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NAUTILOID vs. AMMONITE


da_capo

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Hi

 

I am composing a table of comparisons between nautiloids and ammonites (mainly internal and external anatomy but a couple of extras too) and was wondering if anyone had anything they could add to what I have already? (Table attached)

 

Cheers in advance

 

Mark

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Enlarged and brightened:

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So, at the risk of sounding thick... rhyncholites are the mandible correct? So I assume these can be proven to be present in nautiloids, but is there fossil evidence of them in ammonites??

 

This may be ignorant and totally wrong but just correct me if so!

 

Cheers

 

Mark

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17 minutes ago, da_capo said:

So, at the risk of sounding thick... rhyncholites are the mandible correct? So I assume these can be proven to be present in nautiloids, but is there fossil evidence of them in ammonites??

 

This may be ignorant and totally wrong but just correct me if so!

 

Cheers

 

Mark

Rhyncholites are the tip of the upper jaw, I believe, the lower jaw specimens being known as conchorhynchs.  

They are rare finds but seem to have occurred in both ammonoids and nautiloids.from the Upper Palaeozoic to the recent Nautilus. 

https://onlinelibrary.wiley.com/doi/abs/10.1111/j.1502-3931.1980.tb01046.x

Also, ammonites are not found in the Devonian, the order Ammonitida occurs from the very end of the Triassic, ammonoids (subclass Ammonoidea) appeared in the Devonian, bu that's not the same as ammonites. 

 

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As far as I know, rhyncholites are usually associated with nautiloids, but have also been found in some ammonites. Other possible differences:

a) Ammonite males can have (more or less long and weird) lappets and these are usually sought after, but rarely preserved. 

b)Ammonites did not have a  hood while nautilluses do

c) Ammonites had 10 arms with suckers - the arms of nautiluses are numerous suckerless cirri, whose number can reach 90

d) Ammonites lived  mostly in shallow waters while nautiluses - in ocean depths, so much more ammonite shells are found today

e) Some adult ammonites were very big, reaching 2+m in diameter

f) At the same time a newborn nautilus is bigger than the ammonite one and hatches from a bigger egg

g) Ammonites  males and females were oftern described as different genera and the aptychi  as a different animal group, and the names are still in use. For example, Sutneria Zittel 1884 and Aspidoceras Zittel 1868 are males and females of the same genus.

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Slightly off topic...

https://www.luckysci.com/2014/05/the-quick-difference-between-nautiloids-and-ammonoids/

There is a picture at this website that is a great novice intro ... reproduced here:

Hopefully your end product will include pictures and photos... I imagine TFF member @RJB has a photo or 2 of each that would knock your eyes out. :D

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I can’t contribute to this thread, but I wanted to thank all who have. :) 

 

I haven’t studied much on Ammonites/Nautiloids yet and this thread has piqued my interest. I’m learning from here and elsewhere ;). Any day I can learn something new is a good one. Thanks for making my day a little brighter! 

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Great idea. I can see you have put a lot of effort into this. There are a couple of things I can see that might be confusing and both involve over-generalization.

First, when it comes to whorl shapes it is not always the case that all nautioids are depressed or that all ammonoids are compressed. Ammonites in particular come in a large variety of whorl shapes. As a tool for comparison this might be better with that caveat made clear.

The second generalization is with ornamentation. What you have is certainly true for most Mesozoic forms but the opposite is true for many from the Paleozoic. Pennsylvanian cephalopods are the ones I know best and most coiled nautiloids from that sub-period are ornamented while most ammonoids are not.

 

Something you might want to add to the differences,  in addition to lappets, is the occasional presence of features like a rostrum or ventral keel in ammonoids that are not present in nautiloids as far as I know.

 

edit: I just noticed that your chart compares nautiloids to ammonites, not all ammonoids. That fact renders my observation about ornamentation moot since there were no ammonites during all but the very end of the Paleozoic so that generalization is useful in that context.

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