Trilobite identification?

[NeilG]

It was suggested to me to post this also... As I had posted it in a previous thread... 

[NeilG]

Another angle

[Darktooth]

Do you have location/formation info? It helps with id. 

[NeilG]

Northeast Alabama and in sand stone.

[Darktooth]

I am not familiar with the trilobites from Alabama, but I am sure there are members who are.

[Fossildude19]

@FossilDAWG  @piranha 

 

Maybe Don or Scott will chime in.

[fifbrindacier]

OK, even if i'm quite sure to be out, i try an ID : i think it might be a Ptychopariida Alokistocaridae, and the kind maybe an Alokistocare.

[piranha]

I have shown this to colleagues familiar with Alabama trilobites.  

There are a few similar genera, but we have no consensus yet. 

Additional locality info could help narrow the list of possibilities.

 

 

 

 

[Fossildude19]

1 hour ago, piranha said:

I have shown this to colleagues familiar with Alabama trilobites.  

There are a few similar genera, but we have no consensus yet. 

Additional locality info could help narrow the list of possibilities.

 

Scott, 

According to this post of his, he is located somewhere close to Weiss Lake.

 

[FossilDAWG]

A possibility is Alokistocare americanum (Walcott 1916).  The large number of thoracic segments and tiny pygidium is consistent with that ID.  The species occurs in the Conasauga Shale at localities around Weiss Lake AL as well as in nearby Georgia.  Schwimmer (1989 Journal of Paleontology 63:484-494) redescribed the species and synonymized numerous species described by Resser.  The figure is from Resser 1938 and shows Acrocephalops nitida (20) and Acrocephalops insignis (28, 29), both species considered identical to Alokistocare americanum by Schwimmer.  One issue that has led to oversplitting of trilobite taxa in the Conasauga is type of preservation: trilobites can occur flattened in the shale, partially flattened on calcite cone-in-cone wafers (the same way Elrathia kingi is preserved in the Wheeler Shale), or fully three-dimensional on or in chert nodules.  Flattened shale specimens can have proportions significantly different from uncompressed chert specimens, and Resser was notorious for basing species on these sorts of taphonomic differences.

 

Don

[fifbrindacier]

9 hours ago, FossilDAWG said:

A possibility is Alokistocare americanum (Walcott 1916).  The large number of thoracic segments and tiny pygidium is consistent with that ID.  The species occurs in the Conasauga Shale at localities around Weiss Lake AL as well as in nearby Georgia.  Schwimmer (1989 Journal of Paleontology 63:484-494) redescribed the species and synonymized numerous species described by Resser.  The figure is from Resser 1938 and shows Acrocephalops nitida (20) and Acrocephalops insignis (28, 29), both species considered identical to Alokistocare americanum by Schwimmer.  One issue that has led to oversplitting of trilobite taxa in the Conasauga is type of preservation: trilobites can occur flattened in the shale, partially flattened on calcite cone-in-cone wafers (the same way Elrathia kingi is preserved in the Wheeler Shale), or fully three-dimensional on or in chert nodules.  Flattened shale specimens can have proportions significantly different from uncompressed chert specimens, and Resser was notorious for basing species on these sorts of taphonomic differences.

 

Don

Yes ! I'm glad because i see my tentative of ID wasn't so out of subject.

 

On 1 mars 2017 at 8:52 PM, fifbrindacier said:

OK, even if i'm quite sure to be out, i try an ID : i think it might be a Ptychopariida Alokistocaridae, and the kind maybe an Alokistocare.

 

[piranha]

I have already examined all of Resser's figures.  Unfortunately, none of them match well with the mystery trilobite.

The figures posted above have a distinctive prominent preglabellar field.  Also, they don't have long pleural spines.

 

Here is an improved version of the figures.

 

 

[piranha]

Here are Walcott's figures of Acrocephalites americanus (=Alokistocare americanum).

 

The wide preglabellar field is also quite evident in these figures.

 

Walcott, C.D. (1916)
Cambrian geology and paleontology III, Cambrian trilobites.
Smithsonian Miscellaneous Collections, 64(3):157-258

 

 

[FossilDAWG]

It's something of a head-scratcher.  I hope your contacts can come up with a better idea.

 

Unfortunately the geology around Weiss Lake is difficult to figure out.  The strata are highly inclined, indeed vertical in places, generally highly folded and faulted, and exposures are not great.  Bolaspidella zone fossils such as Elrathia antiquata occur in several places, but historical collections indicate other horizons up to and including the Aphelaspis zone are present.  Unfortunately the classic locality at Cedar Bluff is now buried under a bridge.  Also one can find trilobites from different zones in close proximity at some sites; it's unclear (to me anyway) if there has been winnowing and concentration of chert nodules from different zones into one layer, or if faulting has brought things into proximity.  Generally you are looking at nodules eroded from low outcrops of highly fragmented shale.

 

Don

[doushantuo]

walco

(just to enlarge upon Piranha's post)

NB: 42 Mb

[doushantuo]

A. is also mentioned in Mason (Cambrian of the Marble Mountains).Whitehouse,and

this one

[piranha]

43 minutes ago, FossilDAWG said:

It's something of a head-scratcher.  I hope your contacts can come up with a better idea...

 

 

Adding to the confusion is a lack of high-quality figured trilobites from the Cambrian of Alabama and Georgia.

David Schwimmer said ptychopariid for this trilobite and the one from the link Tim posted earlier in this thread.

 

 

 

[fifbrindacier]

It looks like an alokistocare idahoensis (file from the site : http://trilobites.naturalforum.net/)

 

 

[fifbrindacier]

And this one come from this site : http://collections.peabody.yale.edu/search/Record/YPM-IP-428836/Map

[piranha]

8 hours ago, fifbrindacier said:

It looks like an alokistocare idahoensis...

 

The photo you posted should be labeled Amecephalus (=Alokistocare) idahoense.  

The name is also incorrect at the link you posted to the Yale Peabody database.

 

Resser, C.E. (1939)
The Spence Shale and its Fauna.

Smithsonian Miscellaneous Collections, 97(12):1-29

 

 

As I mentioned above, the mystery trilobite is a ptychopariid but not Alokistocare.  

It does not match because Alokistocare has an obviously wide preglabellar field.  

 

Here is the definition from the Treatise on Invertebrate Paleontology:

preglabellar field: portion of cranidium lying between front of glabella and anterior border furrow.

 

The attached side by side comparison clearly shows a narrow preglabellar field for the mystery trilobite.

 

[fifbrindacier]

@piranha, i'll follow narrowly this thread because i'm very curious about this specimen.

[fifbrindacier]

You might find this site interesting : http://www.westerntrilobites.com/index.html

[Coco]

Fif, I let it be said to you to Hervé that he has to change the name of his trilobite ! (Your 1st photo)

 

Coco

[fifbrindacier]

2 hours ago, Coco said:

Fif, I let it be said to you to Hervé that he has to change the name of his trilobite ! (Your 1st photo)

 

Coco

Thanks, in fact he did had changed it but i took the old file instead of the new.

[Coco]

Hi,

 

OK Fifi, I understand that you hadn't updated your index cards before giving us it !

 

Coco