- Joined
- Nov 19, 2002
- Messages
- 3,031
Just a quick thought before I go to bed (no time to look up anything detailed today). I may be talking completely over-simplified cobblers, but here goes anyway.....
Perhaps each different form of 'heteromorph' nautiloid was particularly specialised and occupied it's own narrow ecological niche. The decline of the nautiloids in their more exotic varieties during the Devonian and Early Carboniferous certainly seems to coincide with the rise of the early ammonoids, i.e the earliest goniatites, bactritids, and some of the other obscure groups. Maybe these new forms 'squeezed' out the nautiloid specialists and occupied some of their niches, forcing the remaining spiral-shaped nautiloids into increasingly deeper waters where they were not in direct competition.
I know a few heteromorph ammonoid forms suddenly appeared in the Triassic, but by time of the heyday of the ammonoid heteromorphs the nautiloids were confined to deeper waters; there was no such competition preventing experimentation amongst the ammonoids as they were not fighting for the same space. In an increasingly hot and tropical environment, this allowed them, specifically the Ancyloceratina, to explore their maximum developmental potential. By then the coleoids were in ascendancy but these appeared to have lived very different lifestyles and were not in direct competition.
I'm sure the real answer lies somewhere in the genomes and mutation potential within DNA, though. (Must ask Richard Dawkins to explain).
As an aside, here is a fantasic depiction of the Ordovician nautiloid Estonioceras for you.
Perhaps each different form of 'heteromorph' nautiloid was particularly specialised and occupied it's own narrow ecological niche. The decline of the nautiloids in their more exotic varieties during the Devonian and Early Carboniferous certainly seems to coincide with the rise of the early ammonoids, i.e the earliest goniatites, bactritids, and some of the other obscure groups. Maybe these new forms 'squeezed' out the nautiloid specialists and occupied some of their niches, forcing the remaining spiral-shaped nautiloids into increasingly deeper waters where they were not in direct competition.
I know a few heteromorph ammonoid forms suddenly appeared in the Triassic, but by time of the heyday of the ammonoid heteromorphs the nautiloids were confined to deeper waters; there was no such competition preventing experimentation amongst the ammonoids as they were not fighting for the same space. In an increasingly hot and tropical environment, this allowed them, specifically the Ancyloceratina, to explore their maximum developmental potential. By then the coleoids were in ascendancy but these appeared to have lived very different lifestyles and were not in direct competition.
I'm sure the real answer lies somewhere in the genomes and mutation potential within DNA, though. (Must ask Richard Dawkins to explain).
As an aside, here is a fantasic depiction of the Ordovician nautiloid Estonioceras for you.