Missouri Fossil ID Help

[LoveRocks]

I found this fossil on a hiking trail near Eureka, Missouri. It was on top of a hill. There is a natural spring on the trail at the base of the hill. I think it is some kind of coral or sponge, but I can’t find any pictures that look exactly like this so I don’t know what it is. Any help you can give me is appreciated!

[Ludwigia]

I'm thinking sponge as well, but not at all certain. It might help if you could pinpoint the stratigraphy.

[Rockwood]

The growth pattern does give it the appearance of a sponge, but I think the individual shapes are that of a tabulate coral. 

[TqB]

It looks spot on for Chaetetes (a hypercalcified sponge, thought for a long time to be a tabulate coral).

[Rockwood]

25 minutes ago, TqB said:

It looks spot on for Chaetetes (a hypercalcified sponge, thought for a long time to be a tabulate coral).

Is the growth pattern/colony form the primary diagnostic ?

[TqB]

1 hour ago, Rockwood said:

Is the growth pattern/colony form the primary diagnostic ?

Not really, it often forms domes or sheets but so do plenty of corals. The main thing is the small tubes - I see a load of it in my local Mississippian, same age as much of St. Louis, and there isn't a similar Carboniferous tabulate.

 

 

[FossilNerd]

3 hours ago, TqB said:

It looks spot on for Chaetetes (a hypercalcified sponge, thought for a long time to be a tabulate coral).

I was thinking tabulate at first myself, but this does make sense. 

 

https://ucmp.berkeley.edu/porifera/chaetetids.html

[digit]

Welcome to the forum!

 

Very cool fossil. I'm glad it was something our members have knowledge of as it made for a fairly quick identification. Thanks for taking well lit and focused images (and with a scale too!) which helped to allow a quick ID.

 

 

Cheers.

 

-Ken

[LoveRocks]

Thank you everyone for your help!

[mrcircumspect]

Southwest Missouri has many forms of coral in the rock-record. Someone mentioned earlier in a comment that the geo-strata information would be helpful to further determine the nature of your find. I vote with those who think this to be some form of coral.  

[Rockwood]

5 hours ago, TqB said:

The main thing is the small tubes - I see a load of it in my local Mississippian, same age as much of St. Louis, and there isn't a similar Carboniferous tabulate.

I can't say that I clearly see the distinction in these photos, something that would be needed to definitively state that it is a Chaetetes, but in this circumstance I would not bet against this guy.

[TqB]

1 hour ago, Rockwood said:

I can't say that I clearly see the distinction in these photos, something that would be needed to definitively state that it is a Chaetetes, but in this circumstance I would not bet against this guy.

 Kind of you to say so! If it's Carboniferous (which seems most likely), then I'm pretty sure it's Chaetetes. If Ordovician, the field's more open - but it does look right for a chaetetid (and you do get Ordovician ones).

 

So the issue would then be: are chaetetids sponges or tabulate corals?

 

The critical difference from a coral is that chaetetids have spicules embedded in the skeleton, although they haven't actually been seen in them all. In ordinary views, they are technically practically impossible to distinguish from tabulates, right down to having tabulae, and it really comes down to the small tube size (typically less than 1mm, termed "calicles") for home  ID. 

To be honest, I've always been just a bit sceptical about the sponge assignation for some of them.  

 

Spicule pseudomorphs were first reported in UK Carboniferous Chaetetes here: spicule pseudomorphs in a new palaeozoic chaetetid

 

Here's one of mine, part silicified, 1mm scale bar.

 

And here's a figure from the original coelenterata Treatise (1956), when they were still thought to be corals (top two only are Chaetetes).

Same sort of size tubes (circa 0.5mm) as mine above.

 

[Rockwood]

I can imagine a tabulate that fed on dislocated sponge fragments and used the spicules as reinforcement bar.

But I'm a little strange that way. 

[Mark Kmiecik]

7 hours ago, LoveRocks said:

Thank you everyone for your help!

And thank you for reading the pinned topics about how to post an ID inquiry. As you can see, that gives the members who can ID it a bit of extra time so they can give additional information regarding your find. This way you also learn something more than just "it's a fossil".

 

Nice find by the way, and welcome to the forum. 

[TqB]

12 hours ago, Rockwood said:

I can imagine a tabulate that fed on dislocated sponge fragments and used the spicules as reinforcement bar.

But I'm a little strange that way. 

Sounds feasible! Some sponges incorporate foreign particles, including spicules from other species.

 

[FossilNerd]

I found chaetetids being classified as sponges instead of corals rather interesting. Was doing a little online research and came across this paper. Thought I'd share for anyone interested. Gives a history of the classification of chaetetids and then goes on to describe them in detail.

 

West, R. R. 2011. Part E, Revised, Volume 4, Chapter 2A: Introduction to the fossil hypercalcified chaetetid-type Porifera (Demospongiae). Treatise Online 20:1–79, 52 fig. © 2011, The University of Kansas, Paleontological Institute, ISSN 2153-4012

 

I tried to upload the PDF, but it's too large.

Here is a Link to the paper if anyone is interested.