Wooster Geologists

Mark Wilson March 10th, 2013

Wooster geologists have again greatly benefited from the donation of a collection by an alumnus. George Chambers (’79), a successful professional photographer, sent us several boxes of minerals, rocks and fossils he had acquired in his lifelong passion for geology. (George was a geology major at Wooster in the class just after mine.) Among the many world-class specimens he gave us are two fossil ophiuroids (brittle stars). They are Ophiopetra lithographica Enay and Hess, 1962, from the Lower Hienheim Beds (Lower Tithonian, Upper Jurassic) near Regensburg, Germany. They are part of the “Fossillagerstätte Hienheim“, a preserved brittle star ecosystem in a lagoon at the edge of a Late Jurassic sea. This is the same set of lithographic limestones in which the famous bird fossil Archaeopteryx was found.
In both these images you see the spiny arms of the brittle stars twisted about. It is their flexibility and snake-like movements in life that provoked the scientific name ophiuroids (serpent-forms) for the brittle stars. The “brittle” term comes from their ability to autotomize (spontaneously detach) their arms when threatened, leaving a squirming distraction for a predator as they escape.
Ophiopetra lithographica is probably the most common fossil brittle star known. It was preserved by the countless millions in these Jurassic lagoons in Germany. Most geologists believe they were buried by fine-grained carbonate sediment suspended by sudden storms. As you can see in the above close-up, the preservation of the plates and spines is remarkable.

Most brittle stars are suspension feeders (sorting out food particles from the water), deposit feeders (eating organic material in the sediment) or scavengers. Ophiopetra lithographica may have been a carnivore with its heavily-spined arms and strong jaws. It likely ate small arthropods on the seafloor.

The evolution of brittle stars is interesting and controversial. They were relatively common in the Paleozoic and then just barely survived the Permian extinctions. Their rapid evolution into a variety of taxa in the Mesozoic and Cenozoic has led to many debates about their phylogeny. Even the placement of Ophiopetra into a family is a problem. Does it belong to the Family Aplocomidae where it was originally placed or to the older Family Ophiolepididae as has been recently suggested?

Our students will enjoy these fine fossils in the invertebrate paleontology course. They have doubled our collection of brittle stars! Thank you again to George Chambers for his thoughtfulness and generosity.

References:

Enay, R. and Hess, H. 1962. Sur la découvertes d’Ophiures (Ophiopetra lithographica n.g. n.sp.) dans le Jurassique supérieur du Haut-Valromey (Jura méridional). Eclogae geologicae Helvetiae 55: 657-678.

Hess, H. and Meyer, C.A. 2008. A new ophiuroid (Geocoma schoentalensis sp. nov.) from the Middle Jurassic of northeastern Switzerland and remarks on the Family Aplocomidae Hess 1965. Swiss Journal of Geosciences 101: 29-40.

Röper, M. and Rothgänger, M. 1998. Die Plattenkalke von Hienheim (Landkreis Kelheim) – Echinodermen-Biotope im Südfränkischen Jura. Eichendorf (Eichendorf Verlag), 110 S.

Stöhr, S. 2012. Ophiuroid (Echinodermata) systematics—where do we come from, where do we stand and where should we go? In: Kroh, A. and Reich, M. (Eds.) Echinoderm Research 2010: Proceedings of the Seventh European Conference on Echinoderms, Göttingen, Germany, 2–9 October 2010. Zoosymposia, 7: 147-161.

Thuy, B., Klompmaker, A.A. and Jagt, J.W.M. 2012. Late Triassic (Rhaetian) ophiuroids from Winterswijk, the Netherlands; with comments on the systematic position of Aplocoma (Echinodermata, Ophiolepididae). In: Kroh, A. and Reich, M. (Eds.) Echinoderm Research 2010: Proceedings of the Seventh European Conference on Echinoderms, Göttingen, Germany, 2–9 October 2010. Zoosymposia, 7: 163-172.

