Wooster’s Fossil of the Week: A receptaculitid (Middle Ordovician of Missouri)

February 10th, 2017

This week’s fossil is a long-standing paleontological mystery. Above is a receptaculitid from the Kimmswick Limestone (Middle Ordovician) near Ozora, Missouri. I think I found it on a field trip with Frank Koucky in the distant mists of my student days at Wooster, but so many outcrops, so many fossils …

Below is a nineteenth century illustration of a typical receptaculitid fossil. They are sometimes called “sunflower corals” because they look a bit like the swirl of seeds in the center of a sunflower. They were certainly not corals, though, or probably any other kind of animal. Receptaculitids appeared in the Ordovician and went extinct in the Permian, so they were confined to the Paleozoic Era. Receptaculitids were bag-like in form with the outside made of mineralized pillars (meroms) with square or diamond-shaped heads. The fossils are usually flattened disks because they were compressed by burial. You may notice now that the fossil at the top of this post is a mold of the original with the dissolved pillars represented by open holes. (Paleontologists can argue if this is an external or internal mold.)So what were the receptaculitids? When I was a student we called them a kind of sponge, something like a successor of the Cambrian archaeocyathids. In the 1980s a convincing case was made that they were instead a kind of alga of the Dasycladales. Now the most popular answer is that they belong to that fascinating group “Problematica”, meaning we have no idea what they were! (Nitecki et al., 1999). It’s those odd meroms that are the problem — they appear in no other known group, fossil or recent.

I find it deeply comforting that we still have plenty of fossils in the Problematica. We will always have mysteries to puzzle over.
Another Wooster receptaculitid specimen, this time seen from the underside showing side-views of the meroms.
Diagram of a receptaculitid in roughly life position showing its inflated nature and pillar-like meroms. From Dawson (1880, fig. 25): a, Aperture (probably imaginary here). b, Inner wall. c, Outer wall. n, Nucleus, or primary chamber. v, Internal cavity.

Finally, this is what a typical receptaculitid looks like in the field (Ordovician of Estonia). Note that nice sunflower spiral of the merom ends.


Dawson, J.W. 1880. The chain of life in geological time: A sketch of the origin and succession of animals and plants. The Religious Tract Society, 272 pages.

Nitecki, M.H., Mutvei, H. and Nitecki, D.V. 1999. Receptaculitids: A Phylogenetic Debate on a Problematic Fossil Taxon. Kluwer Academic/Plenum, 241 pages.

[Originally published on September 18, 2011]

Wooster’s Fossils of the Week: Revisiting a pair of hyoliths from the Middle Ordovician of Estonia

January 20th, 2017

We met these modest internal molds of the mysterious hyoliths about five years ago. With a dramatic new development in hyolith studies, they are worth seeing again.

These fossils are internal molds (the sediment that filled the shell) of of flattened cones composed of the carbonate mineral aragonite. The aragonite shells dissolved away after burial, leaving the cemented sediment behind. That’s what we see above, in their stark simplicity. (We also see wiggly indentations that are the trace fossil Arachnostega, which is what I collected them for in the first place.) They were found in the Middle Ordovician of Estonia.

Hyalites, though common throughout the Paleozoic, have been difficult to place in a taxonomic category. Because of their easily-dissolved aragonite skeletons, most fossils are like these — simple molds and casts. A few were found with some preserved internal organs, which added to the intrigue. Their flattened conical shells had a hinged lid (operculum) over the open end. Extending from each side in the space between the operculum and cone were two calcareous rods called helens (a name deliberately chosen so as not to evoke a particular function). They were rumored to be deposit-feeders, based on no real evidence, it turns out.

An excellent paper appeared earlier this month showing dramatic evidence of hyolith soft parts in the Cambrian of western Canada (Moysiuk et al., 2017). The authors reconstruct the iconic Cambrian hyolith Haplophrentis “as a semi-sessile, epibenthic suspension feeder that could use its helens to elevate its tubular body above the sea floor”. Their primary evidence is a magnificently preserved lophophore (tentacular filter-feeding apparatus) and a U-shaped digestive tract with a dorsolateral anus. These features not only give the hyoliths a life mode and feeding habit, they place them systematically among the lophophorates, a group that includes brachiopods, phoronids and bryozoans.

Haplophrentis in the Burgess Shale (Middle Cambrian) at the Walcott Quarry, Burgess Pass, British Columbia, Canada.

Reconstruction of Haplophrentis on the Cambrian sea floor. The tentacular lophophore is seen extending out underneath the operculum. Beautiful art by D. Dufault of the Royal Ontario Museum.

