Wooster’s Fossil of the Week: A tubeworm-encrusted parasitic gastropod (Silurian of Indiana)

February 16th, 2014

Platyostoma1_585Last week three Wooster geology students and I visited Ken Karns, an enthusiastic citizen scientist who has developed an extraordinary fossil collection in his home in Lancaster, Ohio. Ken is a man of prodigious energies and skills as he not only is an expert fossil collector and preparator, he also has a world-class curated collection of Ohio beetles! He was introduced to us by our friend Brian Bade, a man with similar enthusiasms and skills. The students were Steph Bosch (’14), Lizzie Reinthal (’14) and Ian Tulungen (’15). Our goals were to meet Ken, see his magnificent collection with Brian and other friends, and then focus on a project for Ian’s future Independent Study work. Success on all counts, and the specimen above is evidence. Ken was very generous in loaning this specimen to us along with several others for Ian’s work.

The above specimen is from the type section of the Waldron Shale Member (Silurian, Wenlockian, Homerian, about 430 million years old) of the Pleasant Mills Formation near St. Paul, south-central Indiana. Ken Karns collected and prepared it. It is a platyceratid snail of the genus Platyostoma Conrad 1842. It is probably of the species P. niagarense Hall 1852, but there is another species in the same unit (P. plebeium Hall 1876). I’m not quite sure of the differences between these species because platyceratids are notoriously variable. It is possible they are synonymous. Unlike most gastropods, platyceratids had calcite shells instead of aragonite, so they are very well preserved. For an excellent taxonomic review of the genus Platyostoma and its founder, Timothy Abbott Conrad, please see Tony Edger’s blog entry. (We’ve talked about Conrad in this blog as well.)
Platyostoma2_585In this different angle on the specimen you can see additional encrusters (sclerobionts) on the surface of the Platyostoma shell. In the lower right is a remnant of a sheet-like bryozoan, but the most prominent sclerobionts are the tubeworms Cornulites proprius Hall 1876. These encrusters interest us very much.
Cornulitids on Platyostoma_585In this closer view it is apparent that several of the cornulitids are aligned with their apertures pointing in the same way. This is a pattern we’ve seen on many of these snails. Platyostoma was a parasitic snail that lived attached to crinoids, which were abundant in the Waldron fauna. They lived high on the calyx of the crinoid firmly fixed to its skeleton. These cornulitids and other encrusters were thus living high off the substrate perched on the snails. They were filter-feeders like the crinoids, so they may have been feeding on some suspended food fraction missed by the crinoid arms, or they were competing for nutrients and added to the parasitic load on the poor crinoids. The cornulitids were further living on a living snail shell, from what we can tell, so they grew with a substrate slowly growing underneath them. This produces all sorts of delicious paleoecological questions to sort out!
Platyostoma long cornulitid_585Check out the size of this specimen of Cornulites proprius attached to another Platyostoma niagarense. Clearly these tubeworms could do very well under these conditions! This is the largest cornulitid I’ve seen.

Ken_Karns_preparatory_labHere is Ken Karns in his fossil preparation laboratory, which he assembled himself. The box with the armholes is for air-abrading specimens to remove matrix.

Display cases KenThis is one section of the display cases Ken has in his basement museum. Most of the specimens shown here are from the Waldron Shale.

Platyostoma collection displayedA closer view of a display of Platyostoma from the Waldron Shale. Note the many encrusters.

Lizzie Brian KenLizzie Reinthal, Brian Bade and Ken talk about fossil preparation with some Waldron material. The cases are full of curated specimens.

Encrusted crinoid rootsThere are so many treasures in Ken’s collections. I am fascinated by this little slab showing the holdfast of a crinoid with sheet-like bryozoans encrusting it. The bryozoans show that the roots were at least partially exposed at some point.

Thank you again to Brian Bade for arranging this trip, and Ken Karns for being such a fantastic host. We are looking forward to many Waldron projects in the future!


Baumiller, T.K. 2003. Evaluating the interaction between platyceratid gastropods and crinoids: a cost–benefit approach. Palaeogeography, Palaeoclimatology, Palaeoecology 201: 199-209.

Baumiller, T.K. and Gahn, F.J. 2002. Fossil record of parasitism on marine invertebrates with special emphasis on the platyceratid-crinoid interaction. Paleontological Society Papers 8: 195-210.

Brett, C.E., Cramer, B.D., McLaughlin, P.I., Kleffner, M.A., Showers, W.J. and Thomka, J.R. 2012. Revised Telychian–Sheinwoodian (Silurian) stratigraphy of the Laurentian mid-continent: building uniform nomenclature along the Cincinnati Arch. Bulletin of Geosciences 87: 733–753.

