Mazon Creek concretion ID request

[digit]

Managed to stop in for a little Mazon Creek style Easter egg hunt when I was up in Chicago last June. Brought back maybe a gallon or so of concretions and I've been cycling them in my freezer (when I remember). I like to give them a bit of a (gentle) tap around the edges from time to time. This often helps the concretion to shed an outer layer or to coax a split that is nearly there and just begging to pop. As expected, I've had a number (the majority) of concretions open up to reveal a complete lack of anything at all within. The only thing that revealed itself to be of interest was this little concretion that measures 3.5 x 4.0 cm. I pulled out my copy of The Mazon Creek Fossil Fauna book and you think with that information at my fingertips that I'd be able to make a coherent guess as to the identity of this fossil but I am at a loss to match it up convincingly to any of the taxa described there. Hoping some of the members here with more experience can chime in.

 

@Nimravis

@RCFossils

@stats

@Mark Kmiecik

 

 

       

 

[TheRocksWillShoutHisGlory]

Do you know if it was from pit 11?

[fossilnut]

I have no idea what it is but at least to my eyes it is outstanding. Wonderfully centered and symmetrical. I will follow to have the mystery revealed. Congratulations on your find. Thanks for posting.

[TheRocksWillShoutHisGlory]

I'm leaning towards a coprolite, I think I'm seeing some bits of undigested material in the upper third in the lighter gray section. 

 

That would also explain why it wouldn't be in a flora book.

[digit]

6 minutes ago, TheRocksWillShoutHisGlory said:

Do you know if it was from pit 11?

Yes. It is Pit 11 (Essex fauna).

 

We spent most of our time poking around the Mazonia South Unit--in particular in the steeper sections around Ponderosa Lake. It our favorite place to hunt for concretions and collect ticks.

 

 

Cheers.

 

-Ken

[connorp]

Coprinoscolex maybe?

[Peat Burns]

Kind of has a sea cucumber texture to it (Achistrum)

[Mark Kmiecik]

I'm leaning toward coprolite, but at the same time wondering about that dark spike and what appears to be other protrusions at one end. Many MC fossils are "problematic".

 

Excellent photos, by the way!

[digit]

2 hours ago, TheRocksWillShoutHisGlory said:

I'm leaning towards a coprolite, ... That would also explain why it wouldn't be in a flora book.

Or a fauna book for that matter (I had meant to type Fauna).

 

2 hours ago, connorp said:

Coprinoscolex maybe?

I've considered this. The tail looks rather thin and pointed and the "head end" looks to be reflexed and bent backward.

 

1 hour ago, Peat Burns said:

Kind of has a sea cucumber texture to it (Achistrum)

I've considered this sea cucumber as well due to the texture but the ends on this specimen are more tapered than what seems to be normal for Achistrum.

 

I'm glad to see I've been down the same thought process as others. I ruled out an annelid due to the lack of segmentation and appendages and was left with some of the smooth worms like the echiurans and echinoids like holothorans.

 

While it is entirely possible it would be disappointing if this nicely contrasted item turns out to be nothing more than a coprolite. Let's see what other opinions this item generates.

 

 

Cheers.

 

-Ken

[Mark Kmiecik]

I don't see much in the way of setae, which are common to Coprinoscolex in most specimens, but that of course doesn't rule it out. This is what makes it "problematic". Unfortunately, the preservation of soft-bodied animals doesn't show as much detail as one would like.

 

EDIT: My apologies. The above statement regarding setae does not apply to Coprinoscolex. I confused it with another MC worm species and spoke without double-checking the information.

[digit]

That they are preserved at all is somewhat miraculous--although often highly enigmatic and open to interpretation.

 

 

Cheers.

 

-Ken

[RCFossils]

It is a pretty nice example of Coprinoscolex.

 

[digit]

Thanks. It is one of those cases of a concretion containing a fossil splitting really well on the fossil plane. Compared to some of our members who have buckets of Mazon Creek concretions, I have many fewer lottery tickets to score with but I'm happy when I do. At least I have buckets of micro-matrix and can find hundreds of fossils per day (though few are larger than a few millimeters).

 

 

Cheers.

 

-Ken

[stats]

My guess is a leech, or more correctly Coprinoscolex, as has been mentioned already.  It looks like it has some of the cracked texture at the top.

 

Cheers,

Rich

 

[caldigger]

5 hours ago, digit said:

Ponderosa Lake, Its our favorite place to hunt for concretions and collect ticks.

And probably not in that order either!