Saturday, August 29, 2015

Agassizocrinus Floating Crinoid Calyx Fossil

These pictures are what appear to be dorsal calyx cups from an Agassizocrinus Troost 1850 (nomen nudum) Owen and Shumard 1852 fossil crinoid. The fossils were found in Glen Dean Member of Grayson County, Kentucky, USA. They date to Mississippian Period (Chesterian Stage).

I have been wanting to find this type of fossil for a while and finally got a chance to collect some. They are small about the size of a marble and are in a distinctive cup shape with five segments.

My friend Dave talks about them on his fossil blog in a 2013 posting. He cites the this reference for more information: Index Fossils of North America, Shimer and Shrock, 1944 Edition on pages 175-176, plate 61.

A more complete one can be seen on Crinus's fossil web site:

Images take with a Moto G 2nd Generation phone.

Above image of figures 6 and 7 of species undetermined of Agassizocrinus crinoid fossil. Image from A Critical Summary of Troost's Unpublished Manuscript on the Crinoids of Tennessee by Elvira Wood (1865-1928) 1909 Plate 7 Troost's Crinoids of Tennessee. Troost in his 1850 manuscript referred to this genus as Agassizocrinites.

I believed he named these fossils after Dr. Louis Agassiz who presented a list of fossil crinoids of Tennessee at a meeting of the American Association for the Advancement of Science on August 14, 1849. It was prelude to the publication of the fossils. Unfortunately, Dr. Troost died of cholera in 1850 four weeks after he sent the manuscript off the Smithsonian Institution for publication. It was not published till 1909 or 59 years later.