Feldman, H.R. 1989. Taphonomic processes in the Waldron Shale, Silurian, southern Indiana. Palaios 4: 144-156.

Gahn, F.J. and Baumiller, T.K. 2006. Using platyceratid gastropod behaviour to test functional morphology. Historical Biology 18: 397-404.

Gahn, F.J., Fabian, A. and Baumiller, T.K. 2003. Additional evidence for the drilling behavior of Paleozoic gastropods. Acta Palaeontologica Polonica 48: 156-156.

Hall, J. 1881. Descriptions of the Species of Fossils Found in the Niagara Group at Waldron, Indiana. In: Indiana Department of Geology and Natural Resources, Eleventh Annual Report, p. 217-345. [PDF of the text downloadable here.]

Liddell, W.D. and Brett, C.E. (1982). Skeletal overgrowths among epizoans from the Silurian (Wenlockian) Waldron Shale. Paleobiology 8: 67-78.

Peters, S.E. and Bork, K.B. 1998. Secondary tiering on crinoids from the Waldron Shale (Silurian: Wenlockian) of Indiana. Journal of Paleontology 72: 887-894.

Sutton, M.D., Briggs, D.E.G., Siveter, D.J. and Siveter, D.J. 2006. Fossilized soft tissues in a Silurian platyceratid gastropod. Proceedings of the Royal Society B: Biological Science 273(1590): 1039-1044.

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

Wooster’s Fossils of the Week: Bioclaustration-boring structures in bryozoans from the Upper Ordovician of the Cincinnati region

February 9th, 2014

Chimneys 149aAnother bioerosion mystery from those fascinating Upper Ordovician rocks around Cincinnati. Above you see a flat, bifoliate trepostome bryozoan (probably Peronopora) with pock holes scattered across its surface. At first you may think, after reading so many blog posts here, that these are again the simple cylindrical boring Trypanites, but then you note that they are shallow and have raised rims so that they look like little meteorite craters. These holes thus represent tiny organisms on the bryozoan surface while it was alive. The bryozoan grew around these infesters, producing the reaction tissue of the rims. This is a kind of preservation called bioclaustration (literally, “walled-in life” from the same root in claustrophobia and cloisters). The specimen is from locality C/W-149 (Liberty Formation near Brookville, Franklin County, Indiana; 39º 28.847′ N, 84º 56.941′ W).
Chimneys 153aThis is another trepostome bryozoan with these rimmed pits. It is from locality C/W-153 (Bull Fork Formation near Maysville, Mason County, Kentucky; 38º 35.111′ N, 083º 42.094′ W). The pits are more numerous and have more pronounced reaction rims.
Chimneys 153bA closer view. One of the interesting questions is whether these pits are also borings. Did they cut down into the bryozoan skeleton at the same time it was growing up around them? We should be able to answer that by making a cross-section through the pits to see what their bases look like. The bryozoan walls should be either cut or entire.
Chimneys 153cThis is an older image I made back in the days of film to show the density of the rimmed pits in the same bryozoan as above. If we assume that the pit-maker was a filter-feeding organism, how did it affect the nutrient intake of the host bryozoan? Maybe the infester had a larger feeding apparatus and took a larger size fraction of the suspended food? (This could be a project where we apply aerosol filtration theory.)  Maybe the bryozoan suffered from a cut in its usual supply of food and had a stunted colony as a result? These are questions my students and I plan to pursue this summer and next year.

It is good to get back to the glorious Cincinnatian!


Ernst, A., Taylor, P.D. and Bohatý, J. 2014. A new Middle Devonian cystoporate bryozoan from Germany containing a
new symbiont bioclaustration. Acta Palaeontologica Polonica 59: 173–183.

Kammer, T.W. 1985. Aerosol filtration theory applied to Mississippian deltaic crinoids. Journal of Paleontology 59: 551-560.

Palmer, T.J. and Wilson, M.A. 1988. Parasitism of Ordovician bryozoans and the origin of pseudoborings. Palaeontology 31: 939-949.

Rubinstein, D.I. and Koehl, M.A.R. 1977. The mechanisms of filter feeding: some theoretical considerations. American Naturalist 111: 981-994.

Tapanila, L. 2005. Palaeoecology and diversity of endosymbionts in Palaeozoic marine invertebrates: trace fossil evidence. Lethaia 38: 89-99.

