Unknown Ordivician Trilobite

[davehunt]

Can anyone ID this trilobite (I'm assuming it is the rear-half of a trilobite). It was found on Fossil Mountain in Utah which is a middle Ordivician site. The fossil is a cast and in the second photo is modeling clay that I pushed into the cast to hopefully present a better view.

I've cruised through several photo collections of Ordivician trilobites and found nothing like it.

Thanks!

[Auspex]

Good job with the modeling clay; one of our bug-people should be able to at least narrow it down from that.

[Caleb]

Very cool! My first thought was Lichid, but now I'm having my doubts. Hopefully we can find an answer for you. Nice find

(Edited because I'm not sure anymore )

Edited December 8, 2010 by Caleb

[piranha]

It looks like a Kainella sp.

Give me a moment and I'll post a photo.

[piranha]

My initial reaction to this bug was the same as Caleb. It really looks like a lichid tail but that's not possible. I've cross-referenced the treatise and the list of genera at WTA. Kainella is listed from a different formation of the Lower Ordovician of Colorado. The treatise is quite nondescript with regard to distribution because its known only from fragmentary individuals. If it's Kainella we must conclude it to have radiated through the Middle Ordovician. It's a very bizarre and rare trilobite for Utah - that's for sure. Great find Dave!

[Caleb]

Do you happen to know the formation name? That may help us narrow it down.

[davehunt]

Most of what I know about Fossil Mountain formations comes from this picture. Owner of ammonoid.com used to be a member here, not sure if he still is.

Fossil Mtn

This shot is from a ways away from the hill but I was just below the bulge on the right (and around back of it) which corresponds with Ow (Watson Ranch Quartzite) or high Ol (Lehman Formation).

Thanks! Dave

[Caleb]

Most of what I know about Fossil Mountain formations comes from this picture. Owner of ammonoid.com used to be a member here, not sure if he still is.

Fossil Mtn

This shot is from a ways away from the hill but I was just below the bulge on the right (and around back of it) which corresponds with Ow (Watson Ranch Quartzite) or high Ol (Lehman Formation).

Thanks! Dave

Thanks, I'll do some research into this tomorrow. Hopefully we can find an answer for you.

[piranha]

Do you happen to know the formation name? That may help us narrow it down.

Manitou Formation - Colorado

I found a few more occurrences from the Paleobiology Database HERE

There must be others in between just not listed or published online.

Deadwood Formation - Montana

Deadwood Formation - North Dakota

Goodwin Limestone Formation - Nevada

[davehunt]

This survey document talks about a Kainella zone near Ibex, which is only about a mile from Fossil Mtn (it is mostly just an old well and corral). If you Google Earth "ibex, ut", Fossil Mountain is directly to the west. And Skull Rock (also mentioned) is about 7 miles north. (page 21)

Kainella zone

The document also mentions a "fossil mountain" but it is one in NV not the UT one.

Still haven't seen a Kainella photo that exactly matches, however. The pygidium seems more like a single piece and immediate segments wrap the full length of the pygidium. There is also an interesting pattern on the pygidium. Almost like the design you might see on the thorax of a spider.

Edited December 8, 2010 by davehunt

[piranha]

On 12/7/2010 at 9:45 PM, davehunt said:

This survey document talks about a Kainella zone near Ibex, which is only about a mile from Fossil Mtn (it is mostly just an old well and corral). If you Google Earth "ibex, ut", Fossil Mountain is directly to the west. And Skull Rock (also mentioned) is about 7 miles north. (page 21)

Kainella zone

The document also mentions a "fossil mountain" but it is one in NV not the UT one.

Still haven't seen a Kainella photo that exactly matches, however. The pygidium seems more like a single piece and immediate segments wrap the full length of the pygidium. There is also an interesting pattern on the pygidium. Almost like the design you might see on the thorax of a spider.

Now I'm stumped as well - the photos I've come across are not a great match either. The figure from the treatise seems correct but it looks like contemporary scholarship will probably trump this info. What they were calling Kainella from circa 1950 must have undergone a revision or two in the last 60 years. I would pass this puzzler to the trilobite group at yahoo.

[davehunt]

How about this?

Pseudomera cf. P. barrandei Middle Ordivician

Maybe after losing the fringing sections. Literally looked at every picture on that site...

[piranha]

How about this?

Pseudomera cf. P. barrandei Middle Ordivician

Maybe after losing the fringing sections. Literally looked at every picture on that site...

I looked at all of them too! (twice )

The pygidial furrows are quite different ... that looks like a cold one.

I'll fast track it to the titans of taxonomy right now if you like.

[davehunt]

That would be great, thanks!

[piranha]

That would be great, thanks!

Done! I'll post it up there right now.

Hopefully someone will ID it quickly. I'll be back with the scoop soon.

Time to hit the hay - I'll be counting enrolled Phacops to fall asleep!

[Ordovician_Odyssey]

this is a tricky one, i've never seen it before(in the ordovician there were thousands of species of trilos......havent seen all yet ).....but your diffinatly correct, it is a pygidium(rear end).........i'll do a bit of research, see what that brings up.

