Heteromorphs

[DWhatley]

The presence of a living chamber means this thing died when it was this small.

??? as opposed to it died when it was bigger ????

 

[Architeuthoceras]

As opposed to being the inner whorls of an adult.

An adult would have been about 70-100 mm dia., it would have kept growing septa where the body chamber is on this one. If this was the inner whorls of an adult it would be completely septate. It is just additional data to show we have very young ammonites mixed in with some adults (though not of this genera).

 

[Hajar]

Excellent find Kevin. Do you ever see in-place aptychi in this deposit? I have juveniles with aptychus in place from the Lebanese Cretaceous, but they have diameters ten times larger than your little baby.

 

[Architeuthoceras]

I haven't seen any beaks, they are either not there or maybe I'm just not looking in the right spot. There are casts (or molds?) of fish scales, so if there were beaks floating around in the water they should show up eventually. I will keep looking.

 

[Hajar]

Good luck! Here's an 18 mm youngster and a 40 mm example with aptychus and francolite-preserved soft parts.

 

[Hajar]

The protoconch on this one is about 1 mm across.

 

[Architeuthoceras]

Two from Utah, the top is A. hazzardi from the Coniacian and the bottom one is in my friend Jim's collection, A. annulatum from the Cenomanian. The small one, in the previous post, is Turonian, from the time in between.

 

[Hajar]

Thanks for these - great to see them preserved in 3D.

 

[Hajar]

Here's something not seen very often, a 4 cm Triassic heteromorph ammonite, Choristoceras, from Austria.

 

[Architeuthoceras]

Nice Heteromorph.

Here is a Homeomorph of your Heteromorph.

They both have the same sculpture, it would be hard to separate them if not for some associated fauna.

 

[Hajar]

Which one Kevin?

 

[Architeuthoceras]

Phlycticrioceras trinodosus, The both have the same two rows of ventrolateral nodes and the single row of ventral nodes, and the ribs look very close to each other. Mine is the partial fossil in the lower right hand corner, never have been able to find a complete specimen yet.

 

[Hajar]

I see what you mean. I guess they're not very closely related though. I have an old book putting Choristoceras in Order Ceratitida. For distribution it says "Alps to Timor, N. America and Arctic." Do you ever come across these?

 

[Architeuthoceras]

Choristoceras is a Late Triassic ammonoid, from about 200 Ma. Phlycticrioceras is from the Late Cretaceous, about 85 Ma. About 115 million years separate the two, almost twice the amount of time ammonoids and dinosaurs have been extinct. They are not closely related as taxa nor in time, just a very good example of homeomorphs

I think they find them over in Nevada, but I haven't found any.

 

[POD-L]

heteromorphs

Here is a heteromorph for the new year


Glyptoxoceras subcompressum
Pender Formation
Campanian , Nanaimo Group