in Philadelphia and became very interested in fossils from childhood. He received his bachelor’s degree from that paleontological bastion the University of Cincinnati in 1902, followed quickly by his master’s (1903) and PhD (1905) degrees from George Washington University, where he served as a professor for over forty years. He also began work at the United States National Museum in Washington in 1910, rising through the ranks to become Head Curator in 1929. His main interests were bryozoans from the Cenozoic of the Gulf and Atlantic coasts, on which he had long collaborations with the French bryozoologist Ferdinand Canu. He also worked closely with Charles Schuchert, Carl Ludwig Rominger, and Edward Oscar Ulrich. Ray Bassler died in 1961.


Bassler, R.S. 1911. The Early Paleozoic Bryozoa of the Baltic Provinces. Bulletin of the US National Museum 77: 1-382.

Koromyslova, A.V., Fedorov, P.V. and Ershova, V.B. 2009. New records of bryozoans from the Lower Ordovician of the Leningrad Region and intercolonial variability in Esthoniopora lessnikowae (Modzalevskaya). Paleontological Journal 43:39–45.

Wyse Jackson, P.N. and Key, M.M. 2007. Borings in trepostome bryozoans from the Ordovician of Estonia: two ichnogenera produced by a single maker, a case of host morphology control. Lethaia 40: 237-252.

Wooster’s Fossil of the Week: A starry bryozoan from the Upper Ordovician of southern Ohio

September 11th, 2015

Constellaria polystomella Liberty Formation 585At this time of the year I pick out one interesting specimen from the fossils my Invertebrate Paleontology class collected on their first field trip into the Upper Ordovician of southern Ohio. They did so well this week that I may be choosing a few more later! Our Fossil of the Week is the above bryozoan given the beautiful name Constellaria polystomella Nicholson, 1875. It was found by Jacob Nowell at the Caesar Creek Emergency Spillway in the Liberty Formation.
Constellaria Liberty closerConstellaria is a beautiful form, and one of the easiest bryozoans to recognize. Like all bryozooans, it was a colonial invertebrate with hundreds of filter-feeding individuals (zooids) housed in tiny tubes called zooecia. In Constellaria some of the zooecia are regularly grouped together and raised into star-shaped bumps called monticules. (The name Constellaria is clever.) This genus is a cystoporate bryozoan in the Family  Constellariidae.
JD Dana by Daniel Huntington 1858I was surprised to learn that Constellaria was named in 1846 by James Dwight Dana (1813-1895), one of the most accomplished American scientists of the 19th Century. He is best known for his Manual of Mineralogy (1848) which is still in print (greatly revised) and known as “Dana’s Mineralogy”. Dana (shown above in 1858) studied geology on scales from crystal structures to continents, with volcanoes and mountain-building in between. He had an affinity for “Zoophytes” (animals that appear to be plants), thus entangled him briefly with bryozoan systematics. Dana was born in Utica, New York, and attended Yale College, working under Benjamin Silliman, a famous chemist and mineralogist. After graduating from college he had a cool job teaching midshipmen in the US Navy, sailing through the Mediterranean in the process. For four years he served in the United States Exploring Expedition in the Pacific region. He made numerous important geological observations in Hawaii and the Pacific Northwest that he later published in books and papers. He even dabbled in theology with books like Science and the Bible: A Review of the Six Days of Creation (1856). Dana died in 1895 having received numerous accolades and awards for his research and writing.


Brown, G.D., Jr., and Daly, E.J. 1985. Trepostome bryozoa from the Dillsboro Formation (Cincinnatian Series) of southeastern Indiana. Indiana Geological Survey Special Report 33: 1-95.

Cutler, J.F. 1973. Nature of “acanthopores” and related structures in the Ordovician bryozoan Constellaria. Living and Fossil Bryozoa. Academic Press, London, 257-260.

Dana J.D. 1846. Structure and classification of zoophytes. U.S. Exploring Expedition 1838-1842, 7: 1-740.

