A paleontology field trip into the Upper Ordovician of Ohio

September 8th, 2013

DSC_2515The 2013 Invertebrate Paleontology class at Wooster had its first field trip today. The weather was absolutely perfect, and the usual boatload of fossils was collected. We traveled this year to Caesar Creek State Park and worked in the emergency spillway created and maintained by the US Army Corps of Engineers for the Caesar Creek Lake dam. Exposed here are the Arnheim, Waynesville, Liberty and Whitewater Formations of the Richmondian Stage in the Cincinnatian Series of the Ordovician System. These units are enormously rich with fossils, especially brachiopods, bryozoans, trilobites, clams, snails, nautiloids, corals and crinoids. There is no better place to get students started on paleontological fieldwork, and to follow up with lab preparation, identification and interpretation throughout the semester.

Spillway090813The Caesar Creek Lake emergency spillway is at N 39.480069°, W 84.056832° along Clarksville Road just south of the dam. The authorities keep it clear of vegetation, and so it is an extensive exposure of bare rock and sediment. The sharp southern boundary is the rock wall shown in the top image (with the intrepid Willy Nelson and Zach Downes). Students quickly fanned out along the entire exposure, so I never did get an image of the whole class of 22 students in one place.

DSC_2505This is the bedding plane of a slab of micritic limestone with numerous worm burrows. Trace fossils are very abundant here. These units, in fact, have some of the first trace fossils to be specifically described in North America.

DSC_2506On some limestone slabs are internal and external molds of straight orthocerid nautiloids. They are often paired like this, with both facing in the same direction. This is an effect of seafloor currents that oriented the shells. The current here was flowing from the left to the right.

DSC_2508Many of the limestones are extremely rich in shelly fossils. Here you can see several types of brachiopods, an isotelid trilobite genal spine, and some molluscan internal molds.

DSC_2511I always check in here with my favorite borings: Petroxestes pera. These are bivalve incisions on a cemented seafloor (a carbonate hardground). This is the type area for this ichnogenus and ichnospecies.

DSC_2512Two of our sophomore paleo students, Michael Williams and Adam Silverstein, are here happily filling their sample bags with fossils. I wanted to get a photo of them in the field because they had such a geologically adventurous summer in both cool and wet Iceland and hot, dry Utah. Not many sophomores have these opportunities!

DSC_2520Here is another pair of nautiloids, this time showing the characteristic internal mold features of curved septal walls. Again they are nestled together and oriented because of seafloor currents.

For the rest of the semester the paleo students will be studying the fossils they collected today, each eventually constructing a paleoecological interpretation based on their identifications and growing knowledge of marine invertebrate life habits and history. Now we’re really doing paleontology!

Wooster’s Fossil of the Week: An asaphid trilobite from the Middle Ordovician of the Leningrad Region, Russia

May 5th, 2013

Asaphus lepidurus Nieszkowski, 1859aThis weathered trilobite is nothing like the gorgeous specimens of this genus you can buy at various rock shops around the world and on the web, but it has sentimental value to me. I collected it on an epic field trip in Russia in 2009. We hacked our way through the woods to an exposure of the Frizy Limestone (Volkhov Regional Stage, Darriwilian Stage, Middle Ordovician) where the local people had a side industry of quarrying out these trilobites for international trade. This specimen was the best I found, and it was probably abandoned by other collectors as too damaged. Still, it makes a nice reminder of my Russian experience and I keep it on a cabinet in my office. (By the way, I did not make a Cold War mistake in referring to the “Leningrad Region“. This oblast retains the old name of the city now known as St. Petersburg. Apparently the residents voted to keep it that way after the Soviet Union collapsed.)
Asaphus lepidurus Nieszkowski, 1859bThis is the asaphid trilobite Asaphus lepidurus Nieszkowski, 1859. This group is known for having fantastic eyes, some on long stalks and others with calcareous “eyeshades” above them. This species has more conventional eyes, but they’re still cool.
Asaphus lepidurus Nieszkowski, 1859cA. lepidurus studies us with a cold, dead eye. From this perspective the facial suture is visible as the curved, raised line running from the near eye to the periphery of the cephalon (head). This is a line of weakness the trilobite used to split its exoskeleton for molting (ecdysis). These sutures often have diagnostic value for distinguishing trilobites, especially at the species level.

