Ordovician in Tennessee (Help!)

[Terri]

at least until D attaches them to the other critter she's inventing

...hmmm, a chephalobite..

 

[Terri]

Probably a genal spine with associated pleura...

I seem to be racking up quite a few trilobites for the Lebanon Limestone.

I posted the "round things" from post #333 over on TFF, one guy suggested possible nautiloid chambers, as you did at one point and then the conversation moved on to trilobites and the scarcity of, in the Nashville Dome, so I posted #87 from this thread and got some interesting info....

I think you found a very nifty ventral thoracic section of an Ordovician cheirurid (ceraurus-like) trilobite. The triangular pleural furrows, flanges and fulcral mechanisms are all consistent morphologically with this type of trilobite. The attached figures illustrate these features that are prominently preserved on your specimen. Note that the figures depict a top-through view to the ventral exoskeleton which is a slightly different aspect in comparison to your bottom-up example.

Thanks for posting!

 

[Terri]

Which led to this on the Lebanon Limestone....

Here is a relevant abstract of a paper/poster presentation for an upcoming GSA conference in October:

TRILOBITE BIOFACIES AND LITHOFACIES OF THE UPPER ORDOVICIAN (SANDBIAN) LEBANON LIMESTONE, NASHVILLE DOME, TENNESSEE

The Late Ordovician (Sandbian) Lebanon Limestone of central Tennessee is a succession of subtidal carbonates that includes abundant, storm-generated bioclastic pack-, grain- and rudstone. The large lepiditicopid arthropod, Eoleperdita, is a conspicuous component of the rudstone facies, with bedding surfaces commonly crowded with disarticulated valves. The associated trilobite fauna is moderately diverse, including six to seven species, and is dominated by encrinurids and cheirurids. In the latter respect, it resembles more diverse biofacies of the younger Pooleville Member of the Bromide Formation of Oklahoma. Although the Lebanon Limestone has been interpreted by previous workers as a single depositional sequence (M3), a distinctive, regionally correlatable, sharp-based, meter-scale interval of grainstone near the middle of the formation, suggests a more complex stratigraphy. This grainstone unit, often referred to as the "Massive Member", may represent a TST of a second sequence, and is in turn overlain by a significant flooding surface and the deepest subtidal facies of the Lebanon. This deeper facies includes cm-thick lime mudstone layers with basal accumulations of graptolite rhabdosomes, some of which are current aligned, suggesting an origin as distal tempestites. The sparse, associated trilobite fauna is limited to low diversity assemblages of isotelines. Eoleperdita is also common in the graptolitic lime mudstone facies, indicating a broader bathymetric range than is typical for leperditicopid arthropods. Restriction of the group to shallow subtidal and peritidal settings apparently occurred later in its history.

The id. and info. came from "Piranha"

 

[Terri]

ANYWAY...no luck yet on the "round things" from post #333, unless they are indeed nautiloid chambers...

 

[Architeuthoceras]

They are probably nautiloid chambers. They are just oriented in an unusual direction, If the surface of the rock was originally horizontal, the nautiloids would have been lying vertical in the mud, it is just kinda odd.

I'm glad you got your bug ID'ed.

 

[Terri]

it is just kinda odd.

I agree, just can't quite SEE it.

 

[Terri]

Here's another ceph/gastropod (I think). The last ceph in my photo stash until I'm able to get out again.

 

[Architeuthoceras]

Gastropod on the left, cephalopod on the right, crushed internal molds of each.

 

[Terri]

Thanks Kevin!

 

[Terri]

Could it be? Trace with trace maker? Or over active imagination? The depressions appear to have been made before the rock hardened and there seem to be drag marks between each depression leading right up to the shell and you can just see the edge of another depression just under the edge of the shell. What do you think Kevin?

 

[Architeuthoceras]

Could it be? It could be, but is it? If made by the brachiopod I would think it would have impressions of the ribs. The middle impression seems to be elongated toward the left, making the whole trace asymetric. This is a very intriguing trace fossil and I have no idea what made it, it will take some hypothesizing to determine.

 

[Terri]

Well, if the impressions were made in soft mud is it possible some of the detail was lost after they were made? I don't know a lot about brachiopods but they had pedicles that they used to attach to the sea floor, or at least some of them did? This is what I envisioned, the little fella somehow came loose from his moorings, couldn't quite get a good hold and continued attempting, dragging his pedicle between attempts....don't laugh (oh, go ahead) I tried!

 

[DWhatley]

it will take some hypothesizing to determine

Something smaller carrying off a live snail (because one bump looks like a snail sticking out of its shell) by picking it up and dropping it as it moves along (like ants do with a caterpiller)?

 

[Terri]

(because one bump looks like a snail sticking out of its shell

The bottom impression does have something in it, but even with a magnifying glass I can't make it out, almost tubular in shape, and it's (impression) deeper and more angled towards the end of the rock than the rest.

I would think it would have impressions of the ribs

I took a good look and the walls of the impressions are very smooth.

 

[DWhatley]

It is the fourth up from the bottom that makes me think of a snail (complete with antennae/feelers) trying to crawl away