Wooster Paleontologists return to Caesar Creek Lake

September 6th, 2015

1 Shoreside collecting 090615Ohio is a wonderful place for paleontologists. One of the reasons is the thick, productive set of Upper Ordovician rocks that are exposed in the southwest of the state in and around Cincinnati. It is an easy drive south from Wooster into some of the most fossiliferous sediments in the world. Today Wooster’s Invertebrate Paleontology class went to Caesar Creek Lake in Warren County with its shoreline and emergency spillway exposing richly productive limestones and shales of the Waynesville, Liberty and Whitewater Formations (all of which equal the Bull Fork Formation). I’ve been there many times with many classes. The weather today was hot and dry — a contrast with last year’s torrential rains and mud.

2 Caesar Creek Lake Visitor Center MS 090615After a three-hour drive, we stopped first at the U.S. Army Corps of Engineers visitor center for Caesar Creek Lake. The Corps built the dam and spillway for the lake, and continues to maintain them both. This center has a set of museum displays and is where we obtain our fossil collecting permit. (This image was taken by Mara Sheban, a sophomore at The College of Wooster who will be contributing photographs to this blog and other geology projects.)

3 Initial briefing MS 090615Our initial briefing, with a review of the local geology and most common fossils. Since this is the start of the Invertebrate Paleontology course, most students have only begun to explore the topic. The fossils they collect on this trip will be the basis of a semester-long project of systematics and paleoecological analysis. (Photo by Mara Sheban.)

4 Marching to the outcrop 090615Our march to the far north of the exposures at the Caesar Creek Lake emergency spillway. We actually drop down from the spillway to the lake’s south shore. (See photo at the top of this post.) In the distant parking lot you can just make out a white pick-up truck in which the seasonal ranger is keeping an eye on us.

5 Jacob Nowell collecting MS 090615Jacob Nowell collecting small fossils washed from the shale along the lakeshore. (Photo by Mara Sheban.)

6 Jacob Pries trilobite MS 090615Jacob Pries found a nice enrolled Flexicalymene trilobite. Caesar Creek has a reputation as being a good place to find trilobites. We love them, but are also interested in the rest of the fossil fauna. (Mara Sheban image.)

7 Brachiopod hash 090615Some of the limestone units are a nearly solid hash of cemented brachiopod shells.

8 Hardground full view 0090616My favorite slabs at Caesar Creek Lake are the abundant carbonate hardgrounds like the above. A hardground is a cemented seafloor, usually with borings and encrusting organisms. This one began as a burrowed soft carbonate sediment. The burrows were filled with fine mud that cemented early on the seafloor. The surrounding softer matrix washed away, leaving a hardground with the burrows now in positive relief. Brachiopods and corals then lived in the nooks and crannies of this hard rock on the bottom of the sea.

9 Hardground closer 090615Here is the burrow system in a closer view. In the upper right is a beautiful encrusted rugose coral, shown in detail below.

10 Bryo encrusted rugosan 090615That coral is almost completely covered by a trepostome bryozoan. I would have loved to collect this specimen for further study, but the slab is too large and no tools are allowed on this outcrop.

In the coming weeks we will identify the fossils we gathered, apply to them several paleontological techniques such as cleaning, cutting, polishing and photography, and then put together a grand paleoecological analysis. We will be greatly assisted by two fantastic websites, one by Alycia Stigall at Ohio University called The Digital Atlas of Ordovician Life, and the other by Steve Holland at the University of Georgia titled The Stratigraphy and Fossils of the Upper Ordovician near Cincinnati, Ohio.

Wooster’s Fossil of the Week: Small and common orthid brachiopods from the Upper Ordovician of Ohio

August 7th, 2015

Cincinnetina meeki (Miller, 1875) slab 1 585
One of the many benefits of posting a “Fossil of the Week” is that I learn a lot while researching the highlighted specimens. I not only learn new things, I learn that some things I thought I knew must be, shall we say, updated. The above slab contains dozens of brachiopods (and a few crinoid ossicles and bryozoans). I have long called the common brachiopod here Onniella meeki. Now I learn from my colleagues Alycia Stigall and Steve Holland at their great Cincinnatian websites that since 2012 I should be referring to this species as Cincinnetina meeki (Miller, 1875). Jisuo Jin sorted out its taxonomy in a Palaeontology article three years ago:

Phylum: Brachiopoda
Class: Rhynchonellata
Order: Orthida
Family: Dalmanellidae
Genus: Cincinnetina
Species: Cincinnetina meeki (Miller, 1875)
Cincinnetina meeki (Miller, 1875) slab 2 585This slab, which resides in our Geology 200 teaching collection, was found at the famous Caesar Creek locality in southern Ohio. It is from the Waynesville/Bull Fork Formation and Richmondian (Late Ordovician) in age.
Cincinnetina meeki (Miller, 1875) slab 3 585You may see some bryozoans in this closer view. This bed is a typical storm deposit in the Cincinnatian Group. The shells were tossed about, most landing in current-stable conditions, and finer sediments were mostly washed away, leaving this skeletal lag.