[Ordovician_Odyssey]

maybe this?

[piranha]

On 12/8/2010 at 3:35 AM, trilobite guy said:

maybe this?

Modocia is definitely a Cambrian only trilobite. Unfortunately that website has provided incorrect info calling it Ordovician.

Good news is forthcoming however as I'm waiting for the OK to post the answer from someone who formally described a similar type from the Silurian of Illinois.

[piranha]

Kenneth C. Gass has responded:

 

Beyond sharing features with the encrinurids in general, this specimen has all of the diagnostic (and quite distinct) characteristics of the encrinurine Distyrax. The taxon that Gass et al. (1992) illustrated from Illinois is not the most typical species of this genus, and therefore is not the best species to compare with this specimen. The free ends of the fifth pair of pygidial ribs of the species that we illustrated completely merge and extend far behind the pygidial axis as a single, long spine. In this specimen, however, they are more typical of Distyrax. Specimens of Distyrax from the midwestern USA, Anticosti Island (Canada), Greenland and Europe are more similar. Distyrax is a very distinct genus, and this specimen is indistinguishable from it.

 

I therefore have little to no doubt that the pygidium that you posted belongs to Distyrax - however, it will be difficult to convince me that the specimen is Ordovician in age, as I am very cautious about data that I cannot verify personally or via unequivocally authoritative sources. That being said, I will not rule out that, based on the statement you made of its reported origin, a Late Ordovician age is possible, in which case this would be the earliest occurrence of Distyrax on record. The fact that the fifth rib tips do not quite unite behind the axis seems consistent with a primitive state.

 

Silurian Encrinurinae (Trilobita) from the central United States

Kenneth C. Gass, Gregory D. Edgecombe, Lars Ramskold, Donald G. Mikulic, and Rodney Watkins

[piranha]

With permission granted by the author Kenneth C. Gass:

Silurian Encrinurinae (Trilobita) from the central United States

Kenneth C. Gass, Gregory D. Edgecombe, Lars Ramskold, Donald G. Mikulic, and Rodney Watkins

Distyrax n.sp., testiferous specimens

Joliet Dolomite, Brandon Bridge Member

Romeo Quarry, Romeoville, Will Co., Illinois

[PaleoPastels]

There was actually another member who posted a trilobite he claimed to be from Utah in the Ordovician. Its neat there are actually more trilobites found in Utah besides Elrathia Thanks for sharing!

[davehunt]

Here is a start at establishing the location I found this trilobite. I found it on Sept 15, 2010. I collected it myself. It was the only trilobite I found. Upon review, I did find 3 trilobites, but only one of this variety.

The GPS location for the trilo is 38 52.654' N, 113 28.218' W, elevation 6200 feet. If you load that into Google Earth, turn the horizon out (so you're not looking straight down, but rather across the landscape) and spin the map so you are facing South, you will see the mountain and a dark band across the top third. I was directly below the dark band (the cliff is largely impassable at that location) on the north side of the hill. There is a great deal of talus there (potentially from several hundred feet above) and the trilo was in that talus.

This is me at the base of the band. Looking east towards Ibex.

Middle of freaking nowhere...looking north from up the hill.

As I mentioned, this is an Ordivician (488 - 433 mya) site. I've just confirmed this using the Utah geologic map available here - I used the one named "version 1".

I've included a clip from the map with a red X that approximates the location of Fossil Mountain. The map color indicates it is an Ordivician zone (also note the "O" in the zone color). If you set Google Earth back to "straight down view" and compare with the geological map, you'll see Fossil Mtn is in the Ordivician zone of the Confusion Range. It is easiest to find Sevier Lake first and work directly west from there (west side, bottom half).

I will try to add pictures of other items I found there. I don't have much as it was a long way over rough terrain back to the truck and I mostly just took a few hash plates and some snails that I liked. Not sure they will be particularly diagnostic.

Piranha, feel free to share with Gass, et. al.

Edited December 14, 2010 by davehunt

[palaeopix]

Great follow up on the location data!

So either you've found the earliest occurrence of Distyrax which Gass suggests may be a possibility or the maps are wrong which is also a possibility!

It would be very cool if you have found the earliest record of Distyrax!!

I do, however, know that if geological maps from Utah are like the ones up here in Western Canada (can't speak for Eastern Canada) then there could be some major discrepancies with the ages of rocks. I'm not saying that is the case but who knows how well the area was mapped.

Anyway I will follow this topic until we have a definitive answer on your beast and its age.

[piranha]

Excellent work Dave - we're getting warmer now. As we discussed previously the sum total of your account bolstered with a preponderance of verifiable field data and contemporaneously collected index fossils should help to make the case. A complete photo catalog of any associated fossils collected from that day will be extremely useful. (I'll be especially excited to see the gastropods) The moment these elements are presentable in a cogent and concise package I'll forward all of the data. The addition of your field notes and photos are like fresh paint on a canvas. Very exciting stuff Dave - great work and a greater find - BRAVO!

[lotsofpets]

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.

(The photo was taken out of Ohio Fossils copyright 1996 Columbus, OH)