A. lepidurus was first described and named by Jan Nieszkowski (1833-1866), a Polish paleontologist (and naturalist and medical doctor). He was born in Lublin, Poland, son of an army captain. He studied at the University of Dorpat (now the University of Tartu in Estonia) and soon became an avid and productive paleontologist. He then participated in the January Uprising of Poles against the occupying Russians in 1863. He was captured and exiled to the Russian city of Orenburg, where he died at a young age of typhus.

This little trilobite brings back memories of my Russian adventure, and it is also a reminder that science is never done in a political vacuum. Here’s to the Polish patriot and scientist Dr. Jan Nieszkowski.

References:

Dronov, A., Tolmacheva, T., Raevskaya, E., and Nestell, M. 2005. Cambrian and Ordovician of St. Petersburg region. 6th Baltic Stratigraphical Conference, IGCP 503 Meeting; St. Petersburg, Russia: St. Petersburg State University.

Ivantsov, A.Y. 2003. Ordovician trilobites of the Subfamily Asaphinae of the Ladoga Glint. Paleontological Journal 37, supplement 3: S229-S337.

Nieszkowski, J. 1859. Zusätze zur Monographie der Trilobiten der Ostseeprovinzen, nebst der Beschreibung einiger neuen obersilurischen Crustaceen. Archiv für die Naturkunde Liv-, Ehst-, und Kurland, Serie 1: 345-384.

Wooster’s Fossil of the Week: Tubular drillholes (Upper Ordovician of the Cincinnati Region)

April 28th, 2013

Trypanites_hardground_585_010213

This is one of the simplest fossils ever: a cylindrical hole drilled into a hard substrate like a skeleton or rock. The above image is of a hardground (cemented carbonate seafloor) from the Upper Ordovician of northern Kentucky with these borings cut perpendicularly to the bedding and descending downwards. Each boring is filled with light-colored dolomite crystals. This boring type is given the trace fossil name Trypanites weisi Magdefrau 1932.
Trypanites_Bryozoan_010213_585Trypanites, shown above cutting into a trepostome bryozoan from the Upper Ordovician of southeastern Indiana, is a very long-ranging trace fossil. It first appears in the Lower Cambrian and it is still formed today — a range of 540 million years (James et al., 1977; Taylor and Wilson, 2003). It was (and is) made by a variety of worm-like organisms, almost always in carbonate substrates. Today the most common producers of Trypanites are some polychaete and sipunculid worms. Trypanites was the most common boring until the Jurassic, when it was overtaken in abundance by bivalve and sponge borings. Trypanites was the primary boring in the Ordovician Bioerosion Revolution (Wilson and Palmer, 2006).
Trypanites_Horizontal_585Trypanites is defined as a cylindrical, unbranched boring in a hard substrate (such as a rock or shell) with a length up to 50 times its width (Bromley, 1972). The typical Trypanites is only a few millimeters long, but some are known to be up to 12 centimeters in length (Cole and Palmer, 1999). The above occurrence of Trypanites is one of my favorites. The organisms bored into a bryozoan colony (the fossil in the upper left and center with tiny holes) and down into a bivalve shell the bryozoan had encrusted. The borer then turned 90° and drilled horizontally through the aragonitic and calcitic layers of the shell. The aragonite dissolved, revealing the half-borings of Trypanites.
LibertyBorings_585In this bedding plane view, Trypanites weisi borings are shown cutting into a hardground from the Liberty Formation (Upper Ordovician) of southeastern Indiana. This is a significant occurrence because the borings are cutting through brachiopod shells cemented into the hardground surface. When the brachiopods are dislodged from the hardground, those with holes in them erroneously appear to have been bored by predators (see Wilson and Palmer, 2001).

The simplest of fossils turns out to have its own levels of complexity!

References:

Bromley, R.G. 1972. On some ichnotaxa in hard substrates, with a redefinition of Trypanites Mägdefrau. Paläontologische Zeitschrift 46: 93–98.

Cole, A.R. and Palmer, T.J. 1999. Middle Jurassic worm borings, and a new giant ichnospecies of Trypanites from the Bajocian/Dinantian unconformity, southern England. Proceedings of the Geologists’ Association 110 (3): 203–209.

