Waccamaw Mystery Fossils

[ClearLake]

Can anyone tell me what these small items are.  They sort of look like little mushrooms with what seems to be a circular attachment type area and then an "upper" surface with very small dots or small bumps.  The grid is 5mm on a side so these things are about 2mm x 2mm.  These come from the Early Pleistocene aged Waccamaw Formation of North Carolina.  From the looks and color of them, they seem like they should be Echinoderm related, but I am just guessing.  I am not familiar with them and figured since I found quite a few of them, they must be something worth identifying.    Perhaps @sixgill pete or @Al Dente or any micro searchers may be able to set me straight.  Thanks for your help.

 

[minnbuckeye]

Not knowing if these exist in the Pleistocene, a type of button coral comes to mind. Just a guess from someone who probably shouldn't be guessing!!

 

Mike

[Tidgy's Dad]

Rolled spine bases of cidaroid echinoid test plates; I think. 

[Al Dente]

They are short spines from the regular urchin Arbacia. Arbacia have a mix of spine lengths.

[ClearLake]

5 hours ago, Tidgy's Dad said:

Rolled spine bases of cidaroid echinoid test plates

 

5 hours ago, Al Dente said:

They are short spines from the regular urchin Arbacia

Thank you both!  That has put me on the right track.  I just needed to flip them upside down in my head to see how they go.  They must go with the several dozen echinoid spines I also picked out of the matrix.  I'll do a little research and see if between the two I can narrow an ID down.  If not, that is fine.  Thanks for your suggestion too @minnbuckeye!!

[Coco]

10 hours ago, Al Dente said:

They are short spines from the regular urchin Arbacia. Arbacia have a mix of spine lengths.

I would be interested to see the different thorns of an Arbacia.

 

Coco

[caterpillar]

I disagree with some part of an echinid. As Mike say, I think it's coral

[GABRIEL.P]

It must be an Arbacia spine or a Bryozoan.

Edited December 14, 2020 by GABRIEL.P

[fifbrindacier]

I found that image of Arbacia :

[minnbuckeye]

16 hours ago, minnbuckeye said:

probably shouldn't be guessing!

 

 As I said!!! I also just noticed they are just 2 mm in length.

[Coco]

Yes Sophie, it is the reason why I told I would be interested in seeing the different spines of an Arbacia.

 

I have whole recent Arbacia punctulata in my collection and all ist spines are the same.

 

I only have Arbacia lixula tests, not whole ones, but it’s very close to A. puntulata.

 

Coco

[caterpillar]

I think I have found something interesting. Maybe Colobocentrotus spine

See on this link, page 20

http://dspace.mit.edu/bitstream/handle/1721.1/67360/765399844-MIT.pdf?sequence=2

[Coco]

It sounds like a very interesting document. I haven’t read it, but it seems to me that the images are very grown (close-up). I also have recent Colobocentrotus (Podophora) atratus (Linnaeus, 1758) in my collection and looked at under the binocular, the short spines are striated lengthwise and slightly grainy on the top, which surprises me a lot as I had never looked at them like that. To the eye they look smooth.

 

I would have thought those fossils didn’t belong to a sea urchin, but I think you found caterpillar, or else you’re close to the truth. There are two other species of Colobocentrotus but I don't have them...

 

Coco

[Al Dente]

Here are some Arbacia spines from my collection. These are from the Pliocene Yorktown Formation from the Lee Creek Mine. You can see the socket base on the spines that fit the ball-like tubercles on the urchin test.

 

 

[caterpillar]

I could be wrong but I don't think these little thorns belong to Arbacia. Did you find any in place on the test?

I think these are Colobocentrotus thorns that are found in the same deposit as Arbacia.

To my knowledge Arbacia only has long thorns

[Al Dente]

14 minutes ago, caterpillar said:

I could be wrong but I don't think these little thorns belong to Arbacia. Did you find any in place on the test?

I think these are Colobocentrotus thorns that are found in the same deposit as Arbacia.

To my knowledge Arbacia only has long thorns

Here’s a picture I pulled from Google of a modern Arbacia. There are only two regular Echinoids from the Yorktown Formation. They are Arbacia and Psammechinus. Only two regular echinoids from the Waccamaw Formation. They are Lytechinus and Arbacia. These short spines are found in the Yorktown, the Waccamaw and the James City Formations in North Carolina.

 

 

[ClearLake]

6 hours ago, caterpillar said:

As Mike say, I think it's coral

That is an interesting thought, and maybe if they were bigger, that might be something to look into.  But these are only about 2mm across, that would be on the small size of one corallite for many corals.  Button corals as was suggested I believe are only known from the Pennsylvanian and these are significantly younger.

 

2 hours ago, Al Dente said:

Here are some Arbacia spines from my collection. These are from the Pliocene Yorktown Formation from the Lee Creek Mine. You can see the socket base on the spines that fit the ball-like tubercles on the urchin test.

Thanks for the pictures, those do indeed look like the bases and the spines I found.

 

2 hours ago, Al Dente said:

Only two regular echinoids from the Waccamaw Formation. They are Lytechinus and Arbacia

Excellent, I was trying to track down what were my choices from the Waccamaw.  I also found an old post that showed about 4 species of Arbacia from that time period, but they look pretty similar so I'm not sure if the spines and/or bases are distinctive between the species.  I'll research a bit more, but will be very happy with  Arabacia sp. 

 

Thanks for all the input!

