Fossil From Arkansas

[Roz]

This fossil pic was sent to me on my AR fossil site

for an ID and I don't know what it is.

It was found in Newton County, Arkansas

Does anyone know?

It is the only pic he sent so cropped it more to show the target fossil better.

[Nicholas]

Cross section of a crinoid holdfast?

[Hawkeye]

Ah, I've seen one of those on E-bay! It's one of those famous fossilized duck feet.

[tracer]

it's a print from an arkanpaw.

[RJB]

I have no idea what it is Roz, but it doesnt strike me as a fossil in any way.

RB

[Frank Menser]

Definitely a fossil. That looks like part of a shell, though of what I don't know. I have seen similar fragments in Florida.

[Roz]

Thanks all. Will ask for more pics as I don't think it is a cross section of a crinoid holdfast

but I could be wrong. I think that area of AR is Penn.

Looks like a shell to me also....

[jkfoam]

Roz,

I am not familiar wih the geology of newton County, AR, but the photo shows, in the upper right corner, what appears to be an impression of a crinoid columnal so that gives a clue to age. The object of interest appears to me to be broken in half showing us a cross section. And the remaining form does not resemble any invertebrate form that I am familiar with. I think Nicholas's suggestion of a holdfast fragment is as good a suggestion as any.

Menser, suggested a shell fragment. I think he was alluding to the exagerateted digitation of the outter lip of a snail like Aporrhais sp. but i don't think that matches the geologic age.

JKFoam

[Xiphactinus]

This is the internal mold of a crinoid. We commonly find these in the chert in the Burlington fm. If I had to bet, I would say it is a type of Physetocrinus.

[Frank Menser]

Menser, suggested a shell fragment. I think he was alluding to the exagerateted digitation of the outter lip of a snail like Aporrhais sp. but i don't think that matches the geologic age.

JKFoam

I'll be the first to say I am not an expert on Mollusks or for that matter Crinoids. But here is what I saw that I based my opinion on.

First, That is not an impression, as it stands partially clear of the limestone it is locked in and it is not composed of the same material as the rock it's in. Second, the blue color is consistent with millions of shell fragments I have seen in Florida, where by the way, that very porus limestone it's sitting in is common. My thought is that It looks very much like the inside view of a bivalve, possibly a fragment of a Scallop type shell. But again, I can easily be wrong

[Xiphactinus]

Menser, suggested a shell fragment. I think he was alluding to the exagerateted digitation of the outter lip of a snail like Aporrhais sp. but i don't think that matches the geologic age.

JKFoam

I'll be the first to say I am not an expert on Mollusks or for that matter Crinoids. But here is what I saw that I based my opinion on.

First, That is not an impression, as it stands partially clear of the limestone it is locked in and it is not composed of the same material as the rock it's in. Second, the blue color is consistent with millions of shell fragments I have seen in Florida, where by the way, that very porus limestone it's sitting in is common. My thought is that It looks very much like the inside view of a bivalve, possibly a fragment of a Scallop type shell. But again, I can easily be wrong

The rock really isn't porous -- all those holes are impressions from crinoid column segments! The chert in the Burlington limestone is litterally filled with voids created from dissolved crinoids and brachiopods. You can get some really cool internal structure fossils.

[Nicholas]

Roz,

I am not familiar wih the geology of newton County, AR, but the photo shows, in the upper right corner, what appears to be an impression of a crinoid columnal so that gives a clue to age. The object of interest appears to me to be broken in half showing us a cross section. And the remaining form does not resemble any invertebrate form that I am familiar with. I think Nicholas's suggestion of a holdfast fragment is as good a suggestion as any.

That impression is what got me thinking Crinoid

[jkfoam]

Menser, suggested a shell fragment. I think he was alluding to the exagerateted digitation of the outter lip of a snail like Aporrhais sp. but i don't think that matches the geologic age.

JKFoam

I'll be the first to say I am not an expert on Mollusks or for that matter Crinoids. But here is what I saw that I based my opinion on.

First, That is not an impression, as it stands partially clear of the limestone it is locked in and it is not composed of the same material as the rock it's in. Second, the blue color is consistent with millions of shell fragments I have seen in Florida, where by the way, that very porus limestone it's sitting in is common. My thought is that It looks very much like the inside view of a bivalve, possibly a fragment of a Scallop type shell. But again, I can easily be wrong

Frank,

I thought you meant the triangular shape of the object was similiar to the outer lip of some snails such as Aporrhais sp.

I stand corrected. I have got to quit alluding (LOL).

JKFoam

[MB]

It looks Batman

[Frank Menser]

The rock really isn't porous -- all those holes are impressions from crinoid column segments! The chert in the Burlington limestone is litterally filled with voids created from dissolved crinoids and brachiopods. You can get some really cool internal structure fossils.

Have to disagree. Crinoid sections have a very recogniseable structure which if you look at those "pores" they do not as far as I can see. The holes are irregular in shape and size. In S. Florida there are no crinoids, but the same looking kind of rock. I have seen very porus rock associated with Chert nodules in the Gainesville, FL area, the association was with echnoid fossils-but not Crinoids.

One way to confirm this as either Chert or Limestone is to do a hardness test on the rock. Chert is a form of Quartz which has a hardness of 7 on Moh's scale. Limestone is much softer (unless there are quartz grains included) but should be scratchable by window glass.

[Frank Menser]

Frank,

I thought you meant the triangular shape of the object was similiar to the outer lip of some snails such as Aporrhais sp.

I stand corrected. I have got to quit alluding (LOL).

JKFoam

Didn't even know that existed... Very cool!

[Xiphactinus]

Have to disagree. Crinoid sections have a very recogniseable structure which if you look at those "pores" they do not as far as I can see. The holes are irregular in shape and size. In S. Florida there are no crinoids, but the same looking kind of rock. I have seen very porus rock associated with Chert nodules in the Gainesville, FL area, the association was with echnoid fossils-but not Crinoids.

One way to confirm this as either Chert or Limestone is to do a hardness test on the rock. Chert is a form of Quartz which has a hardness of 7 on Moh's scale. Limestone is much softer (unless there are quartz grains included) but should be scratchable by window glass.

Frank - I'm very familiar with the rocks from that area in Arkansas. It's Mississippian - nothing at all like the rocks in Florida. The Burlington chert looks just like this example. If you look to the left of the left-most "lobe", you'll see a small section of criniod stem. At the end of each "lobe" - you see a small split. Each of these would lead to the attachments for an arm.

I don't have a good picture here at work, but note the split for two arms at each attachment point.

[Frank Menser]

Frank - I'm very familiar with the rocks from that area in Arkansas. It's Mississippian - nothing at all like the rocks in Florida. The Burlington chert looks just like this example. If you look to the left of the left-most "lobe", you'll see a small section of criniod stem. At the end of each "lobe" - you see a small split. Each of these would lead to the attachments for an arm.

I don't have a good picture here at work, but note the split for two arms at each attachment point.

I can see where you are getting at with the crinoid. There is a definite similarity.

As to the limestone/chert?. I would have to see a better detailed closeup before I change my mind on that. Almost forty years of collecting in Florida has made me very familiar with the types of rock found there. It does not look at all to me like the rock your crinoid is sitting in. Nothing is as ancient as Mississipian in the entire state, however, rock with that structure is not limited to any particular era.

Now you have me looking in my old boxes to se if I brought some of the rock I'm talking about up from Florida. The problem with common rock is you don't keep it and then suddenly, when you are hundreds of miles away...

[Roz]

Xiphactinus, with that pic I see exactly where you mean.

Thanks!