St. Leon (IN) Trilobit

[Peat Burns]

I am hoping someone out there is extremely familiar with the surface texture of late Ordovician trilobites of the Cincinnatian.  I found this in St. Leon, Indiana.  I believe it is a trilobite glabella, and there might be a little bit more to expose.  Normally I wouldn't get excited about a trilobite fragment, but finding anything other than Isotelus or Flexicalymene at this site is a bit rare, and this could add a new taxon to my collection for that site.  Taxa that I thought might be candidates include:

* Ceraurus milleranus
* Amphilichas shideleri
* Tricopelta breviceps

 

Thanks for any help.

 

(scale is in mm)

[erose]

Try these web sites: http://strata.uga.edu/cincy/fauna/trilobita/trilobita.html and http://drydredgers.org/fragoth1.htm

 

I also get excited finding trilo bits that are not the "usual suspects."

 

Good find.

 

PS There have been some beautiful and complete specimens found at that cut other than Isotelus and Flexicalymene so keep your eyes wide open.

[piranha]

This is a partial Amphilichas cranidium.  There is a portion of the glabella, composite lateral lobe (cl), longitudinal (lf) occipital (of) furrows and the occipital ring.

 

[Peat Burns]

1 hour ago, erose said:

Try these web sites: http://strata.uga.edu/cincy/fauna/trilobita/trilobita.html and http://drydredgers.org/fragoth1.htm

 

I also get excited finding trilo bits that are not the "usual suspects."

 

Good find.

 

PS There have been some beautiful and complete specimens found at that cut other than Isotelus and Flexicalymene so keep your eyes wide open.

Thank you, erose.  I just can't get enough time on that cut.  I'd  like to just camp out there for a couple days... 4 hour trips here and there are just not enough to find the rare stuff that I know is hiding in there 

[Peat Burns]

26 minutes ago, piranha said:

This is a partial Amphilichas cranidium.  There is a portion of the glabella, composite lateral lobe (cl), longitudinal (lf) occipital (of) furrows and the occipital ring.

 

Thank you, piranha.  I was hoping you'd be lurking.  This is extremely helpful, as it gives me a better idea of the orientation.  I doubt if there is much more there posteriorly, but I'm going to peel back some of the matrix and find out nonetheless.

 

Thanks again.

[piranha]

Here is the original description of Amphilichas (=Acrolichas) shideleri 

 

Foerste, A.F. (1919)  LINK
Notes on Isotelus, Acrolichas, Calymene, and Encrinurus.
Bulletin of the Scientific Laboratories of Denison University, 19:65-81

 

 

There is very little published info on this species.

Dan Cooper did a brief description for MAPS 1986.

 

Cooper, Dan (1986) 
Cincinnatian Trilobites.

MAPS Digest, 9(4&5):24-32 

 

Amphilichas shideleri
Cranidium moderately convex; glabella broad and subrectangular; median lobe expanded anteriorly; basal area tending to become depressed; foremost pair of lateral glabellar furrows extended backward to form longitudinal furrows reaching occipital furrow; axial furrows diverted posteriorly; circumscribed occipital lobes present; occipital ring broad; preglabellar field absent; fixigenae subtriangular; palpebral lobes marked off by furrows; anterior sections of facial sutures converging forward, running parallel to axial furrows.  Thorax composed of 11 segments; axis broad; axial furrows shallow; pleurae horizontal and transverse proximally, bent downward and backward at fulcra.  Pygidium with axis extending whole of length and unfurrowed 3rd pleurae with single free points.

 

One of the rarest of Cincinnatian trilobites, even fragments of this species are extremely rare to find.  Only one complete specimen owned by the Smithsonian was known until Jeff Aubry, Bill White, Bob White, Steve Felton, David Cooper and myself made a co-sponsored dig producing 5 complete specimens.  4 of those specimens are now in the possession of the Cincinnati Museum of Natural History.

 

[Peat Burns]

@piranha, this is very informative. Thank you.  Do you have any ideas about why this species is so rare?  Do you think it was rare throughout the palaeoenvironment, or is it more likely a function of taphonomy?  Maybe a facies fossil?

[piranha]

Yes, wherever they are found, lichids are usually rare trilobites.  Evidently, this one is exceedingly rare.  Congrats! 

 

 

[Peat Burns]

1 hour ago, piranha said:

Yes, wherever they are found, lichids are usually rare trilobites.  Evidently, this one is exceedingly rare.  Congrats! 

 

 

Fascinating.   Thanks again for all the info.  I am very pleased with this find 

[fifbrindacier]

That's nice, i'm happy for you.

[piranha]

1 hour ago, Peat Burns said:

Fascinating.   Thanks again for all the info.  I am very pleased with this find 

 

 

Glad to assist!

 

If you find any others for comparison, here are a couple of Smithsonian specimens.  

 

[Peat Burns]

I removed the matrix from what is present of the cranidium.  Here is a "before", "after", and an overlay over the specimen photo that @piranha provided to show what is present and place it into context.  Thanks again! 

 

[westcoast]

Beautiful informative illustrative work.

[piranha]

On 5/7/2017 at 9:39 PM, Peat Burns said:

I removed the matrix from what is present of the cranidium.  Here is a "before", "after", and an overlay over the specimen photo that @piranha provided to show what is present and place it into context.  Thanks again! 

 

On 5/7/2017 at 11:13 PM, westcoast said:

Beautiful informative illustrative work.

 

As predicted lol... Elementary, my Dear Watson! 

 

[Malcolmt]

very very nice...... this bug is on my list of never having found a complete one, all I have are some bits and pieces

[Fossil Claw]

Not sure if it's the same species as the person you found. But I was extremely lucky in January of 2016 to win a partial amphilichas that is I would guess is about 3/4 complete insanely cheap on eBay for Mount Orab. Paid like $7.25 delivered. Seller probably was not to happy with that acution result.

 

 

[Peat Burns]

49 minutes ago, Fossil Claw said:

Not sure if it's the same species as the person you found. But I was extremely lucky in January of 2016 to win a partial amphilichas that is I would guess is about 3/4 complete insanely cheap on eBay for Mount Orab. Paid like $7.25 delivered. Seller probably was not to happy with that acution result.

 

 

Wow.  That was a good deal.  I think some people just like perfect, aesthetically pleasing fossils and don't want such partials.  Maybe that's why it went so cheaply.  The good news is that allows those of us who are students of palaeoecology and fossil assemblages to scarf them up!  Congrats on the nice score.

[Fossil-Hound]

@Peat Burns congratulations on the rare trilobite fragment.

[Peat Burns]

5 hours ago, Fossil-Hound said:

@Peat Burns congratulations on the rare trilobite fragment.

Thanks!