Heteromorph ammonites- why the weird shapes?

[aplomado]

Heteromorph ammonites- why the weird shapes?

 

I am at a loss...

[digit]

Aside from mimicking a trombone, I too have often wondered.

 

Let's see if someone has that answer locked away in their deep knowledge base.

 

 

 

Cheers.

 

-Ken

[facehugger]

Think these are just variations with the ammonite group...kinda like some people have curly hair and other have straight hair. Haven't seen an evolved purpose for the uncoiled shells. Some research indicates that some heteromorphs evolved into coiled shells later on before final mass extinction at end of Cretaceous. 

 

Bound to be some ammonite experts around here with more info, though...

[Wendell Ricketts]

At the risk of tooting my own horn, as they say, I highly recommend the Spring 2019 issue of Fossil News, in which we did a large spread on heteromorphs, including information on probable advantages/disadvantages of those convoluted shells. You can see the table of contents here: https://fossilnews.org/backissues/spring-2019/. Best of luck, W.

[TqB]

 Adaptations to a particular lifestyle, exploiting a niche. Earlier cephalopods did it too, especially nautiloids. Why is anything the shape it is?

[aplomado]

I usually expect swimming critters to "areodynamic" to swim more easily through the water... some heromorphs are not, at all...

[aplomado]

18 minutes ago, TqB said:

 Adaptations to a particular lifestyle, exploiting a niche. Earlier cephalopods did it too, especially nautiloids. Why is anything the shape it is?

 

What niche requires a shell shaped like this?

[digit]

Obvious mimicry so it can sneak up on its preferred diet item.

 

 

 

Cheers.

 

-Ken

[piranha]

Seilacher, A. & Gishlick, A.D. 2015

Morphodynamics. CRC Press, 514 pp.

[aplomado]

So, maybe to enable a sponge symbiote?

Cool!

[FossilDAWG]

53 minutes ago, aplomado said:

So, maybe to enable a sponge symbiote?

Cool!

The sponge symbiote was mentioned only for Nipponites, which was likely sessile on the sea floor.  The others, such as the nostocerids, are thought to have moved up and down in the water column.  Planispiral (normally coiled) ammonites were streamlined for horizontal movement through the water, as (for example) in swimming after mobile prey.

 

Don

[RuMert]

As evolution is not trying to reach any goal but throws in variants that are later tested for "fitness", cretaceous ammonites found themselves in such favorable enviroment even odd species like heteromorphs survived 

[Wendell Ricketts]

3 hours ago, TqB said:

 Adaptations to a particular lifestyle, exploiting a niche. Earlier cephalopods did it too, especially nautiloids. Why is anything the shape it is?

Well, arguably, because there was a selective advantage to being that shape or, at least, no disadvantage to being that shape. So the question is a legitimate one, and the possible answers are interesting.

[caldigger]

The real reason is the same as why people color their hair purple or tattoo their body.  

Cephalopods were just expressing their individuality and trying to be different. Not conforming to the normal coils and straight shells the rest of the Cephalo society was presenting. 

 

"REBEL CEPHS" if you will.

[Randyw]

20 hours ago, aplomado said:

 

What niche requires a shell shaped like this?

Protecting its soft tasty bits from predators?

[FossilNerd]

Could they be genetic abnormalities/mutations that happen to occur when the wrong genes get mixed together?  Maybe the heteromorph got the wrong recessive trait from one or both of its parents and it’s shell grew in an unusual shape. So not necessarily an evolutionary adaptation, but more of a genetic disorder.

 

 

[Randyw]

1 hour ago, FossilNerd said:

Could they be genetic abnormalities/mutations that happen to occur when the wrong genes get mixed together?  Maybe the heteromorph got the wrong recessive trait from one or both of its parents and it’s shell grew in an unusual shape. So not necessarily an evolutionary adaptation, but more of a genetic disorder.

 

 

Oooo I like that thought! Hypothetically what if the coiled and straight versions were close enough genetically to interbreed and what if they reproduce by releasing eggs and sperm into the water. And sometimes a coiled egg is fertilized by a straight sperm resulting in a genetic mutant like a mule. The fact that it would be sterile wouldn’t have an adverse effect because with million of each spawning in the water the mutation would have a chance of reoccurrence 

[digit]

In the "Golden Age" excerpt posted above, the hypothesis is that these heteromorph ammonites did not swim rapidly through the water chasing prey but instead rose up and down through the water column like a Cartesian Diver.

