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Hi everyone, 

 

We recently stumbled across this interesting specimen while combing through some rocks of the Verulam Formation (Upper Ordovician), just north of Manitoulin Island in Ontario. We initially thought trilobite, however we are now unsure, as there are over 30 segments of the thorax and they appear to be curved up towards the cephalon as opposed to down towards the pygidium. Any help is appreciated!

 

 

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Very neat piece! However, I'm leaning more toward orthocone nautiloid on this one. Let me tag one of our Verulam pros to give his opinion. @Northern Sharks

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Thanks Kane! We also thought the shape was more nautiloid but the size of the fossil (5¨width) is throwing us off a bit. 

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There's actually a monster-sized nautiloid in the Verulam. Endoceras proteiforme can reach several metres in length. :default_faint:Here are a few pieces I bumped into last autumn (nowhere near as robust as your piece!). 

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That's an even better match than Endoceras, for sure! The specimen of Gonioceras anceps pictured in Bill Hessin's book is not in the best of shape, but does seem to share that kind of "wraparound" look. The fact that it is inflated like this as opposed to crushed flat makes this a special find!

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FossilDAWG

It is indeed a nautilod, but not an Endoceras.  The way the camerae (chambers) curve forwards and then towards the back (which you can see clearly on the left side of the 2nd photo) is characteristic of the genus Gonioceras.  The species is likely Gonioceras anceps.  These nautiloids were flattened from top to bottom and lived on the sea floor, unlike some other nautiloids that were more active swimmers.

 

Don

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Thanks Kane and Fossil Dawg! Thanks for the information. Agreed, Gonioceras seems to be a likely culprit. We´re quite excited about this find :yay-smiley-1:

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Northern Sharks

Since I was tagged, but work got in the way, I'd also agree with a large nautiloid cephalopod, and Gonioceras looks like as good a fit as any.

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