Wooster’s Fossil of the Week: A mysterious sponge (Late Ordovician of Ohio)

I’ve been collecting and studying fossils from the Upper Ordovician of the Cincinnati region for three decades now, but I’ve never seen another specimen like the one pictured above. An amateur collector, Howard Freeland, generously donated this rock to Wooster late last year. He found it in Cincinnatian limestones cropping out in Brown County, Ohio.

At first Howard understandably thought he had found fish bones, which would be extraordinary for this age of rock and place of deposition. He took the slab to the Smithsonian Institution for identification by a vertebrate paleontologist. Not bones, was the answer, but they didn’t know how else to classify these finger-like fossils. When Howard showed them to me I suggested they were fossil sponges, and so here we are. I could be wrong so I hope the web community has some other ideas.

I believe these are sponge pieces because they were originally hollow (now they are filled with sediment), fibrous in structure, and had small holes irregularly preserved on their surfaces. They look in texture like the hexactinellid sponge Brachiospongia, but they do not have their distinctive thick extensions and radiating shape.

Small, irregular holes on fossil surface. They could be sponge incurrent pores. I would expect them to be more regular, though.

My search of the Ordovician sponge literature (what there is of it) has not turned up anything similar. I’ve gone to the usual websites for the Cincinnatian (like Steve Holland’s excellent Cincinnatian fossil catalog and the Dry Dredger’s webpages), but no luck.

Sometime during the existence of this webpage someone will come across these images and post their solution in the comments. I look forward to learning from them!


Carrera, M.G. and Rigby, J.K. 1999. Biogeography of Ordovician sponges. Journal of Paleontology 73: 26-37.

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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5 Responses to Wooster’s Fossil of the Week: A mysterious sponge (Late Ordovician of Ohio)

  1. Solius says:

    They are similar to degraded thanatocoenosic chaetids that I have seen in the Millersburg Mb of the Lexington???

    The “go to” Ord sponge guy is “Joe with a camera”. His blog:


  2. Mark Wilson says:

    Good idea, that it could be a chaetetid. I shall look further into this. Thanks!

  3. Dave says:

    Interesting article! I’ve found similar looking “stringy” looking fibers in a upper Silurian/lower Devonian rock formation called the Keyser here in PA. I posted about it on my blog at: http://viewsofthemahantango.blogspot.com/2011/12/possible-hexactinellid-sponge-from.html I’d be interested to learn if you have found any confirmation to what you have there. -Dave

  4. Mark Wilson says:

    Hello Dave! Our fossils are indeed very similar. Yours is a bit more disordered, though — maybe through some vagaries of preservation. I’m still puzzled about mine, and now yours! I think we’re on the right track with “sponge”. They may be hexactinellids or some types of chaetetids. Either way, it is much fun thinking about them! Thanks for your comment!

  5. Pingback: Wooster Geologists » Blog Archive » Wooster’s Fossil of the Week: A glass sponge from the Upper Ordovician of southern Ohio

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