Wooster’s Fossil of the Week: An interlocking rugose and tabulate coral (Devonian of Michigan)

February 23rd, 2014

Hexagonaria percarinata colony viewThis beautifully polished fossil looks like half of an antique bowling ball. Normally I hate polished fossils because the external details have been erased, but in this case the smooth surface reveals details about the organisms and their relationship. We have here a large colonial rugose coral with a smaller tabulate coral embedded within it. The specimen is from the Devonian of Michigan. It may look familiar because it is a large “Petoskey Stone“, the state stone (not fossil!) of Michigan. The large rugose coral is Hexagonaria percarinata (Sloss, 1939).
Hexagonaria percarinata close view 585In this closer view you can see the multiple star-like corallites of this coral. Each corallite held a tentacular feeding polyp in life. The radiating lines are thin vertical sheets of skeleton called septa. The corallites in this type of coral shared common walls and nestled up against each other as close as possible. In the lower center of the image you can see a very small corallite that represents a newly-budded polyp inserting itself as the colony grew. If rugose corals were like modern corals (and they probably were), the polyps were little sessile benthic carnivores catching small passing organisms with a set of tentacles. They may also have had photosymbionts to provide oxygen and carbohydrates through photosynthesis.
Tabulate coral intergrown with HexagonariaIn the midst of the rugose coral is this irregular patch with another type of coral: a tabulate coral distinguished by numerous horizontal partitions in its corallites (and no septa). It was likely a favositid coral, sometimes called a “honeycomb coral”. It was clearly living in the rugosan skeleton and not pushed into it by later burial. Note, though, the ragged boundary between the two corals. The rugose coral has the worst of it with some corallites deeply eroded. What seems to have happened is that the rugose coral had an irregular opening in its corallum (colonial skeleton) after death and the tabulate grew within the space, eventually filling it. The tabulate likely stuck out far above the rugose perimeter, but the polishing shaved them down to the same level. This is thus not a symbiotic relationship but one that happened after the death of the rugose coral.
Stumm, Erwin C   copyThe rugose coral species, Hexagonaria percarinata, was named in 1939 by Laurence Sloss, a famous sedimentary geologist with an early start in paleontology, but it is best known through the research of Erwin Charles Stumm (1908-1969; pictured above). Stumm was at the end of his life a Professor of Geology and Mineralogy and the Curator of Paleozoic Invertebrates in the Museum of Paleontology at the University of Michigan. Stumm grew up in California and then moved east for his college (George Washington University, ’32) and graduate (PhD from Princeton in 1936) education. He taught geology at Oberlin College up the road for ten years, and then moved to Michigan to start as an Associate Curator and Assistant Professor. I knew his name because in 1967 he was President of the Paleontological Society. He is said to have been a dedicated teacher of undergraduates and effective graduate advisor. It is fitting that his name is connected to such a popular fossil as Hexagonaria percarinata.

References:

Sloss, L. 1939. Devonian rugose corals from the Traverse Beds of Michigan. Journal of Paleontology 13: 52-73.

Stumm, E.C. 1967. Growth stages in the Middle Devonian rugose coral species Hexagonaria anna (Whitfield) from the Traverse Group of Michigan. Contributions from the Museum of Paleontology, The University of Michigan 21(5): 105-108.

Stumm, E.C. 1970. Corals of the Traverse Group of Michigan Part 13, Hexagonaria. Contributions from the Museum of Paleontology, The University of Michigan 23(5): 81-91.

Citizen scientist to the rescue (in more ways than one)

November 9th, 2013

StephLizzie110913NEW LONDON, OHIO–The Wooster paleontologists spent a pleasant afternoon with our favorite amateur fossil collector Brian Bade. Brian has been mentioned in this blog previously for the many important fossils he has found and donated. He is a spectacular citizen scientist with a deep love (some would say obsession) with fossils of all kinds. He has a tremendous collection of fossils from the region and elsewhere carefully cataloged as to formations and localities. He knows what specimens may have scientific importance, and he has always been most generous with his time and fossils.

Today Steph Bosch (’14), Lizzie Reinthal (’14) and I visited Brian to examine specimens he recently collected from the Waldron Shale (Silurian) exposed in the St. Paul Stone Quarry in St. Paul, Indiana. My colleagues and I need to examine Silurian microconchids from North America and, sure enough, Brian came to the rescue with his collections and eagle eyes. Not only did he have his cleaned and sorted Waldron material laid out for us, he also had segregated specimens that had encrusting microconchids on them. The fossils were fantastic. Check out this webpage to get an idea of the paleontological diversity at this site.