Taylor, P.D. and Voigt, E. 2006. Symbiont bioclaustrations in Cretaceous cyclostome bryozoans. Courier Forschungsinstitut Senckenberg 257: 131-136.

Wooster’s Fossils of the Week: Mysterious borings in brachiopods from the Upper Ordovician of the Cincinnati region

February 2nd, 2014

Half borings 152a1Above is a well-used brachiopod from the Upper Ordovician of northern Kentucky (C/W-152; Petersburg-Bullittsville Road, Boone County; Bellevue Member of the Grant Lake Formation). It experienced several events on the ancient seafloor during its short time of exposure. Let’s put a few labels on it and discuss:

Half borings 152a2Our main topic will be those strange ditch-like borings (A) cut across into the exterior of this brachiopod shell. This is an example of bioerosion, or the removal of hard substrate (the calcitic shell in this case) by organisms. These structures were likely created by worm-like filter-feeders. The shell also has a nice trepostome bryozoan (B) encrusting it (and partially overlapping the borings) and the heliolitid coral Protaraea richmondensis (C), which is distinguished by tiny star-like corallites. The borings are what we need to make sense of in this tableau. Here’s another set on another brachiopod:

Half borings 152bThis closer view of a brachiopod shell exterior from the same locality shows two of these horizontal borings. The mystery is why we see only half of the boring. These are apparently cylindrical borings of the Trypanites variety, but they should be enclosed on all sides as tubes. Why is half missing? It is as if the roofs have been removed. I think that is just what happened.

Half borings 152cThis encrusted and bored brachiopod, again from the same locality, gives us clues as to what likely happened. Here we see an encrusting bryozoan and those borings together. The borings cut through the bryozoan down into the brachiopod shell. Could it be that encrusting bryozoans provided the other half of the borings?

BoringXsectHere’s a test of that idea. Above is a cross-section through the boundary between an encrusting bryozoan (above) and a brachiopod shell (below). It was made by cutting through the specimen, polishing it, and then making an acetate peel. The bryozoan shows the modular nature of its colonial skeleton, and the brachiopod displays its laminar shell structure. The two round features are sediment-filled borings running perpendicular to the plane of the section. The boring on the left is completely within the brachiopod shell; the one on the right is cut along the interface of the bryozoan and brachioopod. Remove the bryozoan and we would have a half-boring as discussed above.

Half borings 152eIf that postulate is true, it means that the encrusting byozoans must have been removed from the brachiopod shells, taking the other halves of the borings with them. We should thus find bryozoans that “popped” off the shells with the equivalent half-borings on their undersides. You know where this is going. The bryozoan above (same locality) shows its upper surface. Note that there are a scattering of tiny borings punched into it.

Half borings 152fThis is the underside of the bryozoan. We are looking at its flat attachment surface. It was fixed to a shell of some kind (I can’t tell what type) and became detached from it. You see the half-borings along with vertical borings drilled parallel to the attachment surface. It appears that small organisms drilled into the bryozoan zoarium (colonial skeleton) on its upper surface, penetrated down to the boundary with the brachiopod shell, and then turned 90° and excavated along the boundary between brachiopod and bryozoan. This makes sense if they were creating a dwelling tube (Domichnia) that they would want surrounded by shell. Punching straight through the bryozoan and brachiopod would leave them in a tube without a base. What would this look like from the inside of the brachiopod shell?

Half borings 152dThis time we’re looking at the interior of a brachiopod shell (same location) that has been exfoliated (some shell layers have been removed). The horizontal borings are visible running parallel to the shell.

Horizontal in bivalveThis view of an encrusted bivalve shell may help with the concept. In the top half you see an encrusting bryozoan. In the bottom you see bivalve shell exposed where the bryozoan has been broken away. Cutting into that shell are the horizontal borings. Their “roofs” were in the now-missing parts of the bryozoan.

There are two conclusions from this hypothesis: (1) There was a group of borers who drilled to this interface between bryozoan and brachiopod skeleton, detected the difference in skeleton type, and then drilled horizontally to maintain the integrity of their tubes; (2) the bryozoans were cemented to the brachiopods firmly enough that the borers could mine along the interface, but later some bryozoan encrusters were removed, leaving no trace of their attachment save the half-bored brachiopod shell. This latter conclusion is disturbing. A tacit assumption of workers on the sclerobionts (hard-substrate dwellers) of brachiopods and other calcitic skeletons is that the calcitic bryozoans cemented onto them so firmly that they could not be dislodged. We could thus record how many shells are encrusted and not encrusted to derive paleoecological data about exposure time, shell orientations and the like. But if the robust bryozoans could just come off, maybe that data must be treated with more caution? After all, bryozoans that were removed from unbored brachiopods could leave no trace at all of their former residence.

