What are these bullet-forms?

[PaleoOrdo]

Last summer I visited Helgøya, a place north in the Oslo-field, and found this rock at a site I believe is middle or late ordovician. No other well preserved fossils was possible to find at the site. It is very fragile, so didn't break up the whole rock, but some parts fell of which have clear patterns. It seems the whole rock have some kind of bullet forms inside. Anyone have an idea which kind of animal it is?

Pic.1

Pic. 1

Pict. 2:

Pic.3

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Pic. 6:

Pic. 7:

 

 

Edited August 1, 2021 by PaleoOrdo

[PaleoOrdo]

Here is an up-close of one bullet.

[Al Dente]

Looks similar to Cyclocrinites, a type of algae.

Edited August 1, 2021 by Al Dente

[TqB]

I agree they're calcareous algae. Coelosphaeridium is another one from the Ordovician.

[Tidgy's Dad]

Agree that it's one of the calcareous algae. 

That's a really splendid piece. 

[PaleoOrdo]

Thanks a lot for the informative replies! I'm very happy to have found my first alge. I agree with the options Coelosphaeridium and Cyclocrinites. The pattern is hexagon, 6 sides inside the bullets. The Norwegian lexicon writes that these green alges were indeed present in this island, Mjøsa-area and that this alge means it was places in very shallow waters. It is found there Coelosphaeridium cyclocrinophilum and Cyclocrinus Schmidtii, the first one were more common. Maybe it is that one. The latter one seems to have more densly packed and smaller hexagons among the pictures I found online.

[PaleoOrdo]

According to Johnson (196Ia), Cyclocrinites is distinguished from Coelosphaeridium in having a larger "drumstick-shaped" central stem and large and more slender primary branches with wider bowlshaped tips. He further mentions that Cyclocrinites is more weakly calcified. The age should be Caradoc 455-458 my.

[Harry Pristis]

 

Here's what FOSSILS OF OHIO (1996) says:
Order Dasycladales (calcareous green algae)[dasyclads] 
   Family Dasycladaceae (extinct and recent)
   Family Receptaculitaceae (extinct)   
      Tribe Receptaculiteae [receptaculitids]
      Tribe Cyclocriniteae [cyclocrinitids]
         Genus Cyclocrinites

 

"Fossils of this order [dasyclads] are only rarely recognized by collectors.". . .
 
"Fossil dasyclads are globose to cylindrical or club shaped in outline. They grew on the sea floor to several centimenters in height. 

 

"Internally, a central, noncalcareous structure, the stem or stipe, was surrounded by worled branches or protuberances (rays). . . . They are generally visible only in cracked or broken specimens.

 

"The primary branches or rays of some dasyclads are rounded at the tip; some have bristlelike or spinelike appendages; others have cuplike or prismlike tips that may be fused as an outer covering of small polygons.

 

"In cyclocrinitids, the end of each branch is expanded or branched to form a terminal rhomboidal plate. Each plate is one facet in a fused network of terminal plates of other lateral branches so that the surface of the whole body appears as a reticulate shell of calcareous prisms. . . .

 

"Cyclocrinities is generally a somewhat flattened sphere that has an indentation there the stem (pedicel) was attached. The main central axis was short; lateral branches were very slender, almost rodlike, and arranged in whorls around the central axis. The distal ends of the branches were swollen, and adjacent swollen branch tips coalesced to form the heads, which were polygonal (generally six-sided) in outline at the surface of the spherical body. These polygonal facets were calcified." . . .

The cyclocrinitids range from Middle Ordovician to Middle Silurian in various limestones and dolomites of the Indiana-Ohio-Kentucky Platform.  Cyclocrintes appears widely in these rocks.  Illustrated is a specimen from Late Ordovician, Cincinnatian Stage, Richmondian Series, near Madison, Indiana.

 

 

[PaleoOrdo]

Thanks for the information Harry. If I understand you correctly, the Family Receptaculitaceae and Tribe Receptaculiteae [receptaculitids] are not relevant here (in fact they are now believed to be unrelated and the Receptaculies are not placed in any order yet, see the Beadle & Johnson source below), and then the division of the order D. is:

Order Dasycladales (calcareous green algae)[dasyclads] 
   Family Dasycladaceae (extinct and recent)
      Tribe Cyclocriniteae [cyclocrinitids]
         Genus Cyclocrinites

Moreover, the genus Coelosphaeridium (461-450 my, according to mindat.org, but 460.9 to 455.8 according to fossilworks.org) also is a genus of the tribe Cyclocriniteae. Hence, the ID of my speciemen is surely a cyclocrinitids (461-427 my). A third genus of this tribe is Apidium (458-433 my). The second genus, Cyclocrinites has recorded age 461-439. But Nitecki writes that the oldest cyclocrinitids (the Family) have been reported from the lower part of the Middle Ordovician of California (Nitecki 1970), although they were most abundant during the Caradoc and declined with the cooling of glaciation towards the Ordovician-Sirurian boundary for the family, but total extinction for the genus Coelosphaeridium as early as 455 or 450 my; what could be the reason for the latter, since the cooling not happened yet? It is even more strange since it is known by fossil records in Norway that this genus was much more abundant that the others in Caradoc age.

In an article about the alges in Norway in Ordovicium-Silur (in Norwegian but with a short Eng. summary), JOHAN KIÆR, writes about the finds the Helgøya-Mjøsa district "The Cyclocrinus zones in this district should be compared with the upper portion of the middle Ordovician ... The flora consists of Coelosphæridium, Cyclocrinus and Mastopora." (I think the third genus now in placed within the second).

NGT_06_1_2_113-142.pdf (geologi.no)

By the Early Llandovery in Silurian only two species survived (except Apidium?): Cyclocrinites favus and C. gregarius, and they even may be synonymous. Source: Steven Beadle and Markes Johnson   untitled (palass.org)

 

Edited August 2, 2021 by PaleoOrdo

[Mark Kmiecik]

Beautiful specimens. Worthy of any collection. Nice catch!

[PaleoOrdo]

Thank you, Mark!