Mysterious fossils from Campanian St. Bartholomä-formation, Styria, Austria

[FranzBernhard]

I have polished a few slabs today and stumbled over a group of mysterious, tiny fossils. They are in a rudist-bearing limestone clast, width of specimen is 85 mm, they are located a little bit from the center of the specimen toward the lower left corner. Age is Campanian. In the slab 3 mm away from this one, there is nothing to see of them.

I am counting 5 large ones and possibly 3-4 small ones, arranged in 2 or 3 rows. They consist of a thick-walled bubble with a very conspicious plug projecting towards the center of the bubble. One of them has a very conspicous stem and maybe one of the small bubbles has also a stem. The largest bubble has an outer diameter of about 3 mm. Bubbles and the steem appear to be segmented, each segment seems to consist of a single calcite crystal, somewhat resembling echnoid sceletal material. The more often I look at them, the more I think they are tiny crinoids??... But I am probably totally wrong. I tried to make a higher resolution scan and a photo with my scrapy camera at highest resoulution, but without great success. Sorry, better photos are not available.

Suggestions - despite the poor photos - are highly appreciated.

Thanks!
Franz Bernhard

 

[abyssunder]

Very interesting, Franz!
I'm wondering if they can't be juvenile rudists in an early stage of development.

[Bullsnake]

Fascinating!

Too bad they don't show up in any other slabs. It might be interesting to see if a cross-section of one would reveal anything.

[FranzBernhard]

6 hours ago, abyssunder said:

I'm wondering if they can't be juvenile rudists in an early stage of development.

Thats a good idea and certainly a possibility! A very early stage of a rudist pseudocolony. There are two intergrown H. colliciatus in this slab, but 18 mm deeper, there are already four of them intergrown with each other!

5 hours ago, Bullsnake said:

It might be interesting to see if a cross-section of one would reveal anything.

Difficult task and somewhat destructive to the specimen, but not impossible to do. Thanks for the suggestion!

Franz Bernhard

[westcoast]

@abyssunder is correct I believe. Try a search for ontogeny of rudists from San potosi mexico.

[FranzBernhard]

2 hours ago, westcoast said:

Try a search for ontogeny of rudists from San potosi mexico.

Thanks for the info, will do that!
Franz Bernhard

[HansTheLoser]

Stefan Goetz from Heidelberg worked on juvenile rudists; he made serial slabs through rudists limestones from the Upper Cretaceous. I do not know whether he was able to publish something (he passed away in 2012). I would rule out crinoids, but actually I am not a specialist.

[FranzBernhard]

9 hours ago, HansTheLoser said:

Stefan Goetz from Heidelberg worked on juvenile rudists

Thanks, Hans, will try to find something!

Franz Bernhard

[FranzBernhard]

Some interruptions during download of the Potosi papers, but I got at least these:

Rudist larval settlement and ontogony, Stefan Götz, 2003, 1 MB

https://hrcak.srce.hr/index.php?show=clanak&id_clanak=3766

Rudist palaeoecology, Treatise online, Gili & Götz, 2018 (brand new!), 18 MB

https://www.researchgate.net/profile/Eulalia_Gili/publication/323801227_Paleoecology_of_Rudists/links/5aab9c4a0f7e9b840b58c178/Paleoecology-of-Rudists.pdf
Franz Bernhard