Cracked Shell Of What?

[Bev]

Ordovician

Either Maquoeketa or Decorah Shale

SE Minnesota

The shell is preserved, but is all cracked up and the shape is unknown to me. Thoughts???

For Scale

Closeup

Thanks for looking!

[Bullsnake]

I'm thinking mineral deposit, Bev. I don't see anything diagnostic either.

I may be (hopefully) wrong!

You might have to see what's underneath with a little prepping.

Cool looking, though.

[Bev]

I took pictures of the edges to show you why I think it is preserved shell, besides the feel of it which I can't show.

[Tethys]

I think its a large ostracod. Ostracoda of the

Dubuque and Maquoketa Formations

of Minnesota and Northern Iowa.

[Auspex]

I think its a large ostracod. Ostracoda of the

Dubuque and Maquoketa Formations

of Minnesota and Northern Iowa.

At 25 - 30 mm, it would be a humdinger!

[Tethys]

At 25 - 30 mm, it would be a humdinger!

True, most ostracods are less than 1mm. There is a tiny pyrite replaced example in Bev's other post. However, there are mid-Ordovician species that are much larger such as Leperditia fabulites. I am visually estimating this one at about 15 to 18 mm crushed flat. It is at an angle to the scale so it is hard to judge the dimensions.

[Bev]

So, I found an old large squashed shrimp? Cool!

[Auspex]

So, I found an old large squashed shrimp? Cool!

It is one suggested possibility.

[Bev]

Thanks Tethys! Appreciate any opinions!

[Tethys]

I found the source of many of the images in my field guide. It is available at project Gutenberg. Ancient Life - History of the Earth by H.A. Nicholson Here is the image for Lower "Silurian" Crustaceans which are actually Ordovician in age. Your fossil resembles i. Leperditia canadensis in shape, and size. Lower Silurian Crustaceans. a, Asaphus tyrannus, Upper Llandeilo; b. Ogygia Buchii, Upper Llandeilo; c, Trinucleus concentricus, Caradoc; d, Caryocaris Wrightii, Arenig (Skiddaw Slates); e, Beyrichia complicata, natural size and enlarged, Upper Llandeilo and Caradoc; f, Primitia strangulata, Caradoc: g. Head-shield of Calymene Blumenbachii, var. brevicapitata, Caradoc; h, Head-shield of Triarthrus Becki (Utica Slates), United States: i, Shield of Leperditia Canadensis, var. Josephiana, of the natural size, Trenton Limestone, Canada; j, The same, viewed from the front.

Most of these, [ostracods] are very small, varying from the size of a pin head to that of a hemp seed; but they are sometimes as large as a small bean.

I am guessing that since Mr. Nicholson was an englishman, he is referring to something like fava beans, broad beans or butter beans.