It’s not often we see such dramatic changes in the taxonomic placement and paleoecological habits of a large, extinct group. It is also not often that invertebrate fossils make headlines!


Moysiuk, J., Smith, M.R. and Caron, J.B. 2017. Hyoliths are Palaeozoic lophophorates. Nature doi:10.1038/nature20804

Wooster’s Fossils of the Week: Upper Ordovician brachiopods and bryozoans from paleontology class collections

January 6th, 2017

1-geopetal-tommyLast semester the Invertebrate Paleontology class at Wooster had its annual field trip into the Upper Ordovician of southern Ohio. We had a great, if a bit muddy, time collecting fossils for each student’s semester-long project preparing, identifying, and interpreting their specimens. Like all research, especially when it starts in the field, there were discoveries and surprises. I always highlight a particular specimen collecting by a student in this blog.

Above is a cross-section of a specimen found by Tommy Peterson (’19). It is the rhynchonellid brachiopod Hiscobeccus capax almost completely enveloped by an encrusting trepostome bryozoan. We’ve cut through the center of the brachiopod, revealing gray micritic sediment and clear calcite crystals. We can infer from this simple specimen that the brachiopod died and its shell remained articulated. Sediment drifted in, filling the bottom half of the shell. The bryozoan eventually sealed it all up as it used the brachiopod shell for a hard substrate on a muddy seafloor. The remaining void space was filled in by the precipitation of calcite crystals. You can see that the crystals nucleated from the outer margin of the cavity and grew inwards, a kind of calcareous geode. I’m intrigued by the irregular sediment surface and the manner in which calcite nucleated upwards from it. I suspect this sediment was itself cemented before the calcite crystals appeared.

This kind of structure is called a geopetal. It shows the “way up” at the time of crystal formation. Gravity held the pocket of sediment in the bottom of the shell, leaving the void at the top. Nice little specimen.

2-constellaria-alexisThis star-studded bryozoan found by Alexis Lanier (’20) was going to be the Fossil of the Week, but then I saw that last year I highlighted the very same species! I think the bryozoan Constellaria is cool. Read all about it and its history at the link.

3-table-of-traysHere are the completed specimen trays for half the class. (Grading this project took, as you might imagine, considerable time!). Every week in lab, after we had done the assigned work, we got out the trays and cleaned, prepared, and identified the specimens. Students learned how to use the rock saws and make acetate peels of the bryozoans and corals.

4-tray-insideInside a typical tray. We are very grateful for the many online sources to aid identification of these Cincinnatian fossils. Three in particular were most valuable: Alycia Stigall’s Digital Atlas of Ordovician Life, Steve Holland’s stratigraphic and paleontological guide to the Cincinnatian, and the spectacular Dry Dredgers website.

Ohio is a paleontological paradise!

Wooster’s Fossils of the Week: Ordovician bioerosion trace fossils

December 9th, 2016

screen-shot-2016-12-03-at-2-06-03-pmThis week’s post is a celebration of the appearance of a remarkable two-volume work on trace fossils and evolution. The editors and major authors are my friends Gabriela Mángano and Luis Buatois (University of Saskatchewan). They are extraordinary geologists, paleontologists and ichnologists (specialists on trace fossils). They led this massive effort of multiple authors and thousands of manuscript pages. Turns out they are inspiring scientific leaders as well as sharp-eyed editors.

My contribution is in the first volume within a chapter (co-authored with Gabriela, Luis, and Mary Droser of the University of California, Riverside) entitled “The Great Ordovician Biodiversification event”. We examine here the relationship between trace fossils and the critical evolution of marine communities through the Ordovician. My main responsibility was sorting out the changes in the bioeroders over the course of the period. Way back in 2001, Tim Palmer and I noticed a rise in bioerosion trace fossil diversity and abundance in the Middle and Late Ordovician. We grandly called it the “Ordovician Bioerosion Revolution”. The concept and name stuck.

The top image is Fig. 4.8 from the book. The caption: Upper Ordovician bioerosion structures. (a) Trypanites weisi (cross-sectional view) in a carbonate hardground. Katian, Grant Lake Limestone, near Washington, Kentucky, USA; (b) Trypanites weisi (bedding-plane view) in a carbonate hardground. Katian, Grant Lake Limestone, near Manchester, Ohio, USA; (c) Palaeosabella isp. in a trepostome bryozoan. Katian, Whitewater Formation, near Richmond, Indiana, USA; (d) Petroxestes pera. Katian, Whitewater Formation, Caesar Creek Lake emergency spillway, near Waynesville, Ohio, USA; (e) Ropalonaria venosa in a strophomenid brachiopod. Katian, Liberty Formation near Brookville, Indiana, USA.

screen-shot-2016-12-03-at-2-08-42-pmThe cover of the book, which is described here on the publisher’s website.


