Wooster’s Fossils of the Week: “Star-rock” crinoids from the Middle Jurassic of Utah

Isocrinus_nicoleti_Encrinite_Mt_Carmel_585This little slab of crinoid stem fragments comes from the Co-op Creek Member of the Carmel Formation (Middle Jurassic) exposed in northwestern Kane County, Utah. I collected it with my friend Carol Tang as we explored a beautiful encrinite (a rock dominated by crinoid skeletal debris) exposed near Mount Carmel Junction. In 2000, Carol and her colleagues published a description and analysis of this unit and its characteristic crinoid, Isocrinus nicoleti (Desor, 1845). This piece sits on a shelf in my office because it is so ethereal with its star-shaped columnals (stem sections). In fact, the local people in the area collect pieces of the encrinite and sell them as “star rocks“. As I recall, some folks were rather territorial about the outcrops!

Isocrinus nicoleti is one of only three crinoid species known in the Jurassic of North America. (The others are I. wyomingensis and Seirocrinus subangularis.) Tang et al. (2000) showed that this species migrated into southwestern North America by moving southward through a very narrow seaway for thousands of kilometers. I. nicoleti had long stems and relatively small crowns, so it left us zillions of the columnals and very few calices. These washed into large subtidal dunes creating the cross-bedded encrinite.
Isocrinus asteriaThe genus Isocrinus is still alive, most notably in the deep waters around Barbados in the Caribbean. Above is a diagram of Isocrinus asteria originally published by Jean-Étienne Guettard in 1761. The long stem is star-shaped in cross-section.
Pierre Jean Edouard DesorThis gentleman is Professor Pierre Jean Édouard Desor (1811-1882), who named Isocrinus nicoleti in 1845. He is shown here 20 years later. Desor was a German-Swiss geologist who studied two very disparate subjects: glaciers and Jurassic echinoderms. He trained as a lawyer in Germany, but got caught up in the democratic German unity movement of 1832-1833 and had to flee to Paris. In 1837 he met Louis Agassiz and began to collaborate with him on a variety of projects paleontological and glaciological. He even had a trip to the United States where he helped survey the coast of Lake Superior. He took a position as professor of geology at the academy of Neuchâtel, Switzerland, in 1852, eventually retiring in genteel affluence. (This is not how these geological biographies usually end!)


Ausich, W.I. 1997. Regional encrinites: a vanished lithofacies. In: Brett, C.E. and Baird, G.C. (eds.): Paleontological Events, p. 509-519. Columbia University Press, New York.

Baumiller, T.K., Llewellyn, G., Messing, C.G. and Ausich, W.I. 1995. Taphonomy of isocrinid stalks: influence of decay and autotomy. Palaios 10: 87-95.

Desor, É. 1845 Résumé de ses études sur les crinoides fossilies de la Suisse. Bulletin de la Societe Neuchateloise des Sciences Naturelles 1: 211-222.

Hall, R.L. 1991. Seirocrinus subangularis (Miller, 1821), a Pliensbachian (Lower Jurassic) crinoid from the Fernie Formation, Alberta, Canada. Journal of Paleontology 65: 300-307.

Peterson, F. 1994. Sand dunes, sabkhas, streams, and shallow seas: Jurassic paleogeography in the southern part of the western interior basin. In: Caputo, M.V., Peterson, J.A. and Franczyk, K.J. (eds.): Mesozoic Systems of the Rocky Mountain Region, USA, p. 233-272. Rocky Mountain Section-SEPM, Denver, Colorado.

Tang, C.M., Bottjer, D.J. and Simms, M.J. 2000. Stalked crinoids from a Jurassic tidal deposit in western North America. Lethaia 33: 46-54.

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.
This entry was posted in Uncategorized and tagged , , , . Bookmark the permalink.

14 Responses to Wooster’s Fossils of the Week: “Star-rock” crinoids from the Middle Jurassic of Utah

  1. Howard Allen says:

    “Isocrinus nicoleti is one of only two crinoid species known in the Jurassic of North America. (The other is I. wyomingensis.)”

    Russell Hall (my palaeo prof at the University of Calgary) reported Seirocrinus subangularis (Miller) from the Jurassic of western Alberta. Did you miss this one, or has it been synonymized? I remember it well, because the specimen was on display in the U of C Earth Sciences building for years.

    Hall, R.L. 1991. Seirocrinus subangularis (Miller, 1821), a Pliensbachian (Lower Jurassic) crinoid from the Fernie Formation, Alberta, Canada
    Journal of Paleontology, v. 65, p. 300-307.

  2. Mark Wilson says:

    I missed it, Howard. Thanks for the correction and the reference! I will fix the entry.


  3. Jessica says:

    I have a rock that I found in the Buffalo National River. It has three yellow stars on it. Some people think it might be a crinoid fossil. I was wondering if you or someone you know could help me identify for sure if it is a crinoid.

  4. Mark Wilson says:

    Hello Jessica: You can send me images of that rock by email (mwilson-at-wooster.edu) and I will very happily try to identify the yellow stars. Best wishes, Mark Wilson

  5. Debbie says:

    I have star rocks that I find here in southern ut my parents started colleting them when I was a kid .I still go get them to this day .

  6. Mark Wilson says:

    Cool, Debbie. It is fun to know they are about 170 million years old!

  7. That is awesome I had no idea how old they were I’m still amazed at these fossilized star rocks I’m going to continue collecting them as long as I can .hopefully to leave this with my grandkids who will keep this going after I’m gone .

  8. Debbie says:

    Hey when I went and got my star rock last weekend and I got home sorting thew then I found a piece of Potter with the dirt we dug up that day if I send u a picture of it could u tell me if it would be the same age as my star rocks .I will send a pic of them as well .

  9. I don’t know how to send u the pictures though

  10. Mark Wilson says:

    You can send me images at mwilson-at-wooster.edu

  11. Debbie berry says:

    I have this rock I found and I’m not sure but it’s something can u tell me anything about it when I send u a picture. Thank u.

  12. Mark Wilson says:

    Hi Debbie: You can email photos of rocks or fossils anytime. Love to see them.

  13. Melisa Stuckey says:

    How do I send a picture of a rock in found on the bank of the Yazoo river with a star in the middle of a circle

  14. Mark Wilson says:

    Hi Melisa: You can email it to mwilson at wooster dot edu

Leave a Reply

Your email address will not be published. Required fields are marked *

This site uses Akismet to reduce spam. Learn how your comment data is processed.