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Mark Wilson March 3rd, 2013

This is the inside of a modern cockle shell (Dinocardium vanhyningi) found on a beach in Wilmington, North Carolina. Across the surface is a radiating series of pits, each of which was formed under a zooid of an encrusting cheilostome bryozoan colony, much like Ropalonaria described last week. This etched shell gives me an opportunity to tell a cautionary tale of trace fossils, slugs and taxonomy.
This scanning electron microscope image was taken by my friend and colleague Paul Taylor at The Natural History Museum in London. It shows a cheilostome bryozoan etching (the elongated pits) across a shell surface very much like the modern shell at the top of the page. In the lower right is a bit of the cheilostome bryozoan Amphiblestrum. This particular bryozoan did not make the pits themselves (it is oriented in a different direction), but another colony of the same species likely did. This assemblage comes from the Coralline Crag Formation (Pliocene) exposed in Broom Pit, Suffolk, England.

In 1999, Paul Taylor, Richard Bromley and I published a paper in the journal Palaeontology describing these bryozoan etching pits as a new ichnogenus (a category of trace fossil) with a Late Cretaceous to Holocene range. We invented (or so we thought) the name Leptichnus using the Greek roots leptos (‘flimsy, delicate, subtle’) and ichnos (‘track, footprint’). It was a fun little project, and we provided a useful name to embed this fossil in the literature.

This past fall, thirteen years after publication, I decided to write a Fossil of the Week entry on Leptichnus. In my innocence I searched Google for “Leptichnus” and was very surprised to find it has a Wikipedia page — and it was an East African slug! Yes, the beautiful name Leptichnus was preoccupied by a urocyclid terrestrial gastropod, Leptichnus Simroth, 1896, found in Kenya and Tanzania. 1896 is a long time before 1999, so Simroth’s name has priority over ours. The ichnogenus Leptichnus Taylor, Wilson and Bromley, 1999, thus became a junior homonym of the gastropod genus Leptichnus Simroth, 1896. We had to come up with a new name for it.
Above is the original 1896 description of Leptichnus The Slug by Heinrich Rudolf Simroth (1851-1917). He apparently came up with the name because this shell-less snail left a subtle trail behind it when it slithered. It is the first time I’ve seen the -ichnus suffix used for anything but a trace fossil.
Herr Doktor Professor Simroth was a German zoologist and malacologist educated at the University of Leipzig. He was a schoolteacher for his whole career, doing prodigious research in his spare time. His speciality was, unsurprisingly, terrestrial slugs. He worked on specimens brought back by scientific expeditions, including one in the short-lived colony of German East Africa. It is from this collected material he described Leptichnus. Simroth’s type collection was long considered lost, but many specimens were recently rediscovered in Berlin (Glaubrecht, 2010). These do not, alas, include any representatives of Leptichnus. The image above is of Simroth in 1902.

Taylor, Wilson and Bromley (2013) proposed the new name Finichnus to replace Leptichnus Taylor, Wilson and Bromley, 1999. To preserve the meaning of the original name, we substituted the Greek finos (‘fine, delicate’) for leptos.

The lesson of this story? Search, search, search for homonyms of new taxonomic names. In our defense, searching wasn’t as easy back in the 90s (Google’s search engine came online in 2000, for example, and Wikipedia began in 2001). At least the adventure introduced us to Heinrich Rudolf Simroth and his slugs!

References:

Glaubrecht, M. 2010. Slug(-gish) science, or an annotated catalogue of the types of tropical vaginulid and agriolimacid pulmonates (Mollusca, Gastropoda), described by Heinrich Simroth (1851–1917), in the Natural History Museum Berlin. Zoosystematics and Evolution 86: 15–335.

Rosso, A. 2008. Leptichnus tortus isp. nov., a new cheilostome etching and comments on other bryozoan-produced trace fossils. Studi Trentini – Acta Geologica 83: 75–85.

Simroth, H. 1896. Über bekannte und neue Urocycliden. Abhandlungen der Senckenbergischen Naturforschenden Gesellschaft 19: 281–312.

Taylor, P.D., Wilson, M.A. and Bromley, R.G. 1999. Leptichnus, a new ichnogenus for etchings made by cheilostome bryozoans into calcareous substrates. Palaeontology 42: 595–604.

Taylor, P.D., Wilson, M.A. and Bromley, R.G. 2013. Finichnus, a new name for the ichnogenus Leptichnus Taylor, Wilson and Bromley, 1999, preoccupied by Leptichnus Simroth, 1896 (Mollusca, Gastropoda). Palaeontology (in press).