 

https://en.wikipedia.org/wiki/Cartesian_diver

 

I can imagine how the "top knot" of twisted chambers might possibly function as the float allowing these ammonites to adjust their buoyancy and efficiently traverse the water column vertically with very little effort and energy expenditure. It is well known that modern day nautilus make diurnal migrations so this is not particularly far fetched given what we know about their extant kin.

 

https://en.wikipedia.org/wiki/Nautilus#Buoyancy_and_movement

https://asknature.org/strategy/siphuncle-controls-buoyancy/

 

 

An interesting topic to ruminate over--anybody else have any links to physiology papers on heteromorph ammonites?

 

 

Cheers.

 

-Ken

[FossilDAWG]

Peter Ward at the university of Washington has published on the hydrodynamics of heteromorphic ammonites.  I'll see if I can find links to his papers.

 

Don

[digit]

That would be sweet. I usually choose to grow my fossil knowledge in an idiosyncratic way by studying in-depth whatever novel new find I've added to my collection but these heteromorphs seem so bizarre that I may just have to load up on some knowledge before adding any to my collection. BTW: Are there any known places where one might fossil hunt with a reasonable chance of finding heteromorphs?

 

 

Cheers.

 

-Ken

[FossilDAWG]

9 hours ago, Randyw said:

Oooo I like that thought! Hypothetically what if the coiled and straight versions were close enough genetically to interbreed and what if they reproduce by releasing eggs and sperm into the water. And sometimes a coiled egg is fertilized by a straight sperm resulting in a genetic mutant like a mule. The fact that it would be sterile wouldn’t have an adverse effect because with million of each spawning in the water the mutation would have a chance of reoccurrence 

Heteromorphic ammonites are not some rare chance mutant.  In many formations they are the dominant ammonites, and some species are common and distinctive enough to be used as zonal indicies.  For example species of Didymoceras characterize three biostratigraphic zones in the Pierre Shale in the western interior, and Nostoceras species are indicies for late Campanian and lower Maestrichtian strata worldwide.  Further, clear evolutionary lineages are found in many of these successions of species.  Baculites, a straight-shelled ammonite, is also a heteromorph BTW; the initial shell is normally coiled before it straightens out.

 

So no, heteromorphic ammonites are not chance "mules" produced by interbreeding "normal" and "straight" ammonites 

 

Don

[FossilNerd]

16 minutes ago, FossilDAWG said:

Heteromorphic ammonites are not some rare chance mutant.  In many formations they are the dominant ammonites, and some species are common and distinctive enough to be used as zonal indicies.  For example species of Didymoceras characterize three biostratigraphic zones in the Pierre Shale in the western interior, and Nostoceras species are indicies for late Campanian and lower Maestrichtian strata worldwide.  Further, clear evolutionary lineages are found in many of these successions of species.  Baculites, a straight-shelled ammonite, is also a heteromorph BTW; the initial shell is normally coiled before it straightens out.

 

So no, heteromorphic ammonites are not chance "mules" produced by interbreeding "normal" and "straight" ammonites 

 

Don

Thanks for the enlightenment Don! I was trying to think outside the box with the genetic mutation hypothesis; that Randy then expanded upon. 

 

I wasn’t aware that heteromorphs were common enough in certain strata to identify them. I was also unaware that belemnites were heteromorphs. Very cool! 

 

I was thinking along the lines of the genetic mutation that may be spread through recessive genes, like red hair or blue eyes for example, and not necessarily a product of straight shelled ammonites and normal ammonites. However, if there is clear evolutionary lineage, and enough specimens to identify strata, it would eliminate that possibility as the combination of recessive genes needed to produce a red headed, blue eyed ammonite, would be a rare occurrence. 

 

P.S. I know that blue eye color is no longer thought of as being “just” a recessive gene trait and that eye color is a complex thing, but I think the example gets the idea across as most people still tend to think of blue eyes as a recessive trait.  

 

 

[Pagurus]

18 hours ago, caldigger said:

Not conforming to the normal coils

 

They shuffled off this mortal coil. 

[Adam86cucv]

5 hours ago, Pagurus said:

 

They shuffled off this mortal coil. 

Remarkable ammonite, beautiful plumage.

[Randyw]

@FossilDAWG I don’t believe they are either wich is why I said hypothetically. But it’s still fun to sometimes think outside the box like I and @FossilNerd were doing. A little what if has never hurt anything.

Remember feathers on dinosaurs was once a pie in the sky thought. Not that I agree with everything baker proposes but his statement about throwing things out and seeing what sticks as a way of motivating scientific discussion can be both fun and enlightening.