Nautiloid? Help Id please

[Robert Mahorney]

Yes I'd love to get an expert opinion. It's about 620 foot above sea level just at the edge of the nashville dome before the strata begins to deepen and the newer limestone ridge begins to rise. Above the level these were found are multicolored chert layers were crinoids horn coral and button corals can be found in large quantities. Hope this helps identify the formation

[PaleoOrdo]

In the same formation, late ordovician, I found this small nautiloid, a endocerid or orthocerid? The length is 1,5 cm. Maybe an endocerid, since they are know to have been near or at the coast (the location is near the Caledonian mountains in Norway), although they normally lived in the deeper waters? 

 

 

 

[PaleoOrdo]

This nautiloid, which I found in the same formation, if it is nautiloid, does not have visible suture lines. Maybe an oncocerid (?) --for example the genus Beloitoceras, which have been found before in Norway in late Katian time -- because the  shells of oncocerids are bulby in shape and mostly somewhat compressed cyrtoconic brevicones, 'cyrtoconic' meaning a curved, tapering conic form and 'breviconic' meaning short conic, although this short speciemen is relativ straight. Also because the siphuncle in the Oncocerida is commonly located at or near the ventral margin. The siphuncle of the speciemen is relative big and visible near the (ventral?) margin. But it could also be an discosorid, since their shells are also bulby. 

[PaleoOrdo]

The reason for the difficulty to determine if the last nautiloid above is a oncoceroid or a discosorid (or an actionocerid, a similar order which sometimes can be mistaken for the two other orders) is that there is much external shell resemblance between many oncoceroid and discosorid genera. This can be difficult to determine in general without knowledge of the inside of the shells. Moreover, both orders are know to have a large siphuncle relative near the ventral margin or side of the shell. Among the breviconic genera, both of the Discosorida and of the Oncoceratida, the thickening of the shell near the aperture may be quite pronounced. This is different than the actinocerids (at least normally, if I am right?), this order have usually straight shells and appeared earlier, in Floian, Early Ordovicium.

    Some attributes, however, can somtimes be a help for identification of at least the right order: Both oncoceroids and discoceroids appeared first time in the Middle Ordovician, but oncoceroids in Early Middle Ordovician (from 472 my, maybe earlier), discosorids first later in Llandeilian. 

   Are there any externally visible differences of the shell between the two orders to help us ID? That is a difficult question, since there are so many genera of oncocerids, more than of any other nautiloid order. But I attempt indicate a few differences (some expert may correct me on some points):

1. While the siphuncle of oncoceroids are large, the siphuncle of discosoroids are very large, relative to the size of the whole conch (as is seen in the small beautiful specimen I posted above with "bullettes" and wide "circles"/oval form of the connecting rings).

2. Oncoceroids have bullettes with two layers and broader connecting rings. In discosoroids of earlier, Ordovician forms, the bullette became quite large and readily noticeable. In later forms, the bullette became smaller. Discosoroids differ from the Endogastrically curved representatives of the oncoceroids in having a compressed shell. The Discosorida are described as brevicones which are ‘‘endogastric; rarely exogastric’’. Most oncoceroids are opposite curved: exogastric (the longest curve/line is the side which is near the siphuncle). But some is slightly curved.

3. Most taxa of oncoceroids are breviconic, i.e. having a short, straight or slightly curved conch that is rapidly expanding. If I am right, the rapid expansion is not so common among discosorids, although they also are often short or breviconic. Some genera of oncoceroids are not rapidly expanding, some is longer or more curved. Some like Oocerina are gently curved, almost straight, but I am not sure if some genera of oncoceroids have a perfect symmetrical oval shape, but some discosoroids have, as in this speciemen:

 

  

This one I think is impossible to say if it is an oncoceroid or a discosoriod:

[PaleoOrdo]

Two of my speciemen have clearly visible bullettes. The bullettes are pointing in the direction of the apex (the thinner part of the conch). The size of the bullettes are also not the same in each of the speciemen; in one case deceasing in size, in the other maybe increasing in the direction of apex. These attributes, I believe is helpful for better ID of them. But I'm not sure how yet. Anyone have an opinion? Bullettes, in itself or simply, are distinctive or special for the orders of oncoceroids and discosoroids. But it is more to it.