Brian also brought out other trays and boxes of fossils from the Silurian and Early Devonian that had encrusters. Lizzie and Steph proved adept at picking out the tiny microconchids with their bare, young eyes as I struggled with my usual handlens. (This was the typical situation during our fieldwork in Israel this summer as well.) We accumulated several excellent specimens for later study under a Scanning Electron Microscope. Brian once again came through with critical fossils collected with all the right information for scientific analysis.

And the other rescue by Brian? You can see the situation in the image below. After all the driving I did in exotic places this summer, I managed to burrow into deep mud in Brian’s front yard. My little car was completely mired. (Note the smirking students in the background getting ready to tweet photos.) Brian has a tractor, fortunately enough, and a long chain. I left behind two deep trenches in his grass, and a little bit of my pride.
CarStuck110913

Wooster’s Fossils of the Week: Very common orthocerid nautiloids from the Siluro-Devonian of Morocco

November 3rd, 2013

Nautiloids585_092313If you’ve been to a rock shop, or even googled “fossil”, you’ve seen these beautiful and ubiquitous objects. They are polished sections through a nautiloid known as “Orthoceras“. We put quotes around the genus name because with these views it is nearly impossible to identify the actual genus, so “Orthoceras” becomes the go-to term for unknown orthoconic (straight) nautiloids. We also do not know exactly where in Morocco these fossils come from, but chances are they were dug out of the Orthoceras Limestone (Siluro-Devonian) exposed near Erfoud in the Ziz Valley near the edge of the Sahara Desert. They are easily excavated, take a nice polish, and look good from almost any angle of cut. People bring these to me often to ask about their origin, so let’s do a Fossil of the Week about the critters.

These fossil nautiloids consisted in life of a long, straight conical shell with internal chambers pierced by a long tube. The shells were originally made of aragonite, but almost all have been replaced and recrystallized with calcite. A squid-like animal produced the shell. Most of its body was in the large body chamber at the open end of the cone. They were effective nektic (swimming) predators during the Paleozoic Era around the world. In some places (like Morocco) nautiloids were so common that their dead shells carpeted shallow seafloors. Nautilus is a living descendant.
SingleNautiloid092313 annotatedIn this closer cross-sectional view of a Moroccan “Orthoceras“, we can identify the critical parts. A = a chamber (or camera); B = the siphuncle (tube running through the center of the shell); C = a septum that divides one chamber from another; D = an orthochoanitic (straight) septal neck of shell that runs briefly along the siphuncle. The white to gray material is crystalline (“sparry”) calcite that filled the empty shell after death and burial.

By the way, you can buy “Orthoceras healing stones“. A quote from that site: “Fossils are believed to increase life span, reduce toxins, anxiety, stress, balance the emotions, make one more confident. Containing supernatural and physical healing powers. They promote a sense of pride and success in business. Healers use fossils to enhance telepathy and stimulate the mind. Traditionally, fossils have been used to aid in  reducing tiredness, fatigue, digestive disorders, and rheumatism.” No wonder paleontologists are always the very image of health and wealth!
BRUGIEREThe genus Orthoceras was named in 1789 by the French zoologist (and physician) Jean Guillaume Bruguière (1749–1798). The only image I could find of him is the small one above. Bruguière earned a medical degree from the University of Montpellier in 1770, but like many aspiring naturalists, he never practiced. He traveled very widely for an 18th Century scientist, usually to pursue living and fossil mollusks on various expeditions. That he was a Republican in revolutionary France probably saved his head, but he lost his income in the turmoil. Most of his descriptions of fossil taxa appeared in print decades after he died on a voyage back from Persia. Of all his taxonomic contributions, the genus Orthoceras is the most widely known.

References:

Histon, K. 2012. Paleoenvironmental and temporal significance of variably colored Paleozoic orthoconic nautiloid cephalopod accumulations. Palaeogeography, Palaeoclimatology, Palaeoecology 367–368: 193–208.

Kröger B. 2008. Nautiloids before and during the origin of ammonoids in a Siluro-Devonian section in the Tafilalt, Anti-Atlas, Morocco. Special Papers in Palaeontology 79, 110 pp.