Two students and I presented these ideas at a Geological Society of America meeting eight years ago (Wilson et al., 2006), but we never returned to the questions for a full study. Now a new generation of students and I have started a project on this particular phenomenon of sclerobiology. It will involve collecting more examples and carefully dissecting them to plot out the relationship between the borings and their skeletal substrates. We also want to assess the impact these observations may have on encruster studies. Watch this space a year from now!


Brett, C.E., Smrecak, T., Hubbard, K.P. and Walker, S. 2012. Marine sclerobiofacies: Encrusting and endolithic communities on shells through time and space, p. 129-157. In: Talent, J.A. (ed.), Earth and Life; Springer Netherlands.

Smrecak, T.A. and Brett, C.E. 2008. Discerning patterns in epibiont distribution across a Late Ordovician (Cincinnatian) depth gradient. Geological Society of America Abstracts with Programs 40:18.

Wilson, M.A., Dennison-Budak, C.W. 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 38:514.

Wooster’s Fossils of the Week: Trace fossils making ghostly shells (Upper Cretaceous of Mississippi)

January 26th, 2014

Entobia gastropod Prairie Bluff Chalk FormationThe unusual fossil above was collected by Megan Innis (’11) and myself in Mississippi during a May 2010 paleontological expedition with Caroline Sogot and Paul Taylor of The Natural History Museum, London. That splendid trip has contributed already to one high profile publication (Sogot et al., 2013) and no doubt more will come from the excellent collections we made. All the fossils in this post came from the Prairie Bluff Chalk Formation (Maastrichtian) exposed at the intersection between Highway 25 and Reed Road in Starkville, Mississippi (locality C/W-395).

The specimen is a marine gastropod (fancy name for a snail), which is hard to believe considering no shell is preserved. The shape of the original aragonitic shell has been taken by a series of interlocking blobs, each with a sediment-filled tube extending outwards. These are casts of chambers made by a boring clionaid sponge. The resulting trace fossil is known as Entobia, a form we have seen several times in this blog. The sequence of events: (1) The sponges excavated cavities connected by tunnels into the aragonite shell of the gastropod, maintaining connections to the seawater for filter-feeding; (2) the cavities and tubes filled with fine-grained calcareous sediment after the death of the sponges; (3) the aragonite gastropod shell dissolved away, probably at the same time the sediment filling the cavities was cemented; (4) the fossil was exhumed as a series of natural casts of the sponge cavities — the trace fossil Entobia.
Entobia bivalve 1 exterior Prairie Bluff Chalk FormationThere were many other such fossil ghosts at this locality, such as the apparent bivalve shell fragment above.
Entobia cast close Prairie Bluff Chalk FormationIn this closer view (taken with my new extension tubes on the camera) we see some of the interlocking sponge chamber casts. On the surfaces of some you can just make out a reticulate pattern that represents tiny scoop-like excavations by the sponges. In the upwards-extending tubes there are a few green grains of the marine mineral glauconite.

As a paleontologist it is always sobering to see a fossil preserved in such an odd way. Were it not for these circumstances of boring, filling and cementation, the shells would have completely disappeared from the fossil record. Every fossil we have, really, is a victory of improbable preservation.


Bromley, R.G. 1970. Borings as trace fossils and Entobia cretacea Portlock, as an example. Geological Journal, Special Issue 3: 49–90.

Schönberg, C.H. and Shields, G. 2008. Micro-computed tomography for studies on Entobia: transparent substrate versus modern technology, p. 147-164. In: Current Developments in Bioerosion. Springer; Berlin, Heidelberg.

Sogot, C.E., Harper, E.M. and Taylor, P.D. 2013. Biogeographical and ecological patterns in bryozoans across the Cretaceous-Paleogene boundary: Implications for the phytoplankton collapse hypothesis. Geology 41: 631-634.

Sohl, N.F. 1960. Archeogastropoda, Mesogastropoda, and stratigraphy of the Ripley, Owl Creek, and Prairie Bluff Formations, p. A1-A151. In: Late Cretaceous gastropods in Tennessee and Mississippi: U.S. Geological Survey Professional Paper 331-A.

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. 2007. Macroborings and the evolution of bioerosion, p. 356-367. In: Miller, W. III (ed.), Trace Fossils: Concepts, Problems, Prospects. Elsevier, Amsterdam, 611 pages.