To add, another third speciemen above has also bullettes and is compressed, probable an discosoroid? The bullettes points away from the top; hence, we are looking at the aperture or body chamber on top and a tapering shell. This one (I made the photo more clear):

Edited May 14, 2021 by PaleoOrdo
forgot one relevant photo

[PaleoOrdo]

The last two nautiloids I found in this late Katian formation are one relative large and one very small. The first shown below is the largest nautiloid I have ever found, about 20 cm long. I think it may be an endoceroid? An indication of that order is that the pictures show rounded forms on top of each chamber, that is what is "endocones" if I am right? Moreover, in view of some vertical straight lines, see picture 2 with arrows, (the same as the so-called 'connecting rings'?), the siphuncle is on in the right side position. It seems also much deposits, the black crystals, in the left side of the chambers and near apex. The latter maybe will not help too much for specific ID, because according to I. S. Barskov (et.al): Cephalopods in the marine ecosystems of the Paleozoc, "almost all cephalopods with a straight shell have cameral or/and endosiphuncular deposits allowing orientation and stabilization of the shell in the horizontal position". But I hope someone with more knowledge than me could indicate if it is an endocerid, and maybe the family.

 

The next photo is taken by a microscope, the speciemen seems be 1-2cm long, with an intrusion in the middle part. I'm not sure if it is a nautiloid, but it seems so. Orthoconic? But it have some curve.

Edited May 15, 2021 by PaleoOrdo

[PaleoOrdo]

I have now presented all the nautiloids which I found in this late Katian-Ordovician formation, and it is time to put some quetions and sum up some points (a few photos of them I have posted in another thread). 

1 First, I have found an actinocerid, but it remains unclear to me if I really found a Kochoceras, because some websites writes that these nautiloids were "big". Can there have also been small adult speciemens of this genus?

2. I have also found several Discoceras or different similar species, in all 5 spiral nautiloids.

3. I have found several oncocerids and discosorids, all of them relative small. One of the discosorids is especially interesting, as it is similar to other know species but not the same. Here the small size relative to known bigger similar Middle Ordovician species is obvious. I mean this one, similar to Strandoceras strandi:

4. Among the speciemen I found one middle sized endocerid and a few very small orthocerids.

It is, first, interesting to note with R. C. Frey that Kochoceras was the “flatfish” among nautiloids, "living as benthos, likely crawling on the bottom. A lack of encrusting epibiota on the dorsal surfaces of preserved shells of species belonging to these genera fuels some speculation that these forms may have been ambush predators, living partially buried right under the substrate surface".

Second, the spiral nautiloids are not so small, so it seems they endured climate changes better than other orders.

Third, when I read the article Size Does M a tte r - The Giant Nautiloids of the Arctic Ordovician Fauna by Robert C. Frey, I came to realize that indeed "size does matter". In general it was a development of bigger and bigger nautiloids (and other animals) during the Ordovician, but not always. Frey points out that the so-called “Arctic Ordovician Fauna” is characteristic of widespread "tropical carbonate platform facies of Late Ordovician age" across much of cratonic Laurentia, from what is now northern Greenland to southern New Mexico and that the finds there are similar to the Scandinavian late Ordovician fauna finds, "as the Baltic plate was closing in on Laurentia from the east at this time". The Arctic Ordovician Carbonate Facies had giant nautiloids and are associated with very widespread shallow marine carbonate platform facies. The older, early Late Ordovician fauna was dominated by "often gigantic (meter+ in length) longiconic endocerids, actinocerids, and dissidocerids; massive vase-shaped breviconic oncocerids and discosorids (up to 200 mm in diameter) ...", while "nautiloids and other invertebrates in younger Richmondian 'Stony Mountain' facies typically are smaller in size". I think this is exactly what my finds in Norway also shows, and the reason is the change of the environment in the second period in Late Ordovicium (after 450-448? my) with colder waters and lower sea level.

