Unknown Ordivician Trilobite

[piranha]

I don't know about anybody else, but I thought your specimen looked a lot like this one. Book claims that it is Amphilichas halli. Possibly Cincinnattian series - Upper Ordovician.

Thanks for the photo Andrea - you have a keen eye for trilobite features. A few of us initially had the same thought that as you - that it looked very much like a lichid pygidium. Thanks to Chris Gass we have a certain identification of this trilobite being the encrinurid Distyrax. Hopefully with a little elbow grease the stratigraphic origin can be squared with the Ordovician of Fossil Mountain. At a minimum it's the first known Distyrax collected in Utah. Stay tuned for additional updates ....

[davehunt]

Guys, I have some commitments over the next couple days that are keeping me from directing all my attention to providing the full set of photos, but I wanted to get something up for folks to look at. I took some photos, but I'm not happy with the result and I'm going to redo them, but here is one shot that provides a good mix of what I have from the same site. Please let me know if you'd like to see better shots of individual items.

I think B may be a crinoid stem, though it is not a clear shot.

I and J perhaps part of an Endocerid (I have another whole one in matrix, shot to come)

The hashplates are lots of C.

I don't know gastropods at all (A, D, E, F, G, H). Sorry, I will try to get better focus on those, but there is also not much detail.

You might also find this interesting. That's Fossil Mountain in the picture and they are referring to it as early/middle (not even Late) Ordivician (Juab Limestone and Kanosh Shale).

Thanks for your support and I'll be posting more in a couple days.

Dave

Edited December 12, 2010 by davehunt

[piranha]

Excellent associated fossil goodies Dave. When you take the new photos maybe a individual shot for each fossil might be a good idea. Too many objects of differing size and depth will always fool the auto-focus of digital cams. Still I'm very excited to see this preliminary group. Is this all of them or just a small sample? Once you get all of the the fossil escargot captured crisply we can impose on the gastropoda experts for possible classification. Thanks for posting Dave - have a great weekend!

[Ammonoid]

The rocks at Fossil Mt., Utah, are all early Middle Ordovician, Dapingian Stage. The Juab Limestone is assigned to the Rangerian Stage of the NA Regional units, and all formations above, up to the Eurreka Quartzite, are assigned to the unofficial "Kanoshian". The rocks below the Juab are all Early Ordovician and are the type locality for the Ibexian Series of NA usage. There are Late Ordovician and Silurian rocks in the area, but they are dark dolomites, and look nothing like the rock your trilobite is in. Good luck on getting an ID for the trilobite.

Edited December 12, 2010 by Ammonoid

[piranha]

On 12/12/2010 at 12:16 PM, Ammonoid said:

The rocks at Fossil Mt., Utah, are all early Middle Ordovician, Dapingian Stage. The Juab Limestone is assigned to the Rangerian Stage of the NA Regional units, and all formations above, up to the Watson Ranch Quartzite, are assigned to the unofficial "Kanoshian". The rocks below the Juab are all Early Ordovician and are the type locality for the Ibexian Series of NA usage. There are Late Ordovician and Silurian rocks in the area, but they are dark dolomites, and look nothing like the rock your trilobite is in. Good luck on getting an ID for the trilobite.

Thanks for the great information Ammonoid. We did get the ID on the trilobite from Chris Gass who formally described the genus and associated species. Now it's a matter of stratigraphic origin that we're trying to corroborate. It sounds like you're very familiar with Fossil Mountain and the surrounding formations. I'm very curious about the relationship of the Silurian horizon you reference. The appearance and color of the matrix could be the result of incorrect color temperature or post processing of the image. Silurian seems to be a easier conclusion. As it stands Distyrax has never been recorded from Utah. It might be a stretch that it's also a undescribed primitive Ordovician form.

[Ammonoid]

If you look at the top photo in post #22 of this thread, just above dave is a ridge with light gray on top and a dark band in the middle. The dark band is the top of the Silurian Laketown Dolomite, about 300 meters thick, or down to about the level of his head. The gray at the top is Devonian and below is Late Ordovician, down to the top of the Eureka Quartzite (behind the hill to the right). The only way a Silurian fossil could cross the valley between that ridge and fossil Mt. would be for someone to carry it.

The fossil below was found at the base of the Kanosh Shale which is about the base of Fossil Mt. There are many similar trilobites found on Fossil Mt.