Jin, J. 2012. Cincinnetina, a new Late Ordovician dalmanellid brachiopod from the Cincinnati type area, USA: implications for the evolution and palaeogeography of the epicontinental fauna of Laurentia. Palaeontology 55: 205–228.

Wooster’s Fossils of the Week: An Upper Ordovician cave-dwelling bryozoan fauna and its exposed equivalents

July 3rd, 2015

1 Downwards 063015This week’s fossils were the subject of a presentation at the 2015 Larwood Symposium of the International Bryozoology Association in Thurso, Scotland, last month. Caroline Buttler, Head of Palaeontology at the National Museum Wales, Cardiff, brilliantly gave our talk describing cryptic-and-exposed trepostome bryozoans and their friends in an Upper Ordovician assemblage I found years ago in northern Kentucky. They were the subject of an earlier Fossil of the Week post, but Caroline did so much fine work with new thin sections and ideas that they deserve another shot at glory. We are now working on a paper about these bryozoans and their borings. Below you will find the abstract of the talk and a few key slides to tell the story.


Trepostome bryozoans have been found as part of an ancient cave fauna in rocks of the Upper Ordovician (Caradoc) Corryville Formation exposed near Washington, Mason County, Kentucky.

Bryozoans are recognized as growing from the ceiling of the cave and also from an exposed hardground surface above the cave. Multiple colonies are found overgrowing one another and the majority are identified as Stigmatella personata. Differences between those growing upwards and those growing down from the roof have been detected in the limited samples.

The colonies have been extensively bored, these borings are straight and cylindrical. They are identified as Trypanites and two types are recognised. A smaller variety is confined within one colony overgrowth and infilled with micrite. In thin section it is observed that the borings follow the lines of autozooecial walls and do not cut across. This creates a polygonal sided boring, suggesting that the colonies were not filled with calcite at the time of the boring. The second variety has a larger tube size and its infilling sediment has numerous dolomite rhombs and some larger fossil fragments including cryptostomes, shell and echinoderm pieces. These cut through several layers of overgrowing bryozoans. Some of the borings contain cylindrical tubes of calcite similar to the ‘ghosts’ of organic material described by Wyse Jackson & Key (2007).

Very localised changes in direction of colony growth due to an environmental effect are seen.

Bioclaustration in these samples provides evidence for fouling of the colony surface, indicating that the bryozoans overgrew unknown soft-bodied organisms.


Wyse Jackson, P. N., and M. M. Key, Jr. (2007). Borings in trepostome bryozoans from the Ordovician of Estonia: two ichnogenera produced by a single maker, a case of host morphology control. Lethaia. 40: 237-252.

2 Title 0630153 Location 0630154 Strat position 0630155 hdgd up 0630156 hdgd down 0630157 Growth up 0630158 Growth down 0630159 Stigmatella 06301510 Cartoon 06301511 Boring A 06301512 Boring B 06301513 Ghosts explanation14 Ghosts 06301515 Overgrowths 06301516 Further questions 063015

Wooster’s Fossils of the Week: An encrusted bivalve external mold from the Upper Ordovician of Indiana

June 26th, 2015

1 Anomalodonta gigantea Waynesville Franklin Co IN 585I love this kind of fossil, which explains why you’ve seen so many examples on this blog. We are looking at an encrusted external mold of the bivalve Anomalodonta gigantea found in the Waynesville Formation exposed in Franklin County, Indiana. I collected it many years ago as part of an ongoing study of this kind of preservation and encrustation.
2 Anomalodonta gigantea Waynesville Franklin Co IN 585 annotatedTo tell this story, I’ve lettered the primary interest areas on image above. First, an external mold is an impression of the exterior of an organism. In this case we have a triangular clam with radiating ribs in its shell. The exterior of the shell with its ribs was buried in sediment and the shell dissolved, leaving the basic impression above. It is a negative relief. Please now refer to the letters for the close-up images below.