Mángano, G., Buatois, L., Wilson, M.A. and Droser, M. 2016. The Great Ordovician Biodiversification event, p. 127-156. In: Mángano, G. and Buatois, L. (eds.), The trace-fossil record of major evolutionary events. Topics in Geobiology 39 (Springer).

Wilson, M..A. and Palmer, T.J. 2001. The Ordovician Bioerosion Revolution. Geological Society of America Annual Meeting, Boston, Paper No. 104-0. November 7, 2001.

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

Wooster’s Pseudofossils of the Week: Artifacts in thin-sections of Ordovician limestones from southeastern Minnesota

October 21st, 2016

1bubfirstIt is always exciting to a geologist when thin-sections of curious rocks are completed and ready for view. A thin-section is a wafer of rock (30 microns thick) glues to a glass slide and examined by transmitted light through a petrographic microscope. They provide fantastic views of the mineralogy, paleontology, and structure of a rock in exquisite detail. Thin-sections are also full of mysteries since we have essentially two-dimensional slices through three-dimensional materials.

Thin-sections from the Decorah Formation samples collecting by Team Minnesota this past summer were finally available this week for study. I took the first look at slides of limestones containing ferruginous (iron-rich) ooids we gathered as part of Etienne Fang’s (’17) Independent Study. The first structures I saw were the crazy dark outlines above. What sort of fossils are these, I wondered. Could they be sponges? Odd bryozoans? Borings through the rock fabric? I was ready to post them here as mystery fossils to solicit your opinions. Now, though, they instead make a cautionary tale.

2bub730There are many of these features in a single slide from the Decorah Formation exposed at the Golden Hill outcrop near Rochester, Minnesota. Some are astonishingly complex. It then began to occur to me that these structures were too convoluted and unpredictable to actually be fossils. It also bothered me that to focus on them required to put the rest of the field out of focus. That only made sense if these oddities were in the epoxy, not the rock itself.

3buboverlapEtienne showed me how to demonstrate that these funny loops were not in the rock with this view: You can just make out the greenish lines overlapping the cut surface of this ferruginous ooid. Turns out I was excited about air bubbles in the cementing epoxy. They have nothing to do with the rock. I nearly posted my own pseudofossils.

4trio7321I held out hope, though, that these odd white objects in another thin-section of ooid-rich limestone. They appear to be ghostly outlines of ooids with a finely-textured object inside. They look like seeds with embryos within. Several are scattered through the thin-section. Another mystery fossil!

5duo7321A closer view. Strange how each internal object seems connected to an ooid on the outside, making them asymmetrical in their placements.

6single7321Strange also how once again the details of the internal object can only be seen with the rest of the slide out of focus. Yes, another artifact in the epoxy. This time we may be looking at holes left by ferruginous ooids plucked from the rock through the grinding process, pulling a patch of epoxy with them. Somehow this happened when the now-missing ooid was wedged against another. Nothing to see here, folks.

7ooid7301fAt least I can take the opportunity to show how cool Etienne’s ferruginous ooids are. Note that this one has a greenish layer midway through the cortex. It looks like the mineral chamosite to me. Spectacular detail in the lamellae, but only visible if the image is over-exposed.

8bifoliate7301hThere are plenty of real fossils in these thin-sections, of course. My favorites are these bifoliate bryozoans (lower right half) with their zooecia filled with ferruginous material. Note that the ooid above has had some of its lamellae dissolved away, probably because of some mineral diversity. Also note in the upper right another one of those crazy air bubbles.

The lesson I learn over and over: think, but then think again.




Wooster’s Fossils of the Week: Upper Ordovician strophomenid brachiopods from Iowa

October 7th, 2016

leptaena-585Since we are covering brachiopods in my paleontology course this week, I’ve chosen a very recognizable genus from the Upper Ordovician of Iowa for our Fossil of the Week. This wrinkly strophomenid brachiopod is of the genus Leptaena Dalman, 1828. It is one of the most common brachiopods in the Lower Paleozoic, ranging from the Ordovician into the Carboniferous. The two specimens above are showing their dorsal valve exteriors.

leptaena-dorsal-585The same specimens are here turned over, showing the ventral valve exterior on the left and the dorsal valve interior on the right.

