Utah's West Desert, Unusual Find

[Maxpedition]

This weekend we were out at a common site for hunting invertebrates, the Ibex - Fossil Mountain area, (near the Sevier Dry Lake Bed for Google Earth users).

We found lots of bivalves, and ammonoids, brachiopods, and even a few cone nautiloids as we worked our way up the mountainside.

On the way back down, we detoured away from the camp and a few hundred yards south into a shallow wash. Under a limestone ledge, in a bed of shale we found the following specimens. We sent a poor picture to the State Paleontologist of the major site find -which looks for all the world like a ribcage sticking out of the strata (!). He helpfully dismissed the photo as a nautiloid and sent us on our way. I'll attach that photo here at the end.

Now that we're home, and we have a few samples cleaned up, we want to share what else we found within a few feet of "the ribs."

Aside from these few samples, we left the site intact. We carefully covered the larger fossils to delay erosion and hopefully hide them from vandals. It is a remote area, but not exactly a secret.

Here is the first, I hope these pictures are suitable for identification.

Edited September 5, 2012 by Maxpedition

[Maxpedition]

The second sample, this is a pretty large rock, found just a few inches from the first.

[Maxpedition]

This is a great picture of the second find, along with the photo we sent the Paleontologist. In hindsight, it's not great. The "plate" is 12x12" sticking out of the shale, and there's another long fossil just above it that wasn't found before the camera died. Both are still undisturbed.

[Maxpedition]

And finally, we are sure this is a nautiloid. It was also found within a few feet of the others above.

This guy is far larger than any others we've found in that area.

We have plenty more pictures, also some good shots of the more common fossils from the Mountain.

We somehow managed to find a plate with several 2+ inch Trilobites on it, which is unusual.

[lordpiney]

They look like Baculites to me...not bones. they are very nice whatever they turn out to be.

[Auspex]

They are quite geodized, so I would not categorically rule out nautiloids, since the give-away structures may not be preserved.

[FossilDAWG]

Since the Ibex/Fossil Mountain area is entirely Paleozoic, and mostly Ordovician, Baculites would be most unexpected, sort of like a horse tooth in the same piece of limestone as a trilobite. Your specimens show no trace of ammonite type sutures, or the type of ribs that most Baculites species had.

Most of the Fossil Mountain cephalopods were straight-shelled orthocones with relatively large siphuncles. The siphuncle was a tube-like stricture that extended from the living chamber (the part of the shell actually occupied by the living animal) back through all the chambers of the phragmocone (the part of the shell made up of chambers separated by septa). In some Ordovician orthocones, such as the actinocerids, endocerids,and many micheliocerids, the siphuncle was the thickest and strongest part of the shell. In high energy environments, it was not uncommon for the shell to be totally fragmented except for the siphuncle. I suspect that is what you have with your specimens. The last couple of photos show the septa of an orthocone nautiloid, but it isn't clear to me if we are looking at the outside of the whole shell, in which case we would be seeing suture lines where the septa join the exterior shell, or if we are looking at a siphuncle of an endocerid nautiloid, in which case we are seeing the lines formed where septa join the siphuncle to form connecting rings. The other specimens don't show connecting rings and the lack of features will probably make them hard to ID.

Here's a photo of an Endoceras (from this web site) with the relevant structures labelled.

Don

[Maxpedition]

Thank you for that excellent explanation Don,

We really wanted a vert species, but knew it was just in the wrong place for it to be possible.

If it is indeed a orthocone nautiloid site, it is a tomb of epic proportion. There must be dozens this size laid about in just this 20' diameter area, victims of a huge collapse of some sort I assume.

I can attach more/better photos if you believe that any more would be necessary.

[ABeach]

Hi everyone! I am the other half of Maxpedition and this is another picture we took this weekend.

Edited September 5, 2012 by ABeach