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Mark Wilson February 24th, 2013

Another trace fossil of a sort this week. Above you see the dorsal valve exterior of a strophomenid brachiopod from the Upper Ordovician of southeastern Indiana. Across the surface is a network of grooves looking a bit like a spider web. This is a feature formed when a soft-bodied ctenostome bryozoan colony etched its way down into the shell it was encrusting. Ropalonaria venosa Ulrich, 1879 is the official name of this fossil.
Above is a closer view of the same Ropalonaria venosa. Tiny crystals of yellow dolomite fill the excavations. The ctenostome bryozoan that made it had no skeleton and used some sort of chemical to dissolve the shell beneath it. The fidelity of this etching is good enough to identify various details of the colony structure and zooecial form. This is where our fossil classification system goes a bit awry: Is Ropalonaria a trace fossil (evidence of animal activity) or a kind of external mold of the original organism? Arguments have been made for each category, and the name Ropalonaria shows up on lists of both trace fossils and body fossils.
Ropalonaria venosa is the type species of the genus Ropalonaria erected by Edward Oscar Ulrich in 1879 (above in 1927). E.O. Ulrich, as he is better known, was one of the most colorful and controversial geologists of the late 19th and early 20th century. He was born in Covington, Kentucky, in 1857. Covington is across the Ohio River from Cincinnati, Ohio, and is undergirded by the famous fossiliferous limestones and shales of the Cincinnatian Group (Upper Ordovician). Ulrich started as a child collecting fossils in the region. He was an early member of the Cincinnati Society of Natural History, often bringing fossils to meetings for identifications. (There he met another young man very interested in fossils: the future paleontologist Charles Schuchert. Schuchert was the advisor of my advisor’s advisor, so he’s in my “academic genealogy”.)

Ulrich took courses at German Wallace College (today’s Baldwin Wallace University in Berea, Ohio) and the Ohio Medical College. He had an eclectic youth exploring all sorts of topics, from opera to spiritualism, but always kept geology and fossils close to his heart. He had an adventurous stint as a superintendent in a Colorado silver mine. Returning back east, Ulrich became an enormously productive geologist with the geological surveys of Illinois, Minnesota, and Ohio. He was President of the Paleontological Society in 1915. In 1931 he received the Mary Clark Thompson Medal from the National Academy of Sciences, and the next year the Geological Society of America awarded him the prestigious Penrose Medal. He died in 1944 in Washington, D.C.

E.O. Ulrich is still a polarizing figure in American geology. He is famous for resisting the modern concept of facies in sedimentary geology, preferring a concept now known as “layer cake stratigraphy“. (In his defense, the rocks in the Cincinnati area really do fit much of his model; his error was extending it much too far.) Ulrich also has a reputation as a bit of a “splitter” in paleontology. (Someone who makes more species than necessary by “splitting” groups into smaller subgroups.)

Despite what we think of E.O. Ulrich today, his paleontological contributions have mostly held up, including the description of the intriguing fossil Ropalonaria.

References:

Bassler, R.S. 1944. Memorial to Edward Oscar Ulrich. Proceedings of the Geological Society of America for 1944: 331–351.

Pohowsky, R.A. 1978. The boring ctenostomate Bryozoa: taxonomy and paleobiology based on cavities in calcareous substrata. Bulletins of American Paleontology 73(301): 192 p.

Ruedemann, R. 1946. Biographical memoir of Edward Oscar Ulrich, 1857-1944. National Academy of Sciences of the United States of America. Biographical Memoirs, Volume XXIV, 7th Memoir, 24 pp.

Ulrich, E.O. 1879. Descriptions of new genera and species of fossils from the Lower Silurian about Cincinnati: Journal of the Cincinnati Society of Natural History 2: 8-30.

