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A Trilobite From Utah


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#1 susUrsus

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Posted 16 June 2010 - 12:12 PM

Hi. I dug in the U-dig trilobite quarry in Utah twice in May during our vacation. This was my first digging of fossils. We had a good time although most of our bugs are small and incomplete.

One of the bug looked slim at fist glance, the quarry guide said it was the rare Alokistocare and this really made my day. Upon examination under a loupe, the specimen does not seem to have shells and the pygidium. The right pleural lobe is partial but the left genal spine seems to be there. It measures 1.5x1cm. The negative seems to be better defined.

I purchased a copy of "Some Middle Cambrian Fossils from Utah" and tried to follow the descriptions of the trilobites in Wheeler Shale that looked alike. The Alokistocare harrisi should have lots of pustules but mine is smooth (because the shell is missing?). The size of the genal spine (if that one in mine is not artifact) does not look right either. I tried to count the axial rings but the missing of pygidium made it difficult to do so. As the trilobite seems to be incomplete, I wonder if the slim look is due to the missing of right pleural lobe.

So do you think it is an Alokistocare or other common species such as an Elrathia kingi? I appreciate your advice! Many thanks!

Ka Shing
Hong Kong

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  • negpos.jpg
  • positive.jpg
  • negative.jpg


#2 jhw

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Posted 16 June 2010 - 02:16 PM

i.d. seems right. Alokistocare don't have much by way of a pygidium. I'd say you have the whole bug there, though kind of worn down. Nice!

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#3 ebrocklds

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Posted 16 June 2010 - 03:58 PM

Alokisticare is an outdated name. it is now refered to as altiocculus harrisi. although i don't belive that is what you have. there is an as of yet undescribed altiocculus sp. that has 7 fewer thoracic segment than A harrisi, but is still micropygus (small pygidum) your specimen looks as though it is still buried under a thn layer of rock. there is the chance that the spcimen is burried in such a way that it gives it the appearance on long and slender. i have had several do this to me. after prep they often turn ou to be a common elrathia kingi. without seeing it in person i can't be sure.

still a nice trilobite whatever it turns out to be.

Brock

#4 ebrocklds

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Posted 16 June 2010 - 04:00 PM

you may want to also look at the Bolaspidella genus. specifically Bolaspidella housensis, although yours may be just a bit to large.
look at westernta.com for reference pics

Brock

#5 PaleoRon

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Posted 16 June 2010 - 04:03 PM

Very nice find. I have gone on collecting trips for trilobites in the past but so far I have'nt found a complete trilobite, only trilo-heads and trilo-butts.

#6 susUrsus

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Posted 20 June 2010 - 10:51 AM

Thanks a lot for replies!
Ka Shing



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