3 Bryo Anomalodonta gigantea Waynesville Franklin Co INA. At the distal end of the bivalve mold is what looks at first to be the original shell. It is calcitic, though, and we know this bivalve had an aragonitic shell. A closer look shows that this is actually the attaching surface of an encrusting bryozoan that bioimmured the original bivalve shell, which has since dissolved away. This smooth surface is the bryozoan underside; we see the characteristic zooecia (tubes holding the individual zooids) only when this surface is weathered away.

4 Borings Anomalodonta gigantea Waynesville Franklin Co INB. These tubular objects are infillings of borings (maybe Trypanites)that were cut into the original aragonitic shell of the bivalve. The tunnels of the borings were filled with fine sediment, and then the shell dissolved away, leaving these casts of the borings.

5 Inarticulate scar Anomalodonta gigantea Waynesville Franklin Co INC and D. In the middle of the external mold is this curious circular feature (C) mostly surrounded by a bryozoan (D). There was at one time a circular encruster, likely an inarticulate brachiopod like Petrocrania, that sat directly on the external mold surface. The bryozoan colony grew around but not over it because it was alive and still opening and closing its valves for feeding. The bryozoan built a vertical sheet of skeleton around it as a kind of sanitary wall. You may be able to see the other three or four structures in the top image showing brachiopod encrusters that left the building. This is an example of fossils showing us a living relationship, even if one is not longer preserved.

This fossil and its sclerobionts (hard substrate dwellers) show us that soon after the bivalve died its aragonitic shell dissolved away, leaving as evidence the external mold in the sediment, the bioimmuring bryozoan, and the boring casts. Very soon thereafter bryozoans and brachiopods encrusted the available hard substrate. This is a typical example of early aragonite dissolution on the sea floor during a Calcite Sea interval.


Palmer, T.J. and Wilson, M.A. 2004. Calcite precipitation and dissolution of biogenic aragonite in shallow Ordovician calcite seas. Lethaia 37: 417-427.

Taylor, P.D. 1990. Preservation of soft-bodied and other organisms by bioimmuration—a review. Palaeontology 33: 1-17.

Taylor, P.D. and Wilson, M.A. 2003. Palaeoecology and evolution of marine hard substrate communities. Earth-Science Reviews 62: 1-103.

Wilson, M.A., Palmer, T.J. and Taylor, P.D. 1994. Earliest preservation of soft-bodied fossils by epibiont bioimmuration: Upper Ordovician of Kentucky. Lethaia 27: 269-270.

Wooster’s Fossil of the Week: An undescribed cyclostome bryozoan from the Upper Ordovician of Oklahoma

June 19th, 2015

HT_1276 585Paul Taylor and I presented a talk this month at the Larwood Symposium of the International Bryozoology Association in Thurso, Scotland. (Yes, way in the tippy-top of Scotland. Very cool.) Paul found the above wiggly bryozoan encrusting the interior of an orthid brachiopod identified as Multicostella sulcata (thanks, Alycia Stigall!) in the Lower Echinoderm Zone of the Mountain Lake Member of the Bromide Formation (Upper Ordovician, Sandbian) near Fittstown, Oklahoma. This bryozoan is “new to science”, as we grandly say. Paul generously invited me to describe it with him in this presentation and in a future paper. We did a 1994 paper together on Corynotrypa, a similar cyclostome bryozoan. The following are a few slides from our Larwood talk.






Slide21_052815This last image showing what appear to be an interior wall with a pore is critical. Corynotrypa does not have such walls, so our bryozoan is more like a sagenellid cyclostome.


Carlucci, J.R., Westrop, S.R., Brett, C.E. and Burkhalter, R. 2014. Facies architecture and sequence stratigraphy of the Ordovician Bromide Formation (Oklahoma): a new perspective on a mixed carbonate-siliciclastic ramp. Facies 60: 987-1012.

Taylor, P.D. and Wilson, M.A. 1994. Corynotrypa from the Ordovician of North America: colony growth in a primitive stenolaemate bryozoan. Journal of Paleontology 68: 241-257.