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Mark Wilson February 17th, 2013

The scanning electron microscope (SEM) image above shows the tubes of the encrusting group known as hederelloids. They are among my favorite fossils. I was reminded of them recently while reading this advertisement for a novel in which, to my great surprise, hederelloids are a primary part of the plot! A mysterious black “fouling” destroys shipping. Scientists discover that it is made by a group long thought to be extinct — the hederelloids! There is even a page talking about the “science” behind the story. (Although I would think if they were serious they would spell “bryozoan” correctly.)
The hederelloids are a group of colonial encrusting organisms found from the Silurian through the Permian, with possible members in the Ordovician and the Triassic (Taylor and Wilson, 2008). They were entirely marine and were most common by far on Devonian brachiopods and corals. They are “runner-like” encrusters, meaning they grew sequentially across the substrate budding out new members of the colony. Their zooids (the skeletons that contained the individuals) are usually curved and made of microprismatic calcite secreted from the inside only. (This latter feature meant they could repair damage such as boreholes with patches from the inside; see Wilson and Taylor, 2006). The specimen above is a Devonian spiriferid brachiopod from northwestern Ohio with a hederelloid colony encrusting the dorsal valve.
Hederelloids were very diverse in their time. The SEM image above (courtesy of Paul Taylor at the Natural History Museum, London) shows at least two types of hederelloid on a rugose coral from the Devonian of New York. The large tube at the bottom has several lateral buds. At the very top of the view you can see a much smaller hederelloid growing in the opposite direction.
The earliest workers on hederelloids thought that they were cyclostome bryozoans of some type (see Bassler, 1939). They look superficially like the common genera Corynotrypa, Cuffeyella and Stomatopora. Hederelloids, though, are significantly larger on the whole, they do not bud in the same pattern as bryozoans, and they do not have lamellar walls. Their shell microstructure and budding patterns suggests instead that they may be related to the phoronids, making them a kind of lophophorate (lophophore-bearing organism; the lophophore is a tentacular feeding device). They could probably, like bryozoans, retract the lophophore into their tubes when necessary. The above photograph shows the underside of a hederelloid colony from the Devonian of Iowa. Note the distinctive budding pattern. The scattered spirals are microconchids.

This is a nice collection of hederelloids from the Devonian of New York. Notice the diversity of sizes, shapes and budding patterns. How can you not be fascinated by such enigmatic little creatures?

References:

Bassler, R.S. 1939. The Hederelloidea. A suborder of Paleozoic cyclostomatous Bryozoa. Proceedings of the United States National Museum 87: 25-91.

Taylor, P.D. and Wilson, M.A. 2008. Morphology and affinities of hederelloid “bryozoans”, p. 301-309.  In: Hageman, S.J., Key, M.M., Jr., and Winston, J.E. (eds.), Bryozoan Studies 2007: Proceedings of the 14th International Bryozoology Conference, Boone, North Carolina, July 1-8, 2007.  Virginia Museum of Natural History Special Publication 15.

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

Wilson, M.A. and Taylor, P.D. 2006. Predatory drillholes and partial mortality in Devonian colonial metazoans. Geology 34:565-568.

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Mark Wilson February 10th, 2013

What you see above is a bit of oyster shell with some curious small gouges in it. The oyster is Ilymatogyra (Afrogyra) africana (Lamarck, 1801) from the En Yorqe’am Formation (Cenomanian) exposed in Hamakhtesh Hagadol, southern Israel. The deep scratches are the trace fossil Gnathichnus pentax Bromley, 1975. As you can just make out in the lower center of the image, the grooves are overlapping series of five-pointed stars. That’s what makes this trace so cool — the stars were made by the unique feeding apparatus of a regular echinoid (sea urchin).
This is the business end of the modern sea urchin Strongylocentrotus purpuratus (a preserved specimen in Wooster’s collection). You see here in the center the peristome, which is a circle of plates surrounding the mouth, with the sharp five-sided teeth protruding from the echinoid’s Aristotle’s Lantern. These animals slowly graze across hard substrates, using their teeth to scrape the surfaces for algae, fungi and adherent organisms like diatoms. The biting actions of the Aristotle’s Lantern produce the star-shaped incisions we know as the trace fossil Gnathichnus pentax.