Wooster’s Fossil of the Week: A crinoid-rich Lower Carboniferous siderite concretion (part III — those crinoids had company)

January 19th, 2014

Crinoid with platyceratid (cross-section) 585The last installment of our analysis of a Lower Carboniferous fossiliferous siderite concretion given to the department by Sam Root. In part I we looked at the crinoid stems and calices on the outside and discuss the formation of siderite concretions and the preservation of this particular assemblage. In part II we had our first look at polished sections of the concretion, taking special note of the crinoid stem morphology and its replacement by the mineral marcasite. For part III you were promised a molluscan surprise.

In the top view you can see that we have a section that fortuitously cut right through the center of a crinoid head. The stem is visible at the bottom, with the calyx and attached arms above. Crowning the calyx is a thin semi-circle of shell nestled open-side-down across the crinoid oral surface. This we can tell from the shell morphology is a parasitic platyceratid gastropod caught in place on its crinoid host. Nice.
Platyceratid Lower Carboniferous 585 annotatedThree years ago we received a fossil donation from the Calhoun family of local Lower Carboniferous fossils, including this beauty pictured above. It is a crinoid calyx (you can tell by the polygonal plates) with a cap-shaped platyceratid gastropod (Palaeocapulus acutirostre) preserved in place on top of it between the arms (now missing). I drew a line across the image to indicate the likely plane of section through a similar pair in our siderite concretion. In section the platyceratid would be recorded as a thin shelly top on the calyx.

Platyceratids have long been known as Paleozoic associates of crinoids. For many years we thought of them as simply coprophagous, meaning they were consuming crinoid feces as they exited the anus. (Awkward conversation, I know.) Careful work by Tom Baumiller (1990) showed that this arrangement (which would not have directly harmed the crinoid because it was, after all, done with the food) was likely not the case. He found trace fossil evidence that the platyceratids were likely accessing crinoid stomach contents directly through some sort of proboscis, and that these parasitized crinoids were stunted in their growth and thus directly harmed (but not killed — no good parasite wants to lose its meal ticket). Our new specimen was thus likely a miserable little crinoid, even if it didn’t have a brain to sort out its feelings.
Stem Calyx 121413As one last view of our crinoids in the concretion, look at the detail in the crinoid stem just below the calyx. The lumen is visible in the center of the stem, as well as the alternating ornaments on the columnals.

This has been a fun specimen to examine. Thanks, Sam!


Baumiller, T.K. 1990. Non-predatory drilling of Mississippian crinoids by platyceratid gastropods. Palaeontology 33: 743-748.

Donovan, S.K., and Webster, G.D. 2013. Platyceratid gastropod infestations of Neoplatycrinus Wanner (Crinoidea) from the Permian of West Timor: speculations on thecal modifications. Proceedings of the Geologists’ Association 124: 988–993.

Wooster’s Fossil of the Week: A crinoid-rich Lower Carboniferous siderite concretion (part II — the inside story)

January 12th, 2014


1 Cross-section macro 2 121413Last week’s specimen was a Lower Carboniferous fossiliferous siderite concretion from an unknown location, but likely from the Wooster area. It was donated to the department by Emeritus Geology Professor Sam Root. The concretion has beautiful crinoids preserved in it, including several stems of at least two types and three calices (crowns or heads).

I took a chance and cut the concretion with a rock saw if there were interesting features on the inside. There were indeed! In the image above you see at the bottom a cross section through a broken crinoid stem showing the articulated columnals. Above it are sections of crinoid arms (the white and grey spots) each trailing a pair of delicate pinnules (the feeding parts of the arms that carried tube feet). The arms are coming from an intact calyx that is not in the plane of the section.
2 Micro 1 121413In this closer view of the above stem we see the complex anatomy of the crinoid stem. We also see the amazing mineralogy of these specimens in a way we could not from the outside. The light brown matrix is, as we’ve said, the concretion made primarily of siderite (an iron carbonate) and clay. The crinoid columnals, which were originally made of calcite (calcium carbonate), have a silvery metallic material replacing them. This is the iron sulfide mineral marcasite. The white mineral on the inside of the stem on the left is quartz (silicon dioxide). It filled in open spaces inside the stem. To confuse things (nothing is ever easy in this business!) on the right end of the stem marcasite has filled in the cavities instead of quartz.
3 Macro close 121413This view of another stem in cross-section shows a fourth mineral in the system: calcium carbonate. It can be seen as the glassy material in the middle of the structure. It is not the original calcite that made up the columnals. It is instead a later mineral that, like the quartz and marcasite in the previous image, filled in open spaces within the stem. The marcasite, quartz and calcite are thus secondary minerals introduced to the fossil long after its burial. We call these chemical and physical changes to the original mineralogy diagenesis.
4 Fearnhead 2008 Fig 2Since this cross-section view of the crinoid stems is surprisingly complicated, here is a diagram from Fearnhead (2008, figure 2). The top is a crinoid columnal looking at its articulating surface. At the bottom is a cross-section. In our crinoids you can easily make out the lumen as a hollow space running through the center of the stems (filled with marcasite, calcite or quartz). The zygum is that portion of the columnal replaced by marcasite.