I always learn something when writing these brief fossil posts. These specimens are labeled in our collections as Leptaena rhomboidalis (Wahlenberg, 1818), the most common species name I’ve seen for this genus. Hoel (2005, p. 266), however, says: “In fact, L. rhomboidalis is known only from Gotland, [Sweden,] where it was confined to moderate energy reef environments during the early Wenlockian [Silurian].” So this species is only Silurian, and only found on a Swedish island. I’ll just leave it in open nomenclature, then, as Leptaena sp. The taxonomic details of the many species in the genus are beyond my skills and experience.
gwahlenbergThe erroneous species name, though, does introduce us to a fascinating Swedish naturalist named Göran Wahlenberg (1780-1851). This man is best known as a botanist, but he also had many geological and paleontological interests. He entered Uppsala University in 1792, earning a doctorate in medicine in 1806, and then joining the faculty to teach botany and medicine (with much more emphasis on the first). He occupied the university chair previously held by the demigod taxonomist Carl Linnaeus. He was elected at a young age to the Royal Swedish Academy in 1808. Wahlenberg’s primary work was with plant biogeography, especially in Sweden, but he made many scientific forays throughout Scandinavia and into Central Europe. He named Anomites rhomboidalis in 1818, which was later added to the genus Leptaena.

Wahlenberg studied glaciers in Scandinavia, making many observations about glacial striations and moraines we would recognize today. His main overarching theory of Earth history was that massive vulcanism in the “pre-Adamite” past caused great climate changes, eventually producing a global flood, the evidence for which included glacial erratics strewn throughout northern Europe. He was one of the first naturalists to posit connections between atmospheric composition and global temperatures.

What the scientific biographies of Göran Wahlenberg don’t often mention is that he is credited as the first person to bring the pseudoscience of homeopathy to Sweden. He studied the medicinal ideas of the founder of homeopathy, Samuel Hahnemann, and declared they had merit. He was an enthusiastic advocate, making him one of the “pioneers of homeopathy”. In his defense, at that time homeopathy was no doubt safer than mainline medicine!


Hoel, O.A. 2005. Silurian Leptaeninae (Brachiopoda) from Gotland, Sweden. Paläontologische Zeitschrift 79: 263-284.

Kelly, F.B. 1967. Silurian leptaenids (Brachiopoda). Palaeontology 10: 590-602.

Wahlenberg, G., 1818. Geologisk avhandling om svenska jordens bildning. Uppsala.

Wooster’s Fossils of the Week: Ordovician cryptostome bryozoans from southern Ohio

September 23rd, 2016

waynesville-cryptostomesA short entry this week because the annual meetings of the Geological Society of America and Paleontological Society begin this weekend in Denver. (Wooster is sending 17 students this year. Seventeen! A record for us.)

The above image is a detail from a slab of limestone collected from the Waynesville Formation (Upper Ordovician, Katian) on a class field trip earlier this month to Caesar Creek, Warren County, Ohio.  The stick-like fossils are mostly cryptostome bryozoans generally aligned by the last of some ancient water current. Cryptostomes are small and fussy  bryozoans, and thus hard to work with. There hasn’t been a significant overview of Ohio Ordovician cryptostomes for quite awhile, so I suspect there is much new to learn about them.

The following posts will be from Denver!

2016 Wooster Paleontologists Field Trip

September 11th, 2016

paleo-class-2016-smallIt was a beautiful day for fieldwork. Every fall I take Wooster’s Invertebrate Paleontology class into the field to collect specimens for study and analysis during the rest of the semester. It’s fun because these students have only completed two weeks of the course and almost everything is new. One steady change over the years has been in the number of paleo students. Gone are the days when we could all pile into a 15-passenger van and spend three days in Kentucky. Now we have to take a bus, and tight student schedules limit us to one day. These constraints mean that going to Caesar Creek Lake in Warren County, Ohio, is the best choice. We’ve been here now several times. here we examine Ordovician fossils in limestones and shales of the Waynesville, Liberty and Whitewater Formations (all of which equal the Bull Fork Formation).

collecting-091116The weather was ideal, but the night before saw heavy rains. Bit of a mud fest today. Here we’re at our main collecting site in the Waynesville at the lakeshore (39.482788°N, 84.052376°W).

brach-slab-091116The fossils, of course, are world-class in the Cincinnati area. Here’s a wonderful slab of strophomenid brachiopods with Josh Charlton’s hand for scale. At least the rains washed the rocks clean!

lab-sink-091116Next stop for the students: washing their specimens in the lab sink at Wooster. Anyone who has worked in the Cincinnatian knows that the clay can be particularly tenacious. Students learn paleo from the very basics!