I briefly sampled and studied an exposure of the fossiliferous En Yorqe’am Formation in 2003 during my first visit to Israel. The oyster shells in this unit provide one of the few examples of hard substrate communities in the tropics of the Late Cretaceous. The encrusters include ostreid and spondylid bivalves, the cyclostome bryozoan Stomatopora, and the agglutinating foraminiferan Acruliammina. Borings include those of barnacles (Rogerella elliptica) and sponges (Entobia aff. E. megastoma). There is also a sea urchin present (Heterodiadema lybicum) that was almost certainly the maker of the Gnathichnus pentax traces.

References:

Bromley, R.G. 1975. Comparative analysis of fossil and recent echinoid bioerosion. Palaeontology 18: 725-739.

Wilson, M.A. 2003. Paleoecology of a tropical Late Cretaceous (Cenomanian) skeletozoan community in the Negev Desert of southern Israel. Geological Society of America Abstracts with Programs 35(6): 420.

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Mark Wilson February 3rd, 2013

What we have above is a heliolitid coral known as Protaraea richmondensis Foerste, 1909. It has completely encrusted a gastropod shell with its thin corallum. Stephanie Jarvis, a Wooster student at the time and now a graduate student at Southern Illinois University, found this specimen during her paleontology class field trip to the Whitewater Formation exposed near Richmond, Indiana.

Protaraea is a confusing taxon to my Invertebrate Paleontology students. It is a very common encruster in their Ordovician field collections, being found on hard substrates as varied as rugose corals and orthid brachiopods. It is so thin, though, that it is hard to believe it was a colonial coral. Plus it has tiny septa (vertical partitions) in its corallites (the holes that held the polyps), very unlike most corals of the heliolitid variety. This is a group the students have to identify by matching pictures and taking our word for it.

We can’t identify the gastropod underneath. Note that it has a sinus evident in the last whorl (an open slot parallel to the coiling). The coral grew right up to the edge of this sinus, preserving it and its extension through the shell.

References:

Alexander, R.R. and Scharpf, C.D. 1990. Epizoans on Late Ordovician brachiopods from southeastern Indiana. Historical Biology 4: 179-202.

Foerste, A.F. 1909. Preliminary notes on Cincinnatian fossils. Denison University, Scientific Laboratories, Bulletin 14: 208-231.

Mõtus, M.-A. and Zaika, Y. 2012. The oldest heliolitids from the early Katian of the East Baltic region. GFF 134: 225-234.

Ospanova, N.K. 2010. Remarks on the classification system of the Heliolitida. Palaeoworld 19: 268–277.

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Mark Wilson January 27th, 2013

My Invertebrate Paleontology students know this as Specimen #8 in the trace fossil exercises section: “the big swirly thing”. It is a representative of the ichnogenus Zoophycos Massalongo, 1855. This trace is well known to paleontologists and sedimentologists alike — it is found throughout the rock record from the Lower Cambrian to modern marine deposits. It has a variable form but is generally a set of closely-overlapping burrow systems that produce a horizontal to oblique set of spiraling lobes. It was produced by some worm-shaped organism plunging into the sediments in a repetitive way, gradually making larger and larger downward-directed swirls.

Zoophycos is a useful indicator of ancient depositional conditions. It give its name, in fact, to an ichnofacies — a set of fossils and sediments characterize of a particular environment. In the Paleozoic it is found in shallow water and slope environments; from the Mesozoic on it is known almost entirely from deep-sea sediments. Our specimen is from the Borden Formation and was found amidst turbidite deposits, so it is probably from an ancient slope system.

There has been much debate about the behavior and objectives of the organisms who made Zoophycos. The traditional view is that it was formed by an animal mining the sediment for food particles, a life mode called deposit-feeding. Some workers, though, have suggested it could have been a food cache, a sewage system, and even an agricultural garden of sorts to raise fungi for food. I think in the end the simplest explanatory model is deposit-feeding, although with such a long time range, a variety of behaviors likely produced this trace.

Zoophycos was named in 1855 by the Italian paleobotanist Abramo Bartolommeo Massalongo (1824-1860). Massalongo was a member of the faculty of medicine at the University of Padua, chairing their botany department. (Medicine had broad scope in those days!) Why was he studying this trace fossil? Like most of the early scientists who noticed trace fossils, he thought it was some kind of fossil plant.
Zoophycos villae (Massalongo, 1855, plate 2)

References:

Bromley, R.G. 1991. Zoophycos: strip mine, refuse dump, cache or sewage farm? Lethaia 24: 460-462.

