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This rock has growth rings! What is it?


IFoundARock

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IFoundARock

I found this rock near Green River Utah, east of the San Rafael Swell. Can anyone help me identify it?20220224_103854.thumb.jpg.d66ef2dd5ef54b14a860c889abd2a224.jpg20220224_103931.thumb.jpg.1008215528fa43423f36d347b5cde3bf.jpg20220224_103946.thumb.jpg.e1e000865c5f58695f2d499efd30a160.jpg20220224_104025.thumb.jpg.05d50d03e34bd79f0ee9fbda9d792f7a.jpg20220224_104152.thumb.jpg.ebbcf1b8953b27d21b1c0e84477389f0.jpg20220224_104431.thumb.jpg.8c879eb75bd6086f9df19f43def24293.jpg20220224_104555.thumb.jpg.a5f36567d610b67b437e54f3ff9d872c.jpg20220224_104338.thumb.jpg.a66a4d741976288dcf06dea1d5376b6a.jpg20220224_104202.thumb.jpg.bbc2bf33dbf9a2c2360523fd3e703dba.jpg

 

 

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the photo with the 6cm ruler suggests coral... to me.  Anyone else?

 

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The small tubules make me think this is a chaetetid.

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Beautiful find!

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The overall look is not as angular as I'm used to seeing in tabulates. I think this does have a more of a spongy look.

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Mark Kmiecik
2 hours ago, Rockwood said:

The overall look is not as angular as I'm used to seeing in tabulates. I think this does have a more of a spongy look.

 

Yup, chaetetid.

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IFoundARock

Thank You very much everyone for the help identifying this fossil! After doing a little bit of research into Chaetetids, it seems that is what it is!

This was my first big fossil find so pretty excited to be able to identify it and learn more about what I found.

Thanks again, you all Rock!

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fifbrindacier
On 2/24/2022 at 8:09 PM, Al Dente said:

The small tubules make me think this is a chaetetid.

 

On 2/24/2022 at 10:32 PM, Rockwood said:

The overall look is not as angular as I'm used to seeing in tabulates. I think this does have a more of a spongy look.

I agree with that, it's a very nice specimen.

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On 2/24/2022 at 8:08 PM, jpc said:

the photo with the 6cm ruler suggests coral... to me.  Anyone else?

 

Most likely, as several members have already indicated, these are chaetetid type sponges. If it comes from primary or later than Eocene strata, it is the best possibility.
If it comes from Mesozoic or Paleogene strata (Paleocene-Eocene), it would not hurt to take into account the strange Scleractinian coral Ahrdorffia, its structures are very similar to chaetetid type sponges.

 

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IFoundARock

The more I am learning more about fossil sponges vs corals, the more questions I have.

I am looking more into if my fossil is a Chaetetid sponge or a tabulate coral, which both have similar features...

It is my understanding that how to tell the difference between a sponge with tabulae and a tubulate coral (since they are visually similar) is that the sponge has the presence of spicules where the coral does not. 

I read that the presence of spicules in a living representative of Cheatetids is what got them reclassified as sponges (they were previously classified as corals).  And that modern sponges are further classified by what type of spicules they have and their skeletal mineralogy. 

I also read that it difficult to classify Chaetetids due to "the lack of spicules in fossils and lack of original mineralogy"

So my question is, if there is a lack of spicules in fossils, and the presence of spicules is the main distinguishing feature between a sponge and a coral, then how would one tell the difference between a fossil sponge and a fossil coral (especially in the case of the fossil I found where there is the presence of tabulae)? How could I know if the fossil I found is a sponge with tabulae or a tabulate coral?       

(And is everything I have read and mentioned above factually accurate?)

 

Thanks for helping this newbie better understand the fossil world!

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IFoundARock
4 hours ago, oyo said:

Most likely, as several members have already indicated, these are chaetetid type sponges. If it comes from primary or later than Eocene strata, it is the best possibility.
If it comes from Mesozoic or Paleogene strata (Paleocene-Eocene), it would not hurt to take into account the strange Scleractinian coral Ahrdorffia, its structures are very similar to chaetetid type sponges.

 

Thanks Oyo for the suggestion. I found the fossil on the surface of a small dry canyon south of Green River Utah that has Jurassic - Cretaceous rock. This area is less than 10 miles from the San Rafael Swell Anticline which exposes layers from Paleozoic -Jurassic. I don't know if it is possible that it was transported from the Swell area or if it eroded from near where I found it. The exact spot sits on a fault with Morrison Formation /Jurassic layers and Dakota Sandstone & Mancos Shale /Cretaceous layers bordering each other, with the Green River cutting down through all of it. I'll have to do some more research into the area and see if I can find any evidence as to how the fossil ended up where I found it.

