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Mediospirifer

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My husband and I collected a lot of hash plates from a field trip near Cinncinnati, OH last summer. We finally got around to getting the mud off and examining our finds, and noticed a small, nearly complete trilobite cephalon that is neither Isotelus nor Flexicalymene, both of which are the more commonly-found trilobites for the area. This was Waynesville Formation, Ordovician era.

Here's a photo throught the microscope. The cephalon is approximately 1 cm wide:

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My husband thinks this is a Ceraurus sp. I can see the resemblance to the pictures he found, but ours has two lobes on either side of the midline, while all of the pictures he found show three. I also think there are other subtle differences, so I'm hoping someone with more experience than us will weigh in. At the moment, what we have to go on for ID-ing the fossils we've found is the Dry Dredgers website list of what is known from this formation. There are several trilobites that can be found there, but Ceraurus is the closest to what we have.

Is this Ceraurus, or have we found something that isn't on the Dry Dredgers' list?

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Attached is a side by side comparison with Acidaspis cincinnatiensis which is recorded in the Waynesville Fm:

 

IMG1.jpg

 

Whittington, H.B. (1956)
Type and Other Species of Odontopleuridae (Trilobita).
Journal of Paleontology, 30(3):504-520
 
 
 

image.png.a84de26dad44fb03836a743755df237c.png

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That looks like it! :D

I see it is on the Dry Dredgers site. I guess Mr. Spirifer was thrown off by all of the spines on the complete specimen they show. It is difficult to focus only on the cephalon with that many appendages!

We have a second partial cephalon that might be the same species. There's probably more of the fossil hidden under the matrix, but I'm not going to try to uncover it! Not without some practice on other things first, anyway...

post-12648-0-07646500-1415991640_thumb.jpg

Same size as the first one, found at the same location.

Thanks to all! And Dinoboy123, yes, this was found not far from Cinncinnati.

I'd love to find a complete one!

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Nice find, Acidaspis is a lot rarer than Ceraurus in my experience.

In Ceraurus the glabella is parallel-sided, which gives it a squarish appearance instead of the triangular/tapered appearance of Acidaspis (and Flexicalymene). Also all the lobes are about the same size in Ceraurus, whereas in Acidaspis and Flexicalymene the glabellar lobe closest to the thorax is largest, and they decrease in size corresponding to the tapering width of the glabella as you go towards the anterior end.

Don

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Nice find, Acidaspis is a lot rarer than Ceraurus in my experience.

In Ceraurus the glabella is parallel-sided, which gives it a squarish appearance instead of the triangular/tapered appearance of Acidaspis (and Flexicalymene). Also all the lobes are about the same size in Ceraurus, whereas in Acidaspis and Flexicalymene the glabellar lobe closest to the thorax is largest, and they decrease in size corresponding to the tapering width of the glabella as you go towards the anterior end.

Don

Thanks, Don! It's good to know that we have a rarity. :D

I had noticed the different-sized lobes on our piece, as well as the shape of the anterior end of the glabella, and that both differed from the Ceraurus pictures we found. That was enough to make me want another opinion. :D I'm glad I posted it!

Truth be told, when I first looked at it, I thought it was a Flexi (and commented on that thought). Mr. Spirifer said "Let me see that" and picked up a loupe, then pointed out the knobbly surface. Not a Flexi with those bumps! Trilos are among his favorite fossils, and he's always hoping to find new ones. This will get a good place in our collection.

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