Ekdale, A.A. and Lewis, D.W. 1991. The New Zealand Zoophycos revisited: morphology, ethology and paleoecology. Ichnos 1: 183-194.

Löwemark, L. 2011. Ethological analysis of the trace fossil Zoophycos: Hints from the Arctic Ocean. Lethaia 45: 290–298.

Massalongo, A. 1855. Zoophycos, novum genus Plantarum fossilum, Typis Antonellianis, Veronae, p. 45-52.

Olivero, D. 2003. Early Jurassic to Late Cretaceous evolution of Zoophycos in the French Subalpine Basin (southeastern France). Palaeogeography, Palaeoclimatology, Palaeoecology 192: 59-78.

Osgood, R.G. and Szmuc, E.J. 1972. The trace fossil Zoophycos as an indicator of water depth. Bulletin of American Paleontology 62 (271): 5-22.

Sappenfield, A., Droser, M., Kennedy, M. and Mckenzie, R. 2012. The oldest Zoophycos and implications for Early Cambrian deposit feeding. Geological Magazine 149: 1118-1123.

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Mark Wilson January 20th, 2013

We haven’t had a pseudofossil in this space for awhile. A pseudofossil is an object that is often mistaken for a fossil but is actually inorganic. The above may look like  fossil fern, but it is instead a set of beautiful manganese dendrites in the Solnhofen Limestone (Jurassic) of Germany (scale in millimeters). I put this photo on Wikipedia a long time ago as manganese dendrites. That didn’t stop one website from still using it as an example of a fossil.

Manganese dendrites are thin, branching crystals that grew over a surface in a rock or mineral. Often they are found in cracks or along bedding planes (as in the above example). These dendrites are usually some variety of manganese oxide. The minerals represented can include hollandite, coronadite, and cryptomelane. Apparently they are never pyrolusite, despite what you may see in textbooks. It is also impossible to tell the mineralogy from the shape of the dendrites alone.

How can you tell this is not a fossil plant? For one, the branches are too perfect: none overlap or are folded over or broken as you would expect in a buried three-dimensional plant. Next you’ll notice that all the branches extend from a line at the bottom of the image rather than from a single branching point. Finally, there is no distinction between branch, stem or leaf; instead it is a fractal-like distribution of tiny sharp-edged crystals.

As a bonus, check out this benefit you get from having manganese dendrites:

“Metaphysically, stones with dendrites resonate with blood vessels and nerves. They help heal the nervous system and conditions such as neuralgia. Dendrites can help with skeletal disorders, reverse capillary degeneration and stimulate the circulatory system. It is the stone of plenitude; it also helps create a peaceful environment and encourage the enjoyment of each moment. Dendrites deepen your connection to the earth and can bring stability in times of strife or confusion.”

The Stone of Plenitude! (I hope you do see my sarcasm here …)

This post, by the way, marks the completion of the second year of Wooster’s Fossils of the Week. So far we’ve had 104 posts. Check out our very first edition about a sweet auloporid coral!

References:

Potter, R.M. and Rossman, G.R. 1979. The mineralogy of manganese dendrites and coatings. American Mineralogist 64: 1219-1226.

Post, J.E. and McKeown, D.A. 2001. Characterization of manganese oxide mineralogy in rock varnish and dendrites using X-ray absorption spectroscopy. American Mineralogist 86: 701-713.

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Mark Wilson January 13th, 2013

Like all those who teach, I learn plenty from my students, sometimes with a simple question. Richa Ekka (’13) asked me last semester during a paleontology lab if the above specimen was really a trace fossil as I had labeled it. I collected this curious fossil many years ago and had assumed then and ever since that it was an odd burrow system preserved on the base of a bed of limestone. That I had no idea what kind of trace fossil it was didn’t seem to bother me. When Richa questioned the specimen, I picked it up and looked closely and saw that, indeed, it had a reticulate structure (shown below) that demonstrated it was certainly no fossil burrow. Richa was right.
I began to search the paleontological literature for Ordovician sponges and quickly found the genus Pattersonia Miller, 1889, in the Family Pattersoniidae Miller, 1889, of the Class Hexactinellida (below). The lobes on this specimen match those of our fossil very closely, as does the more detailed reticulate structure.
Pattersonia aurita (Beecher), Brannon, A.M. Peter farm, northern Fayette  County, Kentucky (from McFarlan, 1931).