James, N.P., Kobluk, D.R. and Pemberton, S.G. 1977. The oldest macroborers: Lower Cambrian of Labrador. Science 197 (4307): 980–983.

Taylor, P.D. and Wilson. M.A. 2003. Palaeoecology and evolution of marine hard substrate communities. Earth-Science Reviews 62 (1-2): 1–103.

Wilson, M.A. and Palmer, T.J. 2001. Domiciles, not predatory borings: a simpler explanation of the holes in Ordovician shells analyzed by Kaplan and Baumiller, 2000. Palaios 16: 524-525.

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

Wooster’s Fossil of the Week: A bryozoan etching (Upper Ordovician of Indiana)

February 24th, 2013

Ropalonaria_venosa_585_010213Another 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.
Ropalonaria_close_010513Above 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.
Ulrich_EO_1927Ropalonaria 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.

Wooster’s Fossil of the Week: A very thin coral from the Upper Ordovician of Indiana

February 3rd, 2013

Protaraea111712What 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.

Wooster’s Fossil of the Week: A glass sponge from the Upper Ordovician of southern Ohio

January 13th, 2013

Pattersonia ulrichi Rauff, 1894_585Like 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.
Pattersonia ulrichi closerI 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)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.).

Wooster’s Fossil of the Week: A conulariid from the Upper Ordovician of Indiana

January 6th, 2013

Conulariid123012This 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”).
CloseConulariid123012Here 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.
Cross1123012This 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.
1Screen shot 2012-12-19 at 5.36.04 AMThis 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.
2Screen shot 2012-12-19 at 5.36.27 AMHere are several more Metaconularia anomala specimens with various states of symmetry. All are internal molds.
3Screen shot 2012-12-19 at 5.37.02 AMThis 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.

Wooster’s Fossil of the Week: A bivalve boring from the Upper Ordovician of southern Ohio

December 16th, 2012

This week’s fossil is from close to home. In fact, it sit in my office. The above is a trace fossil named Petroxestes pera. It was produced on a carbonate hardground by a mytilacean bivalve known as Modiolopsis (shown below). Apparently the clam rocked back and forth on this substrate to make a small trench to hold it in place for its filter-feeding. This particular specimen of Petroxestes was found in the Liberty Formation (Upper Ordovician) of Caesar Creek State Park in southern Ohio. This is a place many Wooster paleontology students know well from field trips.
The original Petroxestes was at first known only from the Cincinnatian Group, but now it is known from many other places and time intervals, even including the Cretaceous and Miocene. It is a good lesson about trace fossils. They are defined by their morphology, not what organisms made them. It turns out that this slot-shaped trace can be made by other animals besides Modiolopsis, which went extinct in the Permian.

References:

Jagt, J.W.M., Neumann, C. and Donovan, S.K. 2009. Petroxestes altera, a new bioerosional trace fossil from the upper Maastrichtian (Cretaceous) of northeast Belgium. Bulletin de l’Institut royal des Sciences naturelles de Belgique, Sciences de la Terre 79: 137-145.

Pickerill, R.K., Donovan, S.K. and Portell, R.W. 2001. The bioerosional ichnofossil Petroxestes pera Wilson and Palmer from the Middle Miocene of Carriacou, Lesser Antilles. Caribbean Journal of Science 37: 130-131.

Pojeta Jr., J. and Palmer, T.J. 1976. The origin of rock boring in mytilacean pelecypods. Alcheringa 1: 167-179.

Tapanila, L. and Copper, P. 2002. Endolithic trace fossils in Ordovician-Silurian corals and stromatoporoids, Anticosti Island, eastern Canada. Acta Geologica Hispanica 37: 15–20.

Wilson, M.A. and Palmer, T.J. 1988. Nomenclature of a bivalve boring from the Upper Ordovician of the midwestern United States. Journal of Paleontology 62: 306-308.

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

Wooster’s Fossil of the Week: A horn coral from the Upper Ordovician of Indiana

December 9th, 2012

This week’s fossil is a very common one from the Whitewater Formation (Richmondian, Upper Ordovician) exposed near Richmond, Indiana. It was collected, along with hundreds of other specimens, during one of many Invertebrate Paleontology field trips to an outcrop along a highway. The fossil is Grewingkia canadensis (Billings, 1862), a species my students know well because many made acetate peels of cross-sections they cut through it.