Lubeseder, S. 2008. Palaeozoic low-oxygen, high-latitude carbonates: Silurian and Lower Devonian nautiloid and scyphocrinoid limestones of the Anti-Atlas (Morocco). Palaeogeography, Palaeoclimatology, Palaeoecology 264: 195-209.

Wooster’s Fossil of the Week: A strophomenid brachiopod from the Middle Devonian of Michigan

September 1st, 2013

Stropheodonta demissa 585Every year in the first class session of my Invertebrate Paleontology course I give my students each an unknown fossil. It must be something relatively common so that I can give 20 nearly-identical specimens, and it is ideally of a species that can be identified (eventually) using web resources. This year I gave each student the strophomenid brachiopod shown above.

This is Strophodonta demissa (Conrad, 1842) from the Silica Shale Formation (Traverse Group, Givetian, Middle Devonian) exposed in an abandoned quarry near Milan, Washtenaw County, Michigan. These were collected by my friend Brian Bade, an ace amateur paleontologist. In the views above, the shell on the left has the dorsal valve exterior up, and the shell on the right has the ventral valve exterior up. Since the dorsal valve is concave and the ventral valve is convex, this brachiopod shape is called concavo-convex. It also has a long hinge line so we also call it strophic. The fine radiating lines are costae, and so this species is costate. Those characters pretty much define a typical strophomenid brachiopod. (And now all my students understand this, I’m sure.)

Strophodonta is a genus named by the famous American paleontologist James Hall (1811-1898), someone we previously profiled on this blog. The type species of the genus is Strophomena demissa Conrad, 1842, so that name becomes Strophodonta demissa (Conrad, 1842). The author names following taxa are known as the “authority”. They go into brackets for a species that was later placed in another genus. (T.A. Conrad was also mentioned and pictured in a previous entry.)
Screen Shot 2013-08-12 at 3.36.36 PMNow James Hall left us a bit of a puzzle with Strophodonta. In 1852 he published his original description of the genus and called it “Stropheodonta” (see above from the original). Note the addition of the “e”.
Screen Shot 2013-08-12 at 3.33.40 PMHowever, as you see above, in 1858 Hall referred to the same genus and spelled it Strophodonta, without the “e”. This is not only another spelling, it is another pronunciation of the name. He even retroactively refers to his 1852 name as Strophodonta as if he is correcting the spelling. (And indeed, he has “Strophodonta” also in the text of the 1852 monograph, but not in the description.) We’re thus faced with two names for the same genus, which is very naughty in taxonomy for obvious reasons. Today when you search for “Stropheodonta” on Google you get 3850 hits. Searching for “Strophodonta“, though, produces 121,000 hits.

So which spelling is correct? I’ve always used “Stropheodonta“, although now I see that puts me in the minority. A check of the Paleobiology Database shows Stropheodonta and Strophodonta as “alternative spelling” on one page. On another is the unhelpful statement: “It was corrected as Strophodonta by Williams et al. (2000); it was misspelled as Strophodonta by Sepkoski (2002).” (Yes, you have to read it carefully. I cut-and-pasted to make sure I got it as is.)

The Treatise on Invertebrate Paleontology is where we go to resolve problems like this (if an updated version is available). It turns out there that “Stropheodonta” is corrected as Strophodonta. Hall’s retroactive spelling change was accepted and Strophodonta is now the proper spelling and pronunciation. “Stropheodonta” is now a nomen vanum, or “vain name”. This means that it has “unjustified but intentional emendations”.

Ah, the legalese of scientific taxonomy! Obscure but essential for keeping our language relevant and useful.

References:

Conrad, T.A. 1842. Observations on the Silurian and Devonian systems of the United States, with descriptions of new organic remains. Journal of the Academy of Natural Sciences, Philadelphia 8: 228–280.

Hall, J. 1852. Palaeontology of New-York, vol. II. Containing descriptions of the organic remains of the lower middle division of the New-York System (equivalent in parts to the Middle Silurian rocks of Europe). C. Van Benthuysen Printers; Albany, New York, p. 63.

Hall, J. and Whitney, J.D. 1858. Report on the geological survey of the state of Iowa: embracing the results of investigations made during portions of the years 1855, 56 & 57, vol. I, part II: Palaeontology. C. Van Benthuysen Printers; Albany, New York, p. 491.

Williams, A., Brunton, H.C. and Carlson, S.J. 2000. Treatise on Invertebrate Paleontology. Part H, Brachiopoda Revised, Vol. 2: Linguliformea, Craniiformea, and Rhynchonelliformea (part). Treatise on invertebrate paleontology. Geological Society of America, Boulder, Colorado.