Edited May 16, 2021 by PaleoOrdo

[PaleoOrdo]

I would like to add to the above that I found 4 species of nautiloids with bullettes, hence, 4 oncoserids/discosorids. Usually and always early in their development discosorids had endogastic shells, but as early as the Late Ordovician the order contained some species with an exogastrically curved and almost straight shell. This make the ID more difficult, since oncocerids usually had exogastric shells. I learned also, according to my source, that nautiloids with exogastric shells was more efficient swimmers than those with endogastric. That explains the "evolution" of these two orders during the Ordovicium, before these were hard hit by the mass extinction. They discosorids (and the oncocerids too with highest genera diversity for a time being) recovered in Silur and developed well in late Devon, then to occupy not only the area just above the sea bottom and was 80% of all nautiloids in existence. The discosorid endogastric genera, and hence this order in it beginning, were benthopelagic, that is, life forms that lived and predated only quite near or on the sea floor, feeding on benthic as well as free swimming organisms.

Source: (PDF) Cephalopods in the marine ecosystems of the Paleozoic (researchgate.net)

Here is a focused photo of the exogastric nautiloid I found ("exogastric" means siphuncle near and the rings on the longer/dorsal side of the shell). By the above reason, it is impossible to see of it is an oncoserid or a discosorid by the curved shape only. It may even be another order since no bullettes are visible? Anyone have an opinion? @FossilDAWG

Edited May 16, 2021 by PaleoOrdo

[Dimitar]

Very interesting topic . Some of the pictures here show signs of melting - lava.

 

 

 

I think these are similar to the nautiloids that I find in Montreal.

 

 

[Ludwigia]

28 minutes ago, Dimitar said:

Some of the pictures here show signs of melting - lava.

 

I'm not seeing any. Can you please explain yourself in more detail.

[Dimitar]

3 hours ago, Ludwigia said:

 

I'm not seeing any. Can you please explain yourself in more detail.

 

On 5/16/2021 at 3:13 AM, PaleoOrdo said:

This picture is one such example:  it`s been melted by high temperature, and the only way to get such high temperature, melting rocks if from lava.

On the site where such specimens were found should be more proofs for such melting, I gess other rocks around would be also melted more or less.  It could be caused by sills and dikes.

[Kane]

No, not melting at all. This is erosion. 

[Dimitar]

On 5/16/2021 at 5:46 AM, PaleoOrdo said:

This specimen was also melted by the lava, we can see on the left side it`s completely melted, on the right side the temperature dropped and it culdn`t melt it. in the middle we see where some sections were partially melted.

[Kane]

Just now, Dimitar said:

This specimen was also melted by the lava, we can see on the left side it`s completely melted, on the right side the temperature dropped and it culdn`t melt it. in the middle we see where some sections were partially melted.

No, not lava at all. This is evidence of erosion. 

[Dimitar]

6 minutes ago, Kane said:

No, not lava at all. This is evidence of erosion. 

The erosion will make the texture more fragile,  will remove some parts of the fossil.  Melting - on opposite - will make it harder, like a ceramic, glass .  Depending on the minerals inside the fossil. You can not erode much on such melted parts, they resist on erosion, these are the best preserved. The owner of the specimen can easily test the hardness of such melted parts and to compare it with non-melted parts.

[Kane]

2 minutes ago, Dimitar said:

The erosion will make the texture more fragile,  will remove some parts of the fossil.  Melting - on opposite - will make it harder, like a ceramic, glass .  Depending on the minerals inside the fossil. You can not erode much on such melted parts, they resist on erosion, these are the best preserved. The owner of the specimen can easily test the hardness of such melted parts and to compare it with non-melted parts.

Please provide documented evidence of volcanic activity in the formation this was found.

 

I find plenty of fossils with this eroded appearance. They are not melted in any way. I think your lava hypothesis is incorrect. 

