Early Ammonoids

Architeuthoceras

Architeuthis
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#4
Beautiful fossils Hajar, can you see the lobes on the "Erbenoceras", it sure looks like a nautiloid. :heee:

(I guess its just about as close as an ammonoid can get to a nautiloid :sly:)
 

Hajar

Haliphron Atlanticus
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#5
Thanks Kevin. Yes, this one has the ventral lobe, very much like the Bactrites. Otherwise the suture is very simple. I'll take another photo tomorrow.
 

Hajar

Haliphron Atlanticus
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#8
Dr. Christian Klug identifies the specimen above as Gyroceratites and the Anetoceras is now renamed to Ivoites hunsrueckianum or perhaps Bovites. Thanks!

The phylogram below is from DE BAETS, K., KLUG, C. & KORN, D. (2009): Anetoceratinae (Ammonoidea, Early Devonian) from
the Eifel and Harz Mountains (Germany), with a revision of their genera. – N. Jb. Geol. Paläont. Abh., 252: 361–376.
 

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Hajar

Haliphron Atlanticus
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#9
Here's a fine image to illustrate the "Devonian Nekton Revolution" in which the early ammonoids play a major role. It's from a new paper by Klug et al. (2009) and has the caption "Macroecological steps in the evolution of Palaeozoic marine food webs".

Klug, C., Kroger, B., Kiessling, W., Mullins, G.L., Servais, T., Fryda, J., Korn, D. & Turner, S. 2009: The Devonian nekton revolution. Lethaia, 10.
 

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Architeuthoceras

Architeuthis
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#10
Thanks for posting that illustration Hajar, it's great. Do they consider the early nautiloids as macro-plankton until they developed tightly coiled shells, then they became nectonic? Any idea which one of the authors is the artist?
 

Hajar

Haliphron Atlanticus
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#11
Hi Kevin,

This is what they say about early nautiloids:
“Among the nautiloids, all nautiloids originating during the Cambrian, the Actinocerida, Ascocerida, Discosorida, Ellesmerocerida, Endocerida, Lituitida and Oncocerida are here considered demersal; this inference is based on the facies they occur in and morphological features such as coiling and position of hyponomic sinuses (Chen & Teichert 1983; Stridsberg 1985; Westermann 1999; Kroger & Mutvei 2005).”

On orthocerids: “Most orthocerids were probably capable of minor horizontal movements but they were ineffective swimmers and migrated predominantly vertically and/or drifted passively (Hewitt & Watkins 1980; Westermann 1999; Mutvei 2002; Kroger 2003, 2005; Kroger & Mutvei 2005; Mutvei et al. 2007). This is suggested by their poorly differentiated muscle-attachment structures, the absence of significant endosiphonal or endocameral deposits and, in some cases, also shell morphology.”

“The coiled Tarphycerida and Nautilida are interpreted as nektobenthic or nektoplanktonic based on actualistic comparision of the shell form, muscle attachment structures and position of the hyponome (Westermann 1999; Kroger & Mutvei 2005).”

Here below is how they assigned the different animal groups to "ecological megaguilds".

Don't know who the artist is, but I've asked.
 

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Hajar

Haliphron Atlanticus
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#17
Why thank you Terri! I've been travelling and spending a lot of time in the sea and even set up a marine aquarium, but decided not to keep cephalopods in there. It will soon be cool enough to go out into the field here and I'll be back looking at the rocks.
 

Terri

Sepia elegans
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#18
Your welcome, we have had 100+ heat indexes for most of this summer with a lot of rain, which has caused the undergrowth to go wild. Even if I could handle the heat I would have to use a machete to even find an outcrop. But on the bright side the weather is starting to cool off here also!
 

Hajar

Haliphron Atlanticus
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#19
Here's a pile of Devonian ammonoids from Morocco thrown together on my desk. There's Erbenoceras (13 cm at back), Platyclymenia, Gonioclymenia, Cosmoclymenia, Gyroceratites, Agoniatites, Sellanarcestes, Protornoceras, and Acrimenoceras.
 

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DWhatley

Cthulhu
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#20
It would be very interesting to see what that "rams horn" looking (Erbenoceras) animal would have looked like!
 

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