Lat week I mentioned that there was a molluscan surprise revealed upon cutting open this concretion. I’ll save that for part III of this series. Same channel next week!


Fearnhead, F.E. 2008. Towards a systematic standard approach to describing fossil crinoids, illustrated by the redescription of a Scottish Silurian Pisocrinus de Koninck. Scripta Geologica 136: 39-61.

Wooster’s Fossil of the Week: A crinoid-rich Lower Carboniferous siderite concretion (part I)

January 5th, 2014

Cobble Top 121413Last year Wooster emeritus geology professor Sam Root generously donated the above pictured siderite concretion to our paleontology collections. He had received it from a friend who didn’t know where it came from originally so we have no location. The fossils in it, though, show it is Lower Carboniferous in age and could well be from local outcrops of the Cuyahoga Formation. Sam knew this is a cool specimen so he wanted to see what we could make of it.

In the top view we can see crinoid stems running transversely across the surface. Remarkably, two crinoid calices (the arm-bearing crown of the crinoid at the top of the stem) are visible. The larger one is in the lower left. You can see the top of the stem to the farthest left, and then the calyx and attached arms to the right. The second calyx is in the upper right with the arms extending down and towards us. Finding one crinoid calyx with the delicate arms still attached is impressive; finding two in the same slab is a real treat.
Siderite Concretion Carboniferous 585Above is the other side of the concretion. Again a crinoid stem can be seen transverse across the surface. This stem is different from those on the other side, though. It does not have external sculpture, and it is separated into distinct pluricolumnals as if someone sawed through it at regular intervals.
Cobble closer 121413A closer view of the above shows yet another crinoid calyx, this one almost entirely buried in the rock with the arms extending to the surface. The arms have smaller sub-arms (pinnules) still attached. Amazing.

The concretion is made of the mineral siderite (an iron carbonate) that precipitated in fine-grained sediments around the fossils after they were buried. This usually takes place under subsurface anoxic and slightly acidic conditions. The crinoids with all their small and easily-disarticulated parts were buried quickly on the ancient seafloor, probably by a storm-induced pulse of silts and clays. The decay of their soft parts produced hydrogen sulfide gas ad carbon dioxide, triggering the geochemistry that caused the precipitation of siderite around them. The hard concretion that resulted was likely in a matrix of soft shale. The strength of the siderite kept the fossils from being crushed by the weight of sediment above. At some point many millions of years later, the shale eroded away and the concretion was freed to be picked up by some lucky person.

The crinoid stem that is divided into regular increments is interesting on its own. These segments with multiple columnals (the poker chip-like individual elements) are called pluricolumnals. They likely broke at pre-set weaknesses in the connective tissue of the living crinoid, something we see in their living descendants. This may have allowed them to break off their stems (autotomize) when in danger so that the calyx and remaining stem could float away for re-establishment elsewhere.

This concretion is so interesting that I (forgive me, Sam) could not resist cutting it open to see what is inside. The inner view is even more fascinating and will be revealed next week in part II of this story. As a teaser, it involves four minerals and a surprising mollusk!


Baumiller, T.K. and Ausich, W.I. 1992. The broken-stick model as a null hypothesis for crinoid stalk taphonomy and as a guide to the distribution of connective tissue in fossils. Paleobiology 18: 288-298.

Gautier, D.L. 1982. Siderite concretions; indicators of early diagenesis in the Gammon Shale (Cretaceous). Journal of Sedimentary Research 52: 859-871.