 

Mike

[caterpillar]

 

 

 

 

 

2 hours ago, Al Dente said:

Here’s a picture I pulled from Google of a modern Arbacia. There are only two regular Echinoids from the Yorktown Formation. They are Arbacia and Psammechinus. Only two regular echinoids from the Waccamaw Formation. They are Lytechinus and Arbacia. These short spines are found in the Yorktown, the Waccamaw and the James City Formations in North Carolina.

 

 

 

 

You may be right because you know the echinid fauna of this region better than I do. Arbacia thorns can be long or short but still cylindrical as seen in the photo you are showing. Here the spines are tabular with straight sides that appear to interlock with each other, as is the case with Colobocentrotus. There are only 2 regular echinoids in the Waccamaw Formation. Perhaps a third has not been described. If someone has a recent Colobocentrotus in collection it would be interesting to see the shape of the spines

 

 

[Al Dente]

I forgot about Eucidaris which has been reported from the Waccamaw Formation. I've never seen any pieces of that genus. Colobocentrotus is a Pacific genus adapted to strong tidal currents. In the Yorktown Formation where these small spines are found, the sediment is primarily sand but with some silt and clay indicating fairly calm conditions during deposition. Maybe the flat shape is an adaptation to shell crushing predators.

[ClearLake]

AHA!  I think I see the different viewpoints expressed here.  It was not obvious to me at first, maybe I am just slow.  @caterpillar is suggesting the fossils I originally showed are actual spines (from something like Colobocentrotus) whereas I was thinking they are the bases on the urchin test that the spine attaches to even though @Al Dente has said "short spines" several times.

 

What I was thinking is that the fossils I showed are the spine bases that are part of the urchin test (circled in picture below) and then the spines attach to that.  I have (finally??) convinced myself that indeed they are actual spines which is what  @Al Dente was also saying, but I wasn't hearing

 

 

The article that was linked indeed shows actual spines that do look somewhat akin to what I have.  Below are two figures I borrowed from that paper that show the nature of the short, broad, mushroom like spines (picture on the left) and a blow-up of one spine (picture on the right) in which you can see the microporous nature of the spine (which could be similar to what is seen in my specimens) as well as the little socket on the on the lower right of the picture where it attaches to the urchin test.

 

 

 

The Colobocentrotus is a recent genus from the Pacific (Hawaii) if I have read correctly so that seems unlikely, but the spines sure do look something like it.  My problem at the moment is that I have yet to find a published paper that describes spines such as what @Al Dente and I have shown (the smaller ones) actually attached to an Arbacia or the other genus reported from the Waccamaw.  The description of the genus Arbacia spines from the Natural History Museum (nhm.ac.uk) website: "Primary spines moderately long (usually a little less than the test diameter); ambital and adapical spines distally pointed, without cortex. oral spines ending in a small cap of glassy stereom (cortex)."  While maybe that description of the oral spines fits what I have found, I haven't found a picture or illustration to help me.  So, I'll just accept at the moment that I don't have definitive proof but realizing there are folks that have way more experience in this material than I do and maybe sometime I'll find the picture I'm looking for to associate these specifically to a given animal.  As always, with your help, I have learned a bunch of new things.  Thanks

 

Mike

[caterpillar]

I share your point of view. Until I see thorns like this in place on an Arbacia test, I won't be convinced. When I speak of Colobocentrotus, it is to give an idea about this kind of echinid. It can also be Heterocentrotus which also has flat spines and which appeared in the miocene. I think it is more on this side that we should look rather than on the Arbacia side

And if I can add something, Arbacia lives on rocky bottoms exposed to waves

 

 

 

 

 

 

 

[Coco]

Hi,

 

I looked at a current Arbacia punctulata from my collection with a binocular. The only difference between short and long spines is their size. I haven’t seen any other distinguishing features. Short spines may just be broken and eroded by waves and sand.

 

 

 

 

 

 

 

Coco

[Coco]

I did the same with Colobocentrotus (Podophora) atratus from Reunion Island.

 

 

 

 

Here we can slightly guess the fine granulation of the upper part

 

 

Here too

 

 

And the last pic ! the underside of a flat spine on the top of the sea urchin. You can see the ribbed sides. The overall shape is very similar to the OP fossils, assuming they are a little worn out. My spine is about 2 or 3 mm.

 

I have several copies of these small flat thorns. I can send them to someone qualified to get a more precise idea, it would be very interesting !

 

Coco

 

 

[Al Dente]

I did write someone who is very knowledgeable about echinoids, east coast echinoids in particular. He had not seen these before and said he agrees with others on this forum that they don't look like spines found on Arbacia. He did comment that Arbacia is the only urchin found in common from these formations.

 

I'm not convinced yet because the base of both the Arbacia long spines and the short spines in question are pretty much identical. They have the same ridged ornamentation. The ornamentation on Coco's Colobocentrotus is much finer than what is found on these spines. It would be unusual for these short spines to be from a new species of urchin when they are so common ( I find them every time I look through these formations for small fossils) but no test fragments from unknown species are found in these formations. 

[ClearLake]

@Coco, those are great pictures!  The purple urchin spines sure do look similar and as @Al Dente has found out present a bit of a quandary.  I also sent an inquiry off to an echinoid researcher and I'll let you know if he has any additional comments to add to the discussion.  It does indeed seem odd that if the spines in question belong to some other genus, why haven't tests been found, or even pieces.  I looked at the many test fragments I picked from the matrix, unfortunately I am not well versed enough in the differences to assign them to a specific genus, nor do I have a handy complete specimen to compare with.  I'll stare at them some more with pictures from the literature, but I doubt it will help much as @Al Dente has done this already with much more expertise and familiarity with the formations in question than I will ever have.  Very interesting!