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Northern Sharks

Agnostid Triolobite

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Northern Sharks

This is one for Brock, but of course anyone can respond. I just got this slab from the mid-cambrian Wheeler Formation in Millard County Utah. It has several trilobites which were identified as Peronopsis interstricta. In my searching about this species, I don't see a lot of difference between this and several other species of Agnostids. Are the differences so picky that I just don't see them in photos? Also, I believe this photo shows the head at the top, is this correct? These trilobites had no eyes and this species has no spines, so it's tough to say whether it's coming or going. Thanks as always for your info.

post-77-1201828860_thumb.jpg

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Guest solius symbiosus
I don't see a lot of difference between this and several other species of Agnostids. Are the differences so picky that I just don't see them in photos?

Differentiation among the species is very complex. I've seen a few Ordovician Trilobites on reputable sites lately that have confused the genera.

Also, I believe this photo shows the head at the top, is this correct?

It looks like there is an occipital lobe posterior to the glabella. If so, then yes, the head is at the top of the photo.

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jkfoam

I always called this trilobite the"Studebaker" fossil because you couldn't tell the front from the back.

JKFoam

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ebrocklds

sorry for the delayed response, i am at the tucson show and have had little access to the web.

i am 95% certain that this is in fact a pernopsis interstricta. my reasoning is lame but i would say it is because of a few reasons.

first p. interstricta are very common in the wheeler and the others are quite rare. the other reason is that it has none of the identifying features visible to make it another type. the head is going up in the picture. if you look at the pygidium vs the cranidium you will notice that the tail has a compression fracture along the midline. the cephalon does not do this very often as it has 2 sutures on either side on the center that will release the compression stress. (i know this is not definitive but it is a quick way to get a good idea).

it looks ventrally preserved, so it could still have a spine on the first ring of the thorax or on the back of the glabella, if so it would be something else.

i would stick with p. interstricta

brock

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