"Ammonites are extinct cephalopods that lived in shells. That means their closest relatives are the modern day Nautiluses, Octopi, Squid, and Cuttlefish. Like the Nautilus, Ammonites gradually add onto their shell to accommodate their increasing body mass. As they extend their shell they build a wall, closing up the now too narrow portion of the shell behind them as they move into the larger portion of the spiral.
In the Cleoniceras Ammonite, unlike the Nautilus, the morphology of the tissue wall they build between the chambers is not just a smooth curved wall. Instead it has a bizarrely complex fractal 3-dimensional shape. These patterns are called “suture patterns” and they mark the intersection of the septum walls with the shell. Scientists can’t agree why the septum walls are so complexly furrowed or even how they formed. But they certainly have published many conflicting arguments about the subject.
Possible Scenarios:
1. Hammer proposes a reaction-diffusion explanation for the
formation of suture patterns (right below) 2. Checa and
friends propose a viscous fingering explanation, where the two
fluids at play are the cameral liquid and connective tissue
(left below) 3. V. De Blasio uses finite element analysis to
argue that the high sinuosity is an evolutionary response to
external pressure, reinforcing the shell in response to
hydrostatic pressure"
Possible Sources:
Hammer, Ø. 1999. The development of ammonite septa: an
epithelial invagination process controlled by morphogens?
Historical Biology 13:153-171.
Hammer, Ø. & Bucher, H. 1999. Reaction-diffusion
processes: Application to the morphogenesis of ammonoid
ornamentation. GeoBios 32:841-852.
García-Ruiza, J. & Checa, A. 1993. A model for the
morphogenesis of ammonoid septal sutures. GeoBios
26:157-162.
Lewy, Z. 2002a. The function of the ammonite fluted septal
margins. Journal of Paleontology, 76::63-69
De Blasio, F.V. 2008: The role of suture complexity in
diminishing strain and stress in ammonoid phragmocones.
Lethaia 41:15–24.
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