Crosswicks Creek NJ Paleocene brachiopod ID

[frankh8147]

Hello!

 

I found this Oleneothyris brachiopod (on left) in the Paleocene of New Jersey and noticed that it differed from my other Oleneothyris' from this site (on the left is a 'normal' shaped one that I find here). I read there was a less common brachiopod here called Oleneothyris fragilis  which seems to fit the description but i couldn't find any pictures of it online so I wanted to know what everyone thought. Below is a description I found online.

http://digitallibrary.amnh.org/handle/2246/2019

[non-remanié]

Correct! Very nice

[Tidgy's Dad]

i don't think it is Oleneothyris fragiis. 

Here is a thread I found on the matter; 

 

[Al Dente]

I'm confused as to whether Oleneothyris fragilis is a valid species. Howard Feldman published two papers in 1977 on Oleneothyris from the Hornerstown Formation. In one paper he argued that O. fragilis was too similar to O. harlani to be a subspecies much less a separate species (Paleoecology and variation of Oleneothyris harlani). In the other paper he concluded they were distinct species (Notes and descriptions of Oleneothyris fragilis). Here's a plate from the second paper.

[non-remanié]

It might have been easier if Feldman didn't publish both papers in the same year, but lets stick with his later, more informed opinion!  I haven't consulted Feldman's first paper (paleoecology and variation...) in a while but everything in the second paper (notes and descriptions of o. fragilis) is accurate.  Fragilis is smaller and seems to be spatially restricted to a small community.

 

Al Dente, have you seen any oleneothyris specimens from different states as obviously different as the fragilis plate you posted and Frank's specimen?   Fragilis clearly is something real.  The differences are quite apparent.  Perhaps its more likely a subspecies or variety, but that's a fine point of argument.  I think few people have used fragilis simply because it is extremely more rare than typical harlani and they have not encountered it.

[Al Dente]

I haven't seen O. fragilis in North Carolina but we have an Eocene brachiopod, Plicatoria wilmingtonensis, that is highly variable. It can be smooth or have many deep folds. Here is a picture from NC Fossil Club Fossil book volume 1, invertebrates.

[non-remanié]

A very common Eocene NC brachiopod.  Are smooth and folded both equally just as common and widespread?  I have quite a few from just a couple trips to CH many years ago IIRC.   I think the real question then is whether this sort of variability is meaningful or not.  What's the argument that both varieties smooth and folded are the exact same species other than them being both very common,  occurring together, and otherwise identical?   Are there modern analogs to consider?   I don't know the answers but all I can say is that the NJ fragilis are a very restricted small community, likely both in time and space, from all that I can tell.  The vast majority of the Oleneothyris biostrome is 100% typical harlani.  But in the fragilis community, most are fragilis.    

 

  

[frankh8147]

Interesting!

The spot I found this is right on the K-T boundary; do you think it could possibly be an earlier form of O. harlani? From my research, these specimens look to be in one location which is the beginning of the Eocene..

 

By the way, thanks so much for the research! This is a fun one!

[non-remanié]

12 minutes ago, frankh8147 said:

Interesting!

The spot I found this is right on the K-T boundary; do you think it could possibly be an earlier form of O. harlani? From my research, these specimens look to be in one location which is the beginning of the Eocene..

 

By the way, thanks so much for the research! This is a fun one!

Its "fragilis".  Whether fragilis is a distinct species, subspecies or variety is the real question.  Actually, the site is not on the KT boundary. It is at the boundary of the Hornerstown and Vincentown formations.   

 

Al Dente highlighted a similar situation in NC where "unusual" folded specimens of P. wilmingtonensis are just included in the same species.  

[Al Dente]

I did some reading a few years ago about modern brachiopods having a lot of intraspecific variation in certain species. There can also be overlap in morphology in some similar looking species. Would probably have to look at internal structure to tell some apart.

[non-remanié]

4 hours ago, Al Dente said:

I did some reading a few years ago about modern brachiopods having a lot of intraspecific variation in certain species. There can also be overlap in morphology in some similar looking species. Would probably have to look at internal structure to tell some apart.

Not surprisingly, it sounds like its complicated.  Do you think that the fact that the "fragilis" are only found in a somewhat isolated community gives more credence to it being a valid species?

 

 From my faint recollections, it seems the smooth and folded P. wilmingtonensis are found together, but that might just be the result of the quarry disturbed sediments from which they are commonly collected.  Perhaps that is not really the case if they are collected in situ from something like a solid streambank exposure.  Do you have information regarding that possibility?

 

 

[Al Dente]

10 hours ago, non-remanié said:

 

 

 From my faint recollections, it seems the smooth and folded P. wilmingtonensis are found together, but that might just be the result of the quarry disturbed sediments from which they are commonly collected.  Perhaps that is not really the case if they are collected in situ from something like a solid streambank exposure.  Do you have information regarding that possibility?

 

 

I’m fairly confident that the smooth and folded Plicatoria are coming from the same layer. Many of the folded ones start out smooth and then suddenly develop the folds. I don’t think I’ve ever found a Plicatoria at a natural outcrop, only in the large quarries. They tend to be found in groups, if you can find one you should look around and be able to find many.