Cricoconarids from Arkona

Cricoconarids are fossil tubes that look like tiny squid shells or pencil points. They are mysterious fossils that are hard to categorize and considered problematic. Right now they are considered to be worm tubes or possibly related to jellyfish or corals. I've found two types of these enigmatic fossils at Arkona.

The first is Styliolina fissurella which are usually so tiny that they are often overlooked. They are small (1-2mm) smooth shells that look like miniature Belemnites. The fossil below represents hundreds, possibly thousands of individual shells that were washed together, by currents likely, into a small shoal which then fossilized. It was found washed out from the Arkona formation.

The other is Tentaculites which is well known from the lower Paleozoic. I wrote about some chunks of matrix that I found a few months ago that were packed full of Tentaculite shells here. Tentaculites are larger than Styliolina fissurella and have regularly spaced, raised growth rings along the length of the shells. I found this paper on Tentaculites from Poland, while researching Styliolina, that even breaks them, down into species and shows a cross setion through the shell. This first picture shows two examples of individuals that were found in the Arkona formation (top) and Hungry Hollow member of the Widder formation (bottom).

It's easiest to find and recognize Tentaculites within the Arkona formation. Here they can be found commonly associated with Mucrospirifer arkonensis, Devonochonetes sp. and individual loose columnal sections from crinoids.