After reviewing more articles, it is clear that the Wooster sponge is Pattersonia ulrichi Rauff, 1894. It has doubled our collection of Ordovician sponges. Thanks, Richa!

References:

Finks, R.M. 1967. S.A. Miller’s Paleozoic sponge families of 1889. Journal of Paleontology 41: 803-807.

McFarlan, A.C. 1931. The Ordovician fauna of Kentucky, p. 49-165, in: Jillson, W.R., ed., Paleontology of Kentucky, Kentucky Geological Survey, Frankfort, Kentucky.

Rauff, H. 1894. Palaeospongiologie. E. Schweizer-bartśche Verlagsbuchhandlung (E. Koch.).

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Mark Wilson January 6th, 2013

This week’s fossil is not technically impressive: it is a rather modestly preserved conulariid from the Waynesville Formation of southern Indiana (location C/W-111). It is notable because it is one of the very few conulariids I’ve found in the Ordovician, and it gives me a chance to write about a fascinating talk three of my friends presented last month at the annual meeting of the Palaeontological Association in Dublin.

The above image is a side view of the specimen. Its identity as a conulariid is indicated by the four flat sides with gently curved ridges and the distinctive grooved corner between the two visible sides. With only this part of the conulariid visible, we can at least tentatively identify the specimen as Conularia formosa Miller & Dyer, 1878. Conulariids are most likely the polyp stages of scyphozoans (typical “jellyfish”).
Here is a closer view of one of the sides. You can just make out a midline running parallel to the axis of the fossil slightly offsetting the ridges.
This is a broken cross-section through the conulariid showing the four corners and sides. Note that the fossil is symmetrical, give or take a little squishing during preservation. (The test was made of a flexible periderm, not a hard shell.)

This brings us to the presentation last month at the Palaeontological Association meeting titled: “Asymmetry in conulariid cnidarians and some other invertebrates”. It was given by Consuelo Sendino from the Natural History Museum in London, with co-authors Paul Taylor (also NHM London) and Kamil Zágoršek (Národní muzeum, Prague). The specimens below are part of a set of conulariids they studied from the Upper Ordovician (Sandbian) of the Czech Republic.
This is Metaconularia anomala (Barrande, 1867). Note that it has a very different symmetry from the typical conulariid: it is four-sided at the base and three-sided at the top. Only a minority of specimens show this asymmetry, but why any do is a mystery.
Here are several more Metaconularia anomala specimens with various states of symmetry. All are internal molds.
This is a summary of the symmetries present in these Ordovician conulariids. For such a simple morphology, these are surprisingly complex states. There is a pattern to this diversity: these conulariids show a kind of sinistral coiling — a directional asymmetry.

There are many questions that arise from such asymmetrical fossils. Why was the original symmetry “broken” in these individuals? Did asymmetry have adaptive value? (These aberrant individuals apparently survived to a normal size, at least.) Is this asymmetry genetically controlled or produced by the environment in some way? If there is a genetic component, has it ever had evolutionary value?

I now notice fossils that are outside normal symmetry ranges (like this Devonian brachiopod) and wonder how common and important the phenomenon is. Another paleontological wonder and mystery!

References:

Miller, S.A. and Dyer, C.B. 1878. Contributions to Palaeontology (No. 1). Journal of the Cincinnati Society of Natural History 1, no. l, p. 24-39.

Sendino, C., Zágoršek, K. and Taylor, P.D. 2012. Asymmetry in an Ordovician conulariid cnidarian. Lethaia 45: 423-431.

Van Iten, H. 1991. Evolutionary affinities of conulariids, p. 145-155; in Simonetta, A.M. and Conway Morris, S. (eds.). The Early Evolution of Metazoa and the Significance of Problematic Taxa. Cambridge University Press, Cambridge.

Van Iten, H. 1992. Morphology and phylogenetic significance of the corners and midlines of the conulariid test. Palaeontology 35: 335-358.

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