Wooster’s Fossil of the Week: Glyptodon carapace fragment from the Pleistocene

December 29th, 2013

Glyptodon carapace fragment Pleistocene 585This is a tiny bit of a large and fascinating Pleistocene animal from Central and South America. It is Glyptodon, an impressively large mammal with bony armor much like its cousin the armadillo. The above fossil is a fragment of that carapace. Each roundel is called a scute.
Glyptodon carapace side 585This is a side view of the above carapace fragment showing its thickness and layered, bony nature.
Glyptodon ReconstructionThis modern reconstruction of Glyptodon (from Wikipedia with a GNU free documentation license) shows its primary features, including the bony shell (the size and shape of a Volkswagen Beatle, as is often stated) and its characteristically large claws. It belongs to the Superorder Xenarthra, which includes armadillos, sloths and anteaters. I see the resemblance. They could not completely go turtle, as it were, but it could pull its head back enough into the shell that the scutes on the top of the skull would protect it like a cap. They had massive jaws and flat grinding teeth typical of a large herbivore. Its squat skeleton had a variety of features to support the heavy shell, including fused vertebrae and elephant-like short, stout limbs. They went extinct only about 10,000 years ago, possibly having been hunted to oblivion by early Americans. There is even some evidence that people used their empty shells as shelters.
Richard_OwenGlyptodon was formally named as a genus in 1839 by the extraordinary Sir Richard Owen (1804-1892). Owen was a giant of natural history through most of the 19th Century. He is most remembered for inventing the term Dinosauria (“terrible lizards”) and for being on the wrong side of history at the beginning of the Darwinian Revolution. He was apparently ambitious to the point of severity, and very tough on his contemporary scientists. Thomas Henry Huxley, for example, despised Owen for his treatment of his colleagues. Ironically, Huxley did considerable work on further describing Glyptodon in 1865. Owen had vision as well as sharp observational skills. He was a primary force in the eventual establishment of the Natural History Museum in London in 1881. It can be argued that this museum set the high standards of accessibility and research we now expect from all such institutions. Sir Richard Owen is such a large and well known figure I can simply refer you to one of many websites describing Owen’s life and contributions.

This post marks three complete years of Wooster’s Fossil of the Week. That’s 156 posts. You can visit the very first post (about a Devonian tabulate coral) and see how the entries have evolved, so to speak. We still have plenty more fossils to describe!


Gallo, V., Avilla, L.S., Pereira, R.C. and Absolon, B.A. 2013. Distributional patterns of herbivore megamammals during the Late Pleistocene of South America. Anais da Academia Brasileira de Ciências 85(2): 533-546.

Huxley, T.H. 1865. On the osteology of the genus Glyptodon. Philosophical Transactions of the Royal Society of London 155: 31-70.

Oliveira, É.V., Porpino, K.O. and Barreto, A.F. 2010. On the presence of Glyptotherium in the Late Pleistocene of northeastern Brazil, and the status of “Glyptodon” and “Chlamydotherium“. Paleobiogeographic implications. Neues Jahrbuch für Geologie und Paläontologie-Abhandlungen 258(3): 353-363.

Owen, R. 1839. Description of a tooth and part of the skeleton of the Glyptodon, a large quadruped of the edentate order, to which belongs the tessellated bony armor figured by Mr. Clift in his memoir on the remains of the Megatherium, brought to England by Sir Woodbine Parish. FGS Proceedings of the Geological Society of London 3: 108-113.

Wooster’s Fossils of the Week: Rugose corals from the Upper Ordovician of Ohio

December 22nd, 2013

585px-LibertyFormationSlab092313College of Wooster student Willy Nelson spotted and collected up this beautiful Liberty Formation slab on our 2013 Invertebrate Paleontology course field trip to the Upper Ordovician of the Caesar Creek area in southern Ohio. There are many exquisite fossils on this apparent carbonate hardground (a cemented seafloor), the most prominent of which are the four linked circular corallites in the top center. They are of the species Streptelasma divaricans (Nicholson, 1875), shown in more detail below.

Streptelasma divaricans (Nicholson, 1875) 585Streptelasma divaricans is a rugose coral, a prominent order that dominated the Paleozoic coral world from the Ordovician into the Permian. Unlike most rugose corals, it usually is found attached to some hard surface like a shell, rock or hardground. S. divaricans is relatively rare in the Upper Ordovician of the Cincinnati area compared to its free-living cousin Grewingkia canadensis. In its adult form (as seen here) it can have about 60 septa (vertical partitions radiating from the center), alternating from small to large and often with a twist at the center. In life there would have been a tentacle-bearing polyp sitting in each of these septate cups (corallites) catching tiny prey as it passed by in the water currents. We presume that they lived much like modern corals today. S. divaricans was, by the way, an invading species in this Late Ordovician shallow sea community.