Grewingkia canadensis belongs to the Order Rugosa, a group commonly called the “horn corals” because their solitary forms (as above) have a horn-like shape. Children often think they are dinosaur teeth! It is so common in Richmondian rocks that it is sometimes used to indicate current direction. Its robust skeleton provided attachment space to many encrusting organisms, and it often has multiple borings in its thick calcite theca.

We believe that the rugose corals lived much like corals today. They sat partially buried in the sediment with the wide end of the skeleton facing upwards. A polyp sat inside the cup-shaped opening, spreading its tentacles to catch small organisms swimming by.

Grewingkia canadensis has a complicated taxonomic history. It is likely also known as Streptelasma rusticum, Grewingkia rustica, Streptelasma vagans, Streptelasma insolitum, and Streptelasma dispandum. G. canadensis is characterized by cardinal and counter septa (the vertical partitions inside the coral skeleton) that are longer than the other major septa throughout ontogeny (growth).
The handsome man shown above is, of course, a paleontologist. This is Elkanah Billings (1820-1876), Canada’s first government paleontologist and the one who named Grewingkia canadensis. (He originally placed it in the genus Zaphrentis.) Billings was born on a farm near Ottawa. He went to law school and became a lawyer in 1845. But he loved fossils and in 1852 founded a journal called the Canadian Naturalist (and Geologist). In 1856, Billings left the law and joined the Geological Survey of Canada as its first paleontologist. He named over a thousand new species in his career, and is best known for describing the first fossil from the Ediacaran biota — a critical time in life’s early history. The Billings Medal is given annually by the Geological Association of Canada to the most outstanding of its paleontologists.

References:

Billings, E. 1862. New species of fossils from different parts of the Lower, Middle, and Upper Silurian rocks of Canada. Paleozoic Fossils, Volume 1, Canadian Geological Survey, p. 96-168.

Elias, R.J. and Lee, D.J. 1993. Microborings and growth in Late Ordovician halysitids and other corals. Journal of Paleontology 67: 922-934.

Elias, R.J., McAuley, R.J. and Mattison, B.W. 1987. Directional orientations of solitary rugose corals. Canadian Journal of Earth Sciences 24: 806-812.

Wooster’s Fossil of the Week: A gumdrop bryozoan (Middle Ordovician of eastern Iowa)

November 25th, 2012

This simple, rounded fossil with tiny holes on its surface is the trepostome bryozoan Prasopora falesi (James, 1884) from the Middle Ordovician Galena Group of eastern Iowa. It was collected with dozens of others on an Independent Study field trip in 2003 with Aaron House (2004). Aaron was studying the paleoecology of these bryozoans; he was especially interested in borings in these calcitic bryozoans called Trypanites.

Part of Aaron’s project involved cutting through these Prasopora colonies to see the borings on the inside. He made acetate peels of polished slabs of the bryozoans, a technique that produces a detailed acetate replica of internal details.
The image above is of one of those acetate peels. You can see the tubular zooecia that contained the original zooids (or individuals) of the bryozoan colony. (They are a series of ellipses because of the angle of the cut and variations in zooecial growth directions.) The black dots are very curious: they are apparently brown bodies, the fossilized remains of the tiny polypides inside the zooecia. These organic remains were replaced by dark minerals and preserved all these 470 million years since.

References:

Anstey, R.L. and Perry, T.G. 1972. Eden Shale bryozoans: a numerical study (Ordovician, Ohio Valley). Michigan State University Publications of the Museum, Paleontological Series, Vol. 1, 80 p.

James, U.P. 1884. Descriptions of four new species of fossils from the Cincinnati Group. The Journal of the Cincinnati Society of Natural History 7: 137-140.

Morrison, S.J. and Anstey, R.L. 1979. Ultrastructure and composition of brown bodies in some Ordovician trepostome bryozoans. Journal of Paleontology 53: 943-949.

Nicholson, H.A. and Etheridge, R., Jr. 1877. On Prasopora Grayae, a new genus and species of Silurian corals. Annals and Magazine of Natural History 4:388–392.

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