Why are we so sure there are no recent ammonites?

shuemmerich

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Dear Cephalopod Enthusiasts,

first of all, please forgive me if this hasn't been posted in the right forum - it didn't seem to fit in anywhere, so I chose "Physiology and Biology" (Mods, please feel free to move this anywhere you think appropriate!).

I'm a big fan of Danna Staaf's book "Squid Empire", which I have recently read another time. She gives a truly enthralling view of the cephalopod history ... but I'm not writing an advertisement.

While re-reading the book another time, however, a question kept nagging at me: on what grounds are we so sure that ammonites no longer exist today? I confess that I'm an ammonite lover and this is probably just borne of wishful thinking but if anybody could spend some time to shed more light on this, this would be much appreciated, indeed!

For instance, in the "Study of Deep-Sea Cephalopods" by Hoving et al. (Adv.Mar.Biol. 2014; 67:235-359), we read that only "[...] less than 0.0001% of the deep-sea flor have been investigated." I know that shelled cephalopods couldn't go deep but seeing that e.g. baculites seem to have thrived around methane seeps, why is everybody so sure that there won't be some kinds of ammonites left around some methane seep or in any other obscure habitat somewhere in these unexplored vast reaches? Maybe for some reason the shells of these animals don't drift long ranges, we wouldn't know they are there, would we?

I know that the fossil record of ammonites breaks off waaay in the past. However, the fossil record of the coelacanthiformes breaks off 70 mil. years ago, everybody considered them extinct, but we know since the 90s that they are still present in our oceans today.

So, considering that (a) we know next to nothing about the greater part of the oceans and (b) some species have survived to the present day even when their fossil record breaks off, what makes everybody so 100% sure that this might not be the case with ammonites, too? Maybe this is all very obvious and I just don’t get it, but I’m really wondering…

Thank you for taking the time to read all this and best wishes from a lover of the head-footed,

Stefan Hümmerich
 

Mark Carnall

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Until they are found living in the deep ocean we will have to follow the existing evidence and assume they died at the K/T boundary along with the dinosaurs :(

Also a big fan of "Squid Empire"
'Most' of them anyway ;) I found out about Palaeogene ammonites from Netherlands, Denmark and USA from Squid Empire!
 

Danna

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This is such an awesome question! (also I'm so so glad y'all liked the book :blush::heart:)

First let me say that I too have yearned for a coelacanth-style discovery of extant ammonites, so I'm right there with you in that dream. We can't say it's 100% impossible, but it does seem EXTREMELY unlikely for a few reasons.

You're on the nose about ammonites being depth-limited by their shells. The seep-dwelling ammonites wouldn't have been living at super-deep methane seeps (thousands of meters down) but rather at shallow seeps of a few hundred meters depth or less. (Methane seeps in today's oceans can occur at any depth, even intertidally!) At that depth, our oceans are much more thoroughly explored, so it would be REALLY surprising to have missed ammonites.

As you noted, the shells also give us other reasons to be pretty sure that ammonites have gone extinct. We know that ammonite shells fossilize in abundance wherever these animals are present--that's what makes them such good index fossils and so popular with collectors. So the fact that they disappear from the fossil record shortly after the K/T extinction is a big deal, compared to the scant fossil record of coelacanths, which was never very thorough or abundant to begin with.

Plus, all modern cephalopod shells (from nautilus shells to cuttlebones to spirula) drift and wash up on beaches and are pretty easy to find (I've found plenty of spirula shells despite never seeing a live animal) so it would be pretty weird if there were some living ammonite whose shells just never ever get found.

It's inevitable that we will discover new species of cephalopods in the deep sea as we continue to explore, but they're almost guaranteed to be coleoids, not ammonoids or nautiloids. Still exciting!

Hmm. I may need to write a sci-fi short story exploring "what if the ammonites survived???" Idea prompts welcome. ;)
 

shuemmerich

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Dear Danna,

thank you very much for taking the time and sharing your thoughts on this! You raise some very good points and I see now that a coelacanth-style rediscovery of ammonites is extremely unlikely, indeed. Still, "extremely unlikely" sounds better than "impossible". :smile:

Quite possibly, what got me hooked on this topic besides an intrinsic love for shelled cephalopods is the finality with whom at least the sources I've read comment on the matter. It's mostly like "ammonites died out at the K/T boundary, period". I'd be much more comfortable with something like "according to existing evidence, ammonites died out ...". But that's probably just me splitting hairs about wording...

"Hmm. I may need to write a sci-fi short story exploring "what if the ammonites survived???""
I'm very much pro this idea! 👍

Thanks, all of you, for taking the time and best wishes,

Stefan
:bactritin
 

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