Wooster’s Fossil of the Week: Encrusting tubes from the Devonian of Michigan

February 17th, 2013

HederelloidSEM_DevMIThe 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.)
HederellaOH3The 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.
HedsSEMpdtDevNYHederelloids 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.
DevonianIowaHederelloidUSNM78639The 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.

HedCloseUpDevNYThis 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.

Wooster’s Fossil of the Week: A spiriferid brachiopod (Middle Devonian of northwestern Ohio)

October 14th, 2012

I begin my Invertebrate Paleontology course by giving each student a common fossil to identify “by any means necessary”. This year I gave everyone a gray little brachiopod, one of which is shown above. They did pretty well. Kevin Silver (’13) got it down to the genus quickly. Turns out a Google image search on “common fossil” is very effective!

This is Mucrospirifer mucronatus (Conrad, 1841), a beautiful spiriferid brachiopod from the Silica Shale Formation (Middle Devonian) of Paulding County, northwestern Ohio. I collected it and many others at a quarry on a crisp October day with my friend and amateur paleontological colleague Brian Bade.

The image at the head of this page is a view of the dorsal valve exterior of Mucrospirifer mucronatus; the image immediately above is the ventral valve exterior. Spiriferid brachiopods like this are characterized by extended “wings” and a long hingeline. Inside was their defining feature: a spiral brachidium that held a delicate tentacular feeding device known as the lophophore.

This is the anterior of our brachiopod. The fold in the middle helped keep incurrent and excurrent flows separate, enabling more efficient filter-feeding. (By the way, have you noted the quirky asymmetry of this specimen?)

A view of the quarry that yielded our Fossil of the Week. Note the happy amateurs picking through blast piles of the Silica Shale Formation (Middle Devonian).

A pond in the quarry. It has an unexpected beauty, muddy as it is.

Timothy Abbott Conrad (1803-1877) described Mucrospirifer mucronatus in 1841. We met him before when discussing a siliquariid gastropod. He was a paleontologist in New York and New Jersey, and a paleontological consultant to the Smithsonian Institution.

Reference:

Tillman, J.R. 1964. Variation in species of Mucrospirifer from Middle Devonian rocks of Michigan, Ontario, and Ohio. Journal of Paleontology 38: 952-964.

Wooster’s Fossil of the Week: a beautiful phacopid trilobite (Middle Devonian of Ohio, USA)

August 5th, 2012

Trilobites are always favorite fossils, especially big bug-eyed ones like Phacops rana (Green, 1832) shown above. It is, in fact, the state fossil of Pennsylvania after a petition from schoolchildren in 1988. This specimen is from the Middle Devonian of northwestern Ohio. Trilobites were Paleozoic arthropods with a hard dorsal skeleton divided into numerous segments. They look rather cute and brainy because of a swelling between the eyes (the glabella), but that space prosaically contained the stomach. Many trilobites, like this one, could roll up into balls when stressed, much like pill bugs today.

Phacops was studied by paleontologist Niles Eldredge in the early 1970s as the start of what became the theory of punctuated equilibria. The arrangement of lenses in the eyes show rapid changes in short intervals of geological time, which provided evidence for the theory he presented with colleague Stephen Jay Gould.

Phacops rana was named by Jacob Green in 1832. He called it Calymene bufo rana. Hall (1861) renamed it Phacops rana, which was confirmed by Eldedge (1972). Struve (1990) placed it in the new genus Eldredgeops (named after you know who), but I prefer the older name.
Jacob Green (1790-1841) was one of those early 19th Century American polymaths. He was a lawyer, a chemist, a physician, an astronomer, and a paleontologist. He came from a religious family, with both his father and grandfather being theologians. His father, in fact, was at one time president of Princeton University. Jacob graduated from the University of Pennsylvania at the young age of 16, and he published a treatise on electricity when he was 19. He did lawyering for a few years before becoming a professor at (you guessed it) Princeton (and later Jefferson Medical College). He published an amazing array of diverse scientific papers in his career. A trip to England introduced him to trilobites. He then spent a decade putting together a monograph on the trilobites of North America — the first ever.

References:

Eldredge, N. 1972. Systematics and evolution of Phacops rana (Green, 1832) and Phacops iowensis Delo, 1935 (Trilobita) for the Middle Devonian of North America. Bull. Am. Mus. Nat. Hist. 147:45-114.