[Fossildude19]

27 minutes ago, Dimitar said:

The erosion will make the texture more fragile,  will remove some parts of the fossil.  Melting - on opposite - will make it harder, like a ceramic, glass .  Depending on the minerals inside the fossil. You can not erode much on such melted parts, they resist on erosion, these are the best preserved. The owner of the specimen can easily test the hardness of such melted parts and to compare it with non-melted parts.

 

This is incorrect. The fossils are already hardened. The weaker parts are gone, because of erosion - water/wave action, rain, hot and cold, sand and water working together. 

This is all quite common. Your lava theory has no basis in science. If lava was involved, these would be covered in basalt. That is not the case.   

 

[Ludwigia]

I agree wholeheartedly with Kane and Tim. This is why I asked you to explain your thoughts, which as the others have already pointed out, are incorrect.

[PaleoOrdo]

3 hours ago, Fossildude19 said:

The fossils are already hardened. The weaker parts are gone, because of erosion - water/wave action, rain, hot and cold, sand and water working together.

I agree, add to this that the fossils are found on the surface in a field, above the bigger rock beds, already isolated small stones. I think the frequent movement of glaciers in the last ice age in North Europe also contributed to the mentioned erosion. 

[DPS Ammonite]

9 hours ago, Dimitar said:

Very interesting topic . Some of the pictures here show signs of melting - lava.

 

 

 

I think these are similar to the nautiloids that I find in Montreal.

 

 

Limestone does not melt when heated by magma. It decomposes into lime (calcium oxide) and carbon dioxide. Any fossils would be destroyed before the lime was formed. Lime which melts at 4,662°F (2,572°C) will not melt in lava which does not exceed  2,190 °F (1,200°C) 

 

https://www.bbc.co.uk/bitesize/guides/z6gqmsg/revision/2

 

https://en.m.wikipedia.org/wiki/Lava

[PaleoOrdo]

I went this weekend to the same formation and found these two speciemen in the same stone: They seems to be orthoconic nautiloids, ortocerids and show a big living chamber?

 

[PaleoOrdo]

Another rock with two nautiloids. The length of the fatter one is 3cm, the thinner 3,5cm.

The thinner speciemen is oval in cross section, not compressed or have high chambers, has a big siphuncle and it is placed near the margin, seen by the connecting rings on the surface. The siphuncle becomes broader in the mature part of the shell. I cannot see any bulettes, but are there lunettes (which oncocerids have)? Could it be an oncocerid nautiloid? It is known that the siphuncle in the Oncocerida is commonly located at or near the ventral margin, and there are some elongate othoconic oncocerids. According to Flower their connecting rings are thin and siphuncle segments variably expanded as seen here in my speciemen (but also actinocerids have expanded siphuncle segments):

 

[PaleoOrdo]

The fatter speciemen is straight to slightly oval in shape of the shell, round in cross-section, with densly packed chambers. Also in this case the siphuncle is placed at or close to the (ventral?) margin, but it is maybe not so big (a visible connecting ring at the top with a different shape, and two rings in the middle, left side). I do nt know which order this belong to:

 

 

 

[Tetradium]

On 4/14/2021 at 12:46 PM, FossilDAWG said:

The last couple of photos show an actinocerid nautilod.  The "circles" are segments of the siphuncle, which are very inflated and filled with deposits (except for a narrow central canal) in actinocerids.  There are quite a few genera in this group, including Actinoceras, Kochoceras, Armenoceras, and on and on.  A more precise ID would require some investigation of the relevant literature to see what has been described from the local formations.

 

Don

Hmmmm look like you are right. In one Actinoceras species, the siphuncle can be detached from the rest of the shell (it can actually be mistaken  like a smaller cephalopod fossil in its own rights)  so this one is in between. Another new thing for me to learn. 

[PaleoOrdo]

Could the last speciemen be an Gomphoceras? As far as I know they lived from 449 M Y and later. After looking through many articles I cannot find any other order or family which look more similar in shape. It is oval in overall shape, suture lines nicely bended, quite symmetric.