Streptelasma divaricans was named as Palaeophyllum divaricans in 1875 by Henry Alleyne Nicholson (1844-1899). We met Dr. Nicholson in an earlier blogpost. Astonishingly, one of our  geology majors in the paleontology course this semester is Brittany Nicholson, a direct descendant. Way cool.
WillyBrachiopodLepidocyclusperlamellosus092313Another nice fossil on Willy’s slab (in the upper right) is the rhynchonellid brachiopod Lepidocyclus perlamellosus, shown closer above.
WillyBivalve092313The curved, indented line in the middle of the slab (shown above) appears to be the outline of a bivalve shell. The original shell was made of aragonite and thus dissolved away very early (possibly even on the seafloor before burial). There is not enough shape remaining to identify it. The twig-like fossil with tiny holes above the scale is, of course, a trepostome bryozoan. You didn’t need me to tell you that!


Elias, R.J. 1983. Middle and Upper Ordovician solitary rugose corals of the Cincinnati Arch region. United States Geological Survey Professional Paper 1066-N: 1-13.

Elias, R.J. 1989. Extinctions and origins of solitary rugose corals, latest Ordovician to earliest Silurian in North America. Fossil Cnidaria 5: 319-326.

Nicholson, H.A. 1875. Description of the corals of the Silurian and Devonian systems. Ohio Geological Survey Report, v. 2, part 2, p. 181-242.

Patzkowsky, M.E. and Holland, S.M. 2007. Diversity partitioning of a Late Ordovician marine biotic invasion: controls on diversity in regional ecosystems. Paleobiology 33: 295-309.

Wooster’s Fossil of the Week: A trepostome bryozoan from the Upper Ordovician of northern Kentucky

December 15th, 2013

Heterotrypa Corryville 585First, what U.S. state does this delicious little bryozoan resemble? It’s so close I can even pick out Green Bay. This is Heterotrypa frondosa (d’Orbigny, 1850), a trepostome bryozoan from the Corryville Formation (Upper Ordovician) in Covington, Kentucky. I collected it decades ago while exploring field trip sites for future classes. This zoarium (the name for a bryozoan colony’s skeleton) is flattened like a double-sided leaf, hence the specific name referring to a frond. In the view above you can see a series of evenly spaced bumps across the surface termed monticules. A closer view is below.
Heterotrypa closer 585The monticules are composed of zooecia (the skeletal tubes for the individual bryozoan zooids) with slightly thickened walls standing up above the background of regular zooecia. The hypothesized function of these monticules was to make the filter-feeding of the colony more efficient by utilizing passive flow to produce currents and whisk away excurrents from the lophophores (feeding tentacles) like little chimneys. In 1850, Alcide Charles Victor Marie Dessalines d’Orbigny (French, of course) originally named this species Monticulipora frondosa because of the characteristic bumps.
Boring in Heterotrypa 585If you look closely at the zoarium you will see holes cut into it that are larger than the zooecia. A closer view of one is shown above. These are borings called Trypanites, which have appeared in this blog many times. They were cut by some worm-like organism, possibly a filter-feeding polychaete, that was taking advantage of the bryozoan skeleton to make its own home. It would have extended some sort of filtering apparatus outside of the hole and captured organic particles flowing by. It was a parasite in the sense that it is taking up real estate in the bryozoan skeleton that would have been occupied by feeding zooids. It may not have been feeding on the same organic material, though, as the bryozoan. It may have been consuming a larger size fraction than the bryozoan zooids could handle.


Boardman, R.S. and Utgaard, J. 1966. A revision of the Ordovician bryozoan genera Monticulipora, Peronopora, Heterotrypa, and Dekayia. Journal of Paleontology 40: 1082-1108

d’Orbigny, A. D. 1850. Prodro/ne de Paleontologie stratigraphique universelle des animaux mollusques & rayonnes faisant suite au cours elementaire de Paleontologie et de Geologic stratigraphiques, vol. 2. 427 pp. Masson, Paris.

Erickson, J.M. and Waugh, D.A. 2002. Colony morphologies and missed opportunities during the Cincinnatian (Late Ordovician) bryozoan radiation: examples from Heterotrypa frondosa and Monticulipora mammulata. Proceedings of the 12th International Conference of the International Bryozoology Association. Swets and Zeitlinger, Lisse; pp. 101-107..

Kobluk, D.R. and Nemcsok, S. 1982. The macroboring ichnofossil Trypanites in colonies of the Middle Ordovician bryozoan Prasopora: Population behaviour and reaction to environmental influences. Canadian Journal of Earth Sciences 19: 679-688.

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