Eldredge, N. 1973. Systematics of Lower and Lower Middle Devonian species of the trilobite Phacops Emmrich in North America. Bull. Am. Mus. Nat. Hist. 151:285-338.

Green, J. 1832. A Monograph of the Trilobites of North America. Philadelphia.

Hall, J. 1861. Descriptions of new species of fossils from the Upper Helderberg, Hamilton, and Chemung Groups. N.Y. State Cab. Nat. Hist., Ann. Rept. No. 14.

Struve, W. 1990. Paläozoologie III (1986-1990). Courier Forschungsinstitut Senckenberg 127: 251-279.

Wooster’s Fossil of the Week: An asteroid trace fossil from the Devonian of northeastern Ohio

February 12th, 2012

It is pretty obvious what made this excellent trace fossil: an asteroid echinoderm. (The term “asteroid” sounds odd here, but it is the technical term for a typical sea star.) The above is Asteriacites stelliformis Osgood, 1970, from the Chagrin Shale (Upper Devonian) of northeastern Ohio.

We can tell that it was made by a sea star burrowing straight down into the sediment because it has faint chevron-shaped marks in the rays made by tube feet as they moved sediment aside. The mounds of excavated sediment can be seen between the rays at their bases. This tells us that we are not looking at an external mold of a dead sea star, but instead its living activity. This is what a trace fossil is all about.

A living asteroid from the shallow sea off Long Island, The Bahamas. (The hand belongs to my son, Ted Wilson.)

The ichnogenus Asteriacites was named by von Schlotheim in 1820. We profiled him earlier with the genus Cornulites. The author of Asteriacites stelliformis was Richard G. Osgood, Jr., my undergraduate advisor and predecessor paleontologist at The College of Wooster.
Richard Osgood, Jr., was born in Evanston, Illinois, in 1936. He went to Princeton for his undergraduate degree (I still remember his huge Princeton ring) and received his Ph.D. from the University of Cincinnati. He worked for Shell Oil Company in Houston just prior to joining the Wooster faculty in 1967. He was one of the pioneers of modern ichnology (the study of trace fossils), naming numerous new ichnotaxa and providing ingenious interpretations of them. At least one trace fossil was named after him: Rusophycus osgoodii Christopher, Stanley and Pickerill, 1998. Dr. Osgood died in 1981 in Wooster. He was an inspiration to me and many other Wooster geology students during his productive career, which was all too short.

References:

Osgood, R.G., Jr. 1970. Trace fossils of the Cincinnati area. Palaeontographica Americana 6: 281-444.

Schlotheim, E.F. von. 1820. Die Petrfactendunde auf ihrem jetzigen Standpunkte durch die Beshreibung seiner Sammlung versteinerter und fossiler Überreste des Thier- und Pflanzernreichs der Vorwelt erläutert 1-457.

Stanley, D.C.A. and Pickerill, R.K. 1998. Systematic ichnology of the Late Ordovician Georgian Bay Formation of southern Ontario, eastern Canada. Royal Ontario Museum Life Sciences Contribution 162, 56 pp., 13 pl. Toronto.

Wooster’s Fossils of the Week: Bivalve escape trace fossils (Devonian and Cretaceous)

January 29th, 2012

It is time again to dip into the wonderful world of trace fossils. These are tracks, trails, burrows and other evidence of organism behavior. The specimen above is an example. It is Lockeia James, 1879, from the Dakota Formation (Upper Cretaceous). These are traces attributed to infaunal (living within the sediment) bivalves trying to escape deeper burial by storm-deposited sediment. If you look closely, you can see thin horizontal lines made by the clams as they pushed upwards. These structures belong to a behavioral category called Fugichnia (from the Latin fug for “flee”). They are excellent evidence for … you guessed it … ancient storms.
The specimens above are also Lockeia, but from much older rocks (the Chagrin Shale, Upper Devonian of northeastern Ohio). Both slabs show the fossil traces preserved in reverse as sediment that filled the holes rather than the holes themselves. These are the bottoms of the sedimentary beds. We call this preservation, in our most excellent paleontological terminology, convex hyporelief. (Convex for sticking out; hyporelief for being on the underside of the bed.)