Wooster’s Fossils of the Week: Trepostome bryozoans, burrow systems, and bedding features in an Upper Ordovician limestone from southeastern Minnesota

August 12th, 2016

1 DSC_1322One of the little mysteries on the recent Minnesota research trip by Wooster students, faculty and staff is the origin of thin limestone beds in the middle of the thick shales of the Decorah Formation (Upper Ordovician). How did such accumulations of almost pure carbonate develop on such a muddy seafloor? Are they storm beds? Some sort of diagenetic feature? The records of brief sealevel changes? Brief interruptions in the supply of silicate sediments to the basin? Turbidites of carbonate material swept into a deeper basin? Above is a view of the top surface of such a limestone bed, this one found in the middle of the Decorah in Shop Quarry (N 43.97232°, W 92.38332°). The light-colored twiggy objects are broken colonies of trepostome bryozoans; the network of holes are burrows of a trace fossil called Chondrites.

3 Wangs carbonate bedAn outcrop view of one of these carbonate beds in the Decorah Formation, this one at Wangs Corner (N 44.41047°, W 92.98338°). These units are only a few centimeters thick, and have a variety of petrographic fabrics. This one appears to be an almost pure biosparite with Thalassinoides burrows penetrating from above carrying down a light brown sediment.

2 DSC_1325Back to our slab from the Decorah at Shop Quarry with a closer view of the trepostome bryozoans and round holes representing the trace fossil Chondrites.

3 DSC_1333Sawing a rock and then polishing a cut surface is always fun and profitable! This is a cross-section through the Shop Quarry slab, oriented with the top upwards. A little bit of iron oxide diffused through the sediments provides the touches of red in the fabric of the limestone.

4 DSC_1341This closer view of the cut surface shows the exquisite bedding features, along with the bryozoans (B) and trace fossils (T) in cross-section. The burrows pass through the bedding and pie down into the rock a brownish sediment from above. These burrows were made by some sort of deposit-feeding organism that was mining the sediment for organic material. The bedded sediment may be slightly graded in grain size, meaning the many beds may consist of thin fining-upwards sequences. Note how the beds are contorted around the bryozoans as if they were dropped into the sediment while it was still accumulating.

This slab of bryozoans, trace fossils and contorted laminae looks to me like a storm bed formed quickly during and after the seafloor was significantly disturbed by currents. When conditions returned to normal some worm-like deposit-feeders in the fine sediment above sent their mining tunnels down deep into the carbonate looking for food. We have a hypothesis to test!

A wet cave and the Mighty Mississippi River

August 1st, 2016

1 Niagara Cave 1Rochester, Minnesota — Since Team Minnesota efficiently finished its fieldwork yesterday, we have two days before the students fly out of the Minneapolis-St. Paul airport. The good weather has given us a gift of time, so we’re using it like enthusiastic geologists.

This morning we drove down to Harmony, Minnesota, near the Iowa border to visit Niagara Cave. This cave is unusual because it has a stream with a 60-foot waterfall and (a new term to me) active vadose canyons. The cave is entered down a sinkhole into the Dubuque Formation, and then it descends through the Stewartville Formation and reaches its lowest level in the Prosser Formation. These are Ordovician units above the Platteville-Decorah-Cummingsville sequence we did our work with. The cave passages follow joint patterns inn these limestones. It is plenty wet down there.

2 Cave joint NiagaraMy cave photos are not the best with my small flash. Here at least we can see a vertical joint passage and flowstone structures.

3 Cave StreamThe fast-moving stream running through Niagara Cave.

4 Waterfall top Niagara CaveThe top of the 60-foot waterfall.

5 Cave stratThis view up into a dome shows the internal stratigraphy visible in the limestones.

6 Ceiling gastropodsPlenty of fossils are exposed in the cave. These are sections of gastropods in the ceiling of one section. They were high up so I have little idea of their sizes. I’m just amazed the photo worked out.

7 Queens BluffIn the afternoon we drove northeast to Great River Bluffs State Park on the Mississippi. We had spectacular views of the river and its opposite bank in Wisconsin. Above is a view eastward of Queen’s Bluff overlooking the river.

8 Black River DeltaThe main navigation channel of the Mississippi is in the foreground, with the Black River Delta in the middle ground. In the distance are the bluffs on the Wisconsin side, about 4-5 miles away.

9 Team Minnesota 080116Team Minnesota is ready to answer any geological questions!


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