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DPS Ammonite
3 hours ago, IFoundARock said:

I am looking more into if my fossil is a Chaetetid sponge or a tabulate coral, which both have similar features...

It is my understanding that how to tell the difference between a sponge with tabulae and a tubulate coral (since they are visually similar) is that the sponge has the presence of spicules where the coral does not. 

I read that the presence of spicules in a living representative of Cheatetids is what got them reclassified as sponges (they were previously classified as corals).  And that modern sponges are further classified by what type of spicules they have and their skeletal mineralogy. 

I also read that it difficult to classify Chaetetids due to "the lack of spicules in fossils and lack of original mineralogy"

So my question is, if there is a lack of spicules in fossils, and the presence of spicules is the main distinguishing feature between a sponge and a coral, then how would one tell the difference between a fossil sponge and a fossil coral (especially in the case of the fossil I found where there is the presence of tabulae)? How could I know if the fossil I found is a sponge with tabulae or a tabulate coral?       

(And is everything I have read and mentioned above factually accurate?)


See if there are Pennsylvanian rocks nearby. Chaetetids/Chaetetes are common in Pennsylvanian rocks in Nevada, southern Utah and New Mexico. I find lots in the Naco Formation of central Arizona too.
 

I think that chaetetids have also thought to have been bryozoans. There is an encrusting bryozoan species in the Naco that looks similar: polygonal openings; narrow parallel tubes and tabulae. Since there are no visible spicules in any Pennsylvanian chaetetids that I have heard of, I wonder if they could be a coral or bryozoan. Convergent evolution of sponges, corals and bryozoans.

 

Show us on a map where it was found. Maybe we can find Pennsylvanian rocks nearby with a good geological map.

 

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19 hours ago, IFoundARock said:

The more I am learning more about fossil sponges vs corals, the more questions I have.

I am looking more into if my fossil is a Chaetetid sponge or a tabulate coral, which both have similar features...

It is my understanding that how to tell the difference between a sponge with tabulae and a tubulate coral (since they are visually similar) is that the sponge has the presence of spicules where the coral does not. 

I read that the presence of spicules in a living representative of Cheatetids is what got them reclassified as sponges (they were previously classified as corals).  And that modern sponges are further classified by what type of spicules they have and their skeletal mineralogy. 

I also read that it difficult to classify Chaetetids due to "the lack of spicules in fossils and lack of original mineralogy"

So my question is, if there is a lack of spicules in fossils, and the presence of spicules is the main distinguishing feature between a sponge and a coral, then how would one tell the difference between a fossil sponge and a fossil coral (especially in the case of the fossil I found where there is the presence of tabulae)? How could I know if the fossil I found is a sponge with tabulae or a tabulate coral?       

(And is everything I have read and mentioned above factually accurate?)

 

Thanks for helping this newbie better understand the fossil world!

 

17 hours ago, IFoundARock said:

Thanks Oyo for the suggestion. I found the fossil on the surface of a small dry canyon south of Green River Utah that has Jurassic - Cretaceous rock. This area is less than 10 miles from the San Rafael Swell Anticline which exposes layers from Paleozoic -Jurassic. I don't know if it is possible that it was transported from the Swell area or if it eroded from near where I found it. The exact spot sits on a fault with Morrison Formation /Jurassic layers and Dakota Sandstone & Mancos Shale /Cretaceous layers bordering each other, with the Green River cutting down through all of it. I'll have to do some more research into the area and see if I can find any evidence as to how the fossil ended up where I found it.

As you can see there are several candidates for your specimen.
Being clear about the stratigraphy of the collection area would help to eliminate possible candidates. If the strata are primary, it would eliminate Ahrdorffia, if they are Mesozoic, as you indicate, it would eliminate the tabulate coral. At least we would eliminate some candidate.
Even with everything I fear that it will be difficult to reach a consensus on this issue. These are materials that are difficult to identify without adequate preparations, thin sections or at least polished ones, unless they are exceptionally well preserved. Your specimen does not present a good superficial conservation.
I'm going to tell you a story with these type of material. I have an outcrop where there is a chaetetes-type sponge, Acanthochaetetes, and the Scleractinian coral Ahrdorffia. I identified the Acanthochaetetes early as they were very characteristic and had been described in the area. However, the Ahrdorffia corals were another matter, they looked like Acanthochaetetes and were not described in the area. No clue. I didn't realize what they were until I picked up a very well preserved specimen and taking macro pictures of it started to see the corallites of the coral. From there, a lot of library work until reaching the genus.
In both cases they are very small and very similar structures. I have ended up going through the outcrop with a pocket magnifying glass and even then, until I get home, clean and do macro photography, I am not usually sure what they are exactly. Sometimes, if the conservation is not good, even after this I don't know what they are.

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