Wooster’s Fossil of the Week: A bored and formerly encrusting trepostome bryozoan from the Upper Ordovician of Indiana

March 20th, 2015

1 Trep Upper 030115The lump above looks like your average trepostome bryozoan from the Upper Ordovician. I collected it from the Whitewater Formation of the Cincinnatian Group at one of my favorite collecting sites near Richmond, Indiana. In this view you can just barely make out the tiny, regular holes that are the zooecia (calcitic tubes that held the bryozoan individuals — the zooids). There are bits of other fossils stuck to the outside, so it’s not particularly attractive as fossils go. (Except that all fossils are fascinating messengers in time.)

2 Trep Upper CloseWith this closer view you can see my initial interest in this particular bryozoan. Again, the regular, tiny holes are the zooecia. The larger pits are borings by worm-like, filter-feeding organisms. These borings are either in the ichnogenus Trypanites (if they are cylindrical) or Palaeosabella (if they are clavate, meaning clubbed at their distal ends). Such borings are common in all types of skeletal fossils in the Upper Ordovician — so common that they are part of the evidence for the Ordovician Bioerosion Revolution. So, let’s flip this ordinary, bored bryozoan over and see what’s underneath:

3 Trep Under 030115Here’s the main scientific beauty! We’re looking at the underside of the bryozoan. Ordinarily we’d expect to see a shell here that the bryozoan was encrusting, but the shell is gone. We’re gazing directly at the attachment surface of the bryozoan. It’s as if the colony had encrusted a sheet of glass and we’re looking right through it. The shell it was originally attached to has been removed either through dissolution (it might have been an aragonitic bivalve) or physical removal (it may have been a calcitic brachiopod). The borings are now much more prominent. They penetrated through the bryozoan into the mysterious missing shelly substrate. Some are small pits that just intersected the shell, others are horizontal as the boring organism turned at a right angle when it reached the shell and drilled along the bryozoan-shell interface. Removing the shell exposed the distal parts of these borings — parts that ordinarily would have been hidden by the encrusted shell.

4 Trep Under labeledHere is a closer, labeled view of this bryozoan basal surface. A is the earliest encruster recorded in this scenario; it is a small encrusting bryozoan that was first on the shelly substrate and then completely overgrown (or bioimmured) by the large trepostome. B shows that the trepostome was growing on a shell that already had borings from a previous encruster-borings combination that must have fallen off; these are grooves in the substrate that the trepostome filled in as it covered the shell. C is one of the many later borings that cut perpendicularly through the bryozoan and worked along the shell-bryozoan interface; as described above, only when that shelly substrate was removed would these be visible. In this surprisingly complex story, B represents an earlier version of C. We thus know that the shell was encrusted by one bryozoan, bored, and then that bryozoan was freed at its attachment (and not found in our collection). The same shell was then encrusted by this second bryozoan, which recorded the groove (or “half-borings”) made during the first encrustation.

These half-borings were first described in 2006 when my students Cordy Dennison-Budak and Jeff Bowen worked with me on them and we had a GSA abstract. Coleman Fitch is presently completing his Senior Independent Study enlarging the database for these features and developing detailed interpretations. The main implication from this work is that thick trepostome bryozoan encrusters often “popped off” shells, leaving no signs of their presence unless there were these half-borings in the shell surfaces and bryozoan undersides. Paleoecology and taphonomy on a very small scale!


Taylor, P.D. 1990. Preservation of soft-bodied and other organisms by bioimmuration—a review. Palaeontology 33: 1-17.

Wilson, M.A., Dennison-Budak, W.C., and Bowen, J.C. 2006. Half-borings and missing encrusters on brachiopods in the Upper Ordovician: Implications for the paleoecological analysis of sclerobionts. Geological Society of America Abstracts with Programs, Vol. 38, No. 7, p. 514.

Wilson, M.A. and Palmer, T.J. 2006. Patterns and processes in the Ordovician Bioerosion Revolution. Ichnos 13: 109-112.

Wilson, M.A., Palmer, T.J. and Taylor, P.D. 1994. Earliest preservation of soft-bodied fossils by epibiont bioimmuration: Upper Ordovician of Kentucky. Lethaia 27: 269-270.


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