[davehunt]

Thanks Ammonoid, I knew you would have authoritative knowledge of this area from reading your blog. Oddly, I couldn't remember what your Forum member name was (which is pretty dumb of me). Thanks for your input.

I'm hoping to get the photos out by tomorrow night - Wednesday at the very latest. And I don't have anything as cool as that picture!

Got a paper to write (working on another degree - archaeology) that is due soon on explaining the distributional relationships between Great Basin fluted points and stemmed points in the changing environment of the early Holocene and it is currently kicking my butt.

Dave

Edited December 13, 2010 by davehunt

[piranha]

The only way a Silurian fossil could cross the valley between that ridge and fossil Mt. would be for someone to carry it.

The fossil below was found at the base of the Kanosh Shale which is about the base of Fossil Mt. There are many similar trilobites found on Fossil Mt.

Thanks Ammonoid for helping out. Eventually we'll figure out the stratigraphic origin of this strange bug. At first glance the trilobite in your photo has a similar appearance. After orienting it to the same angle of Dave's pygidium however, it clearly does not match. The pygidial furrows and terminal axis have a completely different form. Dave's trilobite has narrow furrows and a elongate almost elliptical axis. The trilobite in your picture has distinctly broad furrows and a comparatively small triangular pygidial axis. Perhaps the most definitive difference is the array of pygidial spines in comparison to a smooth rounded posterior border terminating with two median spines. I'm sure you're 100% correct that those are common trilobites to find at Fossil Mountain. Distyrax on the other hand is not. With all due respect I think it's appropriate here to show great deference to Chris Gass for his authoritative scholarship on the subject and his unwavering classification of this trilobite. For those who remain skeptical I would recommend a reread of his comments on page one of this thread.

Edited December 13, 2010 by piranha

[ebrocklds]

after looking at the evidence provided by everyone i am still not convinced that this trilobite is Distyrax. if you look at the composite image you will notice several major differences between the two specimens. first eh axial rings on teh pygidium are completely different. the Distyrax has many tight rings that go all the way to the end of the pygidium. the unknown specimen only has 4 possibly 5 larger rings and a single large axial "segment" with dimples on either side.

also the plueral furrows are completely different as well. on Distyrax they go from big to small as you move down the tail. which is oposite on the other where the thickest pleural "segment" is the last one.

the pygidial spines found on the unidentified specimen are very clear and easily recognizable. niether of the Distyrax shows any evidence of pygidial spines.

laslty Distyrax has not been found in utah so it throws up another red flag.

the pygidia that ammonoid posted are common to find complete specimens are much less common. they are from Pseudocybele lemuri.

Brock

[Ammonoid]

I am not saying my trilobite is the exact same as Dave's, just similar, and there are many similar bugs from that locality. I also am not saying the fossil wasn't carried across the valley by someone or something. I may be able to help with his cephalopods (his "crinoid" is actually the phragmocone of an nautiloid) but I will leave the ID of the trilobite to others. Just trying to help with the geology and some of the local fauna.

[davehunt]

Ammonoid and/or Inyo:

You seem pretty familiar with Fossil Mtn. Can you tell what formation I'm standing at from the picture (and elevation = 6200')? I parked at the "campground" on the north side and just walked straight up until I got to that main vertical ledge you see in the image. Everything I found was in the talus right there.

Thanks for all your input. I promise pictures are coming. Dave

Edited December 13, 2010 by davehunt

[tracer]

my wife just came in teh room and ast me why smoke was coming out of my ears. told her i was reading sompin complicated.

[davehunt]

Here come the pictures.

First, the best shots I have of the subject fossil: FM-2010-01

The color in the first image is actually the truest color match.

Edited December 14, 2010 by davehunt

[davehunt]

The gastropods. I'll reiterate that all specimens were found in the same area.

FM-2010-02

FM-2010-03

FM-2010-04

FM-2010-05

FM-2010-06

FM-2010-07

Edited December 14, 2010 by davehunt

[davehunt]

The nautoloids

FM-2010-08a and FM-2010-08b

FM-2010-09 - Ammonoid previously suggested this may be a "phragmocone of an nautiloid"

FM-2010-10 - I'm thinking this is a Endocerid, but not certain.

Edited December 14, 2010 by davehunt

[davehunt]

The mollusks:

FM-2010-11

FM-2010-12

FM-2010-13

FM-2010-14

I have other hash plates similar to FM-2010-14, but I'm not going to catalog them at this time.

[davehunt]

In going through the collection, I realized I may have a second trilobite. I doubt it is the same species, but if it is obvious to you, please let me know if you know the species.

