Orthoceras regulare cf.

[anonaddict]

location: aarhus, denmark
found: loose beach rock
units: metric
date: 02/10/2024
images:

 

(1) numbered fragments by decreasing size

 

 

 

(2) thick end of the orthocone visible on the surface of the rock in (F1) Ø: 3.5cm

 

 

 

(3) visible centered siphuncle and camerae in (F2)

 

 

 

(4) alternate angle of (F2)

 

 

 

(5) siphuncle and shell exposed in (F1)

 

 

 

(6) fragments (F1) and (F2) held together

 

 

 

 

(7) additional fossils in (F1) likely useless, included for posterity

 

 

 

 

(8) additional fossils in (F3), likely useless. included for posterity

 

 

 

 

(9) small end of orthocone, Ø: 1.5cm, likely useless, included for posterity

 

 

 

 

 

Notes:

 

Found under >200kg rock and ended up breaking it trying to get it loose before even realizing it was a fossil, one of my favorite _Orthoceras s.l._ specimens I've found and includes outer shell

 

Based on the visible camerae and siphuncle _Nautiloidea sp._ (Agassiz, 1847 according to wikipedia)  is the most accurate taxonomic designation I can give, however according to a book on danish beach fossils 'Fossiler - Langs stranden' by Jesper Milàn the most common orthoconic nautiloids found on danish beaches are _Orthoceras_ and _Endoceras_ (s.s. is not specified for _Orthoceras_ but matches with Orthoceras being described earlier as an overall name for orthocone nautiloids but still distinguishing between _Orthoceras_ and _Endoceras_)  with it being _Orthoceras_ if the siphuncle is centered. This also matches with the wikipedia article on _O. regulare_  https://en.m.wikipedia.org/wiki/Orthoceras

 

stating

"Since this work was carried out and re cataloging of the genus, Orthoceras sensu stricto refers to Orthoceras regulare, of Ordovician-aged Baltic Sea limestones of Sweden and neighboring areas."

 

I'm only confident in IDing the red variant of Baltic Sea limestone (or Ølandkalk as it's known in Denmark, it appears to be Folkeslunda Limestone on wikipedia, and some people call it orthoceratite limestone based on the number of _Orthoceras s.l._ ) however I think this lines up considering both the color and contents of the limestone. As such the rock should be from the öland formation but I have no way of confirming it due to it being found as a loose beach rock presumably carried down by glaciers during an ice age

 

As such I arrive at my own best bet of _O. regulare cf._

 

Feedback is very welcome, its my first time doing taxonomic id and i was forced to rely on Wikipedia due to paywall and general lack of information elsewhere despite really not trusting Wiki.

Edited Thursday at 10:32 AM by anonaddict