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

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.


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.

About Mark Wilson

Mark Wilson is a Professor of Geology at The College of Wooster. He specializes in invertebrate paleontology, carbonate sedimentology, and stratigraphy. He also is an expert on pseudoscience, especially creationism.
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2 Responses to Wooster’s Fossil of the Week: A strophomenid brachiopod from the Middle Devonian of Michigan

  1. Paul Lefkowitz says:

    Although I am not involved professionally in geology, I love this website. It brings back many fond memories of my graduate work at Emory University (MS’70) in micropaleontology. My thesis was on a Cretaceousl foraminifera population study from an outcrop near Union Springs, Alabama.

    Thank you for the enjoyment you are bringing me.

  2. Mark Wilson says:

    Thanks, Paul! We’re glad you’re here. I did some work once in the Cretaceous of Alabama and enjoyed it very much. Good luck with your pursuits!

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