The traces we know as Lockeia are sometimes incorrectly referred to as Pelecypodichnus, but Lockeia has ichnotaxonomic priority (it was the earliest name). Maples and West (1989) sort that out for us.
Uriah Pierson James (1811-1889) named Lockeia. He was one of the great amateur Cincinnatian fossil collectors and chroniclers. In 1845, he guided the premier geologist of the time, Charles Lyell, through the Cincinnati hills examining the spectacular Ordovician fossils there. He was the father of Joseph Francis James (1857-1897), one of the early systematic ichnologists.

References:

James, U.P. 1879. The Paleontologist, No. 3. Privately published, Cincinnati, Ohio. p. 17-24.

Maples, C.G. and Ronald R. West, R.R. 1989. Lockeia, not Pelecypodichnus. Journal of Paleontology 63: 694-696.

Radley, J.D., Barker, M.J. and Munt, M.C. 1998. Bivalve trace fossils (Lockeia) from the Barnes High Sandstone (Wealden Group, Lower Cretaceous) of the Wessex Sub-basin, southern England. Cretaceous Research 19: 505-509.

Wooster’s Fossil of the Week: A stromatoporoid (Middle Devonian of central Ohio)

October 30th, 2011

Stromatoporoids are very common fossils in the Silurian and Devonian of Ohio and Indiana, especially in carbonate rocks like the Columbus Limestone (from which the above specimen was collected). Wooster geologists encountered them frequently on our Estonia expeditions in the last few years, and we worked with at least their functional equivalents in the Jurassic of Israel (Wilson et al., 2008).

For their abundance, though, stromatoporoids still are a bit mysterious. We know for sure that they were marine animals of some kind, and they formed reefs in clear, warm seas rich in calcium carbonate (DaSilva et al., 2011). Because of this tropical habit, early workers believed they were some kind of coral, but now most paleontologists believe they were sponges. Stromatoporoids appear in the Ordovician and are abundant into the Early Carboniferous. The group seems to disappear until the Mesozoic, when they again become common with the same form and life habits lasting until extinction in the Late Cretaceous (Stearn et al., 1999).

The typical stromatoporoid has a thick skeleton of calcite with horizontal laminae, vertical pillars, mounds on the upper surface called mamelons, and dendritic canals called astrorhizae shallowly inscribed on the mamelons. These astrorhizae are the key to deciphering what the stromatoproids. They are very similar to those on modern hard sponges called sclerosponges. Stromatoporoids appear to be a kind of sclerosponge with a few significant differences (like a calcitic instead of an aragonitic skeleton).

Stromatoporoid anatomy from Boardman et al. (1987).

Top surface of a stromatoporoid from the Columbus Limestone showing the mamelons.

There is considerable debate about whether the Paleozoic stromatoporoids are really ancestral to the Mesozoic versions. There may instead be some kind of evolutionary convergence between two groups of hard sponges. The arguments are usually at the microscopic level!

The stromatoporoids were originally named by Nicholson and Murie in 1878. This gives us a chance to introduce another 19th Century paleontologist whose name we often see on common fossil taxa: Henry Alleyne Nicholson (1844-1899). Nicholson was a biologist and geologist born in England and educated in Germany and Scotland. He was an accomplished writer, authoring several popular textbooks, and a spectacular artist of the natural world. Nicholson taught in many universities in Canada and Great Britain, finally ending his career as Regius Professor of Natural History at the University of Aberdeen.

Henry Alleyne Nicholson (1844-1899) from the University of Aberdeen museum website.

References:

Boardman, R.S., Cheetham, A.H. and Rowell, A.J. 1987. Fossil Invertebrates. Wiley Publishers. 728 pages.

DaSilva, A., Kershaw, S. and Boulvain, F. 2011. Stromatoporoid palaeoecology in the Frasnian (Upper Devonian) Belgian platform, and its applications in interpretation of carbonate platform environments. Palaeontology 54: 883–905.

Nicholson, H.A. and Murie, J. 1878. On the minute structure of Stromatopora and its allies. Linnean Society, Journal of Zoology 14: 187-246.

Stearn, C.W., Webby, B.D., Nestor, H. and Stock, C.W. 1999. Revised classification and terminology of Palaeozoic stromatoporoids. Acta Palaeontologica Polonica 44: 1-70.

Wilson, M.A., Feldman, H.R., Bowen, J.C. and Avni, Y. 2008. A new equatorial, very shallow marine sclerozoan fauna from the Middle Jurassic (late Callovian) of southern Israel. Palaeogeography, Palaeoclimatology, Palaeoecology 263: 24-29.

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