FM-2010-15

And a third!

FM-2010-16

Edited December 14, 2010 by davehunt

[JohnJ]

Fantastic photos, Dave.

[davehunt]

OK, first, I want to thank everyone for your invaluable input in this quest of identification. I really appreciate it and if we were all in Ibex by Fossil Mountain, I would buy everyone a beer. Alas, there are no longer buildings in Ibex (but there is a really great GeoCache there that explains the history of that little settlement if you are ever out there).

I added photos of the catalog of specimens collected on Sept 15 when I found this trilobite, although, at this point, I think that may be a bit superfluous. Of all things, I think we have securely established, at least among ourselves, the Ordivician nature of Fossil Mountain. Fossil comparisons will be icing on the cake.

I think we also have a good authority in Mssr. Gass in the Genus level identification of the fossil. For sure, my fossil is not an exact match with the photo of another Distyrax sample, which is exactly what we'd expect from an ancestral form, but it appears to be the best match so far and I bow to Mssr. Gass's classification.

I think we can drop the whole "traveling fossil/trilobite" line of discussion. I read this comment by Ammonoid to be sarcastic or facetious, not an actual suggestion of the solution. Reasonable doubt and the previously cited Occam's Razor needs to take effect. I also was not in any Silurian sites before or after collecting this specimen.

Going forward, I'd like to suggest a couple things:

1. I think I've added all the information I can at this point. It would be great if Forum members could help identify the remaining specimens (using the catalog ID (FM-2010-xx)).

2. If Chris Gass is interested in pursuing the classification of this trilobite, I would be willing to send him casts and all the info we have. Piranha, would you be willing to follow-up with Chris in that regard? If not Chris, maybe someone knows someone at the U of Utah who might be interested?

3. It would be great if those of you who are intimately familiar with the geology of Fossil Mountain (Inyo/Ammonoid) could point me at some scholarly journal articles that describe Fossil Mountain. I think Chris Gass, or any university faculty, would require such reference to confirm our claims of the nature of the geology.

Again, thanks for reading this far, and for all your help in this matter.

Dave

Edited December 15, 2010 by davehunt

[palaeopix]

I think consulting with Brian Chatterton is a great idea as he has specialized in Ordovician Trilobite faunas for thirty odd years and if he is unable to corroborate Chris Gass' observation about the specimen in question then I doubt anyone will be able to. That and the fact that Brian Chatterton is a recognized expert on members of the Family Encrinuridae.

I might also offer the observation that Chris Gass' secondary and tertiary authors (Greg Edgecombe and Lars Ramskold) are also highly acclaimed and capable paleontologists that have worked on encrinurids as well.

I personally welcome Dr. Chatterton's views on this topic whether they support or refute Chris' observation.

Dan

[Ammonoid]

http://pubs.usgs.gov...p1579/p1579.pdf

May help, it has a long list of references that may also help.

The Nautiloids: bottom and top are both endosiphocones from Endocerids, transverse and longitudinal sections required for ID, and there are still a lot of undescribed fossils out there so that might not prove fruitful. The one in the center photo can just be referred to an orthocone without the siphuncle shown for a better ID.

The goal of all paleontology is to match the fossils with the rocks and vice versa, I look forward to seeing how this one turns out.

[Guest N.AL.hunter]

All I can add is to watch out for that talcum-powder-like "sand" in some of the dry stream beds at the base of Fossil Mountain!! I got my two wheel drive truck in that stuff and it sank down like it was in quicksand. Took me two hours to get it out, which was two hours of fossil collecting time lost!!!

[Acryzona]

Just to add a different perspective on this discussion, there may be a straight-backed ostracod (I've circled in red) near the trilobite impression. Any chance of getting a closer photo of that area? Might lend a clue to the stratigraphy debate.

Edited December 17, 2010 by Acryzona

[davehunt]

How are these?

[Geodigger]

In going through the collection, I realized I may have a second trilobite. I doubt it is the same species, but if it is obvious to you, please let me know if you know the species.

FM-2010-15

And a third!

FM-2010-16

My first impression of the second specimen is that it may be a partial pygidium belonging to a member of the family Bathyuridae. As far as I know the family is restricted to the Ordovician. For comparison I have attached a pic of a specimen belonging to the genus Bathyurus from the Upper Ordovician Black River Group of Ontario, Canada. The family has a highly inflated axis on the pygidium which appears to be eroded on your specimen.