Request for help in mollusc research

[jwduke109]

Hey everyone. My name is Josh Weinstein and I'm a senior at Duke University in North Carolina. I am currently working with the evolutionary biologist, Dan McShea, on an independent study relating to body size trends. The idea is that maximum body size in animals is always increasing. So, the largest mollusc now (giant squid) is larger than any other mollusc in evolutionary history, just as the blue whale is the largest chordate ever to live.

Basically, the question I am trying to determine is whether MAXIMUM (not average) body size is a passive trait, meaning increasing max body size is completely random, or a driven trait, meaning max body size increases because it is selected for.

I am working with 2 other students, and I am responsible for finding the answer to this question with molluscs. I must do this by determining the largest molluscs at each given time during evolutionary history, plotting it on a graph, and searching for trend lines. So far, I think I have two data points - the giant squid (contemporary), and Pachydiscus seppenradensis (cretaceous).

My question to everyone on this forum is, can you help me in my research? Can anyone tell me the largest gastropod/cephalopod/etc. from any given time period (Ordovician, Silurian, etc.)? If anyone thinks they can help me, or would just like to find out more about my research, please send me a message or, better yet, shoot me an email. Thanks everyone for your time, and I'll be sure to let everyone know the results of my research. I'm looking forward to hopefully hearing from some of you.

Best,

Joshua H. Weinstein
Duke University
[email protected]
Major: Biology
Minor: Philosophy

 

[mucktopus]

Many factors, especially evolutionary history, play a role in determining body size (indeed- this is an evolutionary question you're asking). Looking at maximum size across all cephs through time is possible, but I'm not sure how much you can really learn from it given the diversity within the group. It would be better to map the sizes onto a phylogeny and run tests from there.

 

[chrono_war01]

With all due repect, Josh. Starting a whole load of the same thread is not going to help you...at least not on this website.

 

[Phil]

Hi Josh,

Nice to have you here and welcome to TONMO. Here's a few stats and names for you on prehistoric giant cephs.

So, the largest mollusc now (giant squid) is larger than any other mollusc in evolutionary history, just as the blue whale is the largest chordate ever to live.

I'm not really sure one can make this assumption. As you say Pachydiscus (actually now called Parapuzosia seppenradensis) is the largest ammonite yet discovered with a shell diameter of 2.2m, but the completeness of the ammonite fossil record is vastly greater than the soft-bodied forms. The fossil record of squid and octopus is absolutely appalling as the things simply don't fossilise except in the most exceptional of circumstances. The fossils we do have tend to come from shallow water esturine - type deposits; who knows what animals lurked out in the ancient oceanic abyssal waters. Remains of such animals would have been buried under deep-water sediments that would never become exposed or may have been destroyed in subduction under continental plates.

Maybe Architeuthis and Mesonychoteuthis are the largest coleoid cephalopods to have evolved, but maybe there were once even larger forms that have left no trace. This is something that we will simply never know unfortunately. It's interesting thought that if a paleontologist took a time machine 100m into the future, he would almost certainly find absolutely no fossilised traces of Architeuthis unless he was extremely fortunate indeed.

Basically, the question I am trying to determine is whether MAXIMUM (not average) body size is a passive trait, meaning increasing max body size is completely random, or a driven trait, meaning max body size increases because it is selected for.

This is a good question and I'm really not sure of the answer. Maybe John (FJ) would have an opinion?

I must do this by determining the largest molluscs at each given time during evolutionary history, plotting it on a graph, and searching for trend lines. So far, I think I have two data points - the giant squid (contemporary), and Pachydiscus seppenradensis (cretaceous).

Best of luck! As Mucktopus has stated I'm not sure what conclusions can be drawn from the giants of each group as they have very disparate morphologies, and are widely separated on the family tree. I'm sure we'd like to read your conclusions though.

My question to everyone on this forum is, can you help me in my research? Can anyone tell me the largest gastropod/cephalopod/etc. from any given time period (Ordovician, Silurian, etc.)?

Well, glad to be of help,

Nautiloids

Cameroceras was a giant endocerid nautiloid and is believed to have grown up to 10m in length, excluding the soft-bodied head. It lived in the middle Ordovician and fossils are known from North America. It was, of course, top predator of the period.

Ammonites

Parapuzosia seppenradensis (a.k.a Pachydiscus seppenradensis)was a Late Cretaceous ammonite from Munster in Germany, It measures a gigantic 2.2m across, and even at this size it lacks the living chamber! The entire fully grown animal may have measured in excess of 2.5m. Probably an unremarkable swimmer, this ammonite proably hunted or scavenged on the seabed. You can see images of it in this old thread.

Belemnites

Megateuthis gigantea is the largest belemnoid yet found. It is middle Jurassic in date and has been found in the Jurassic of Europe and Asia, had a rostrum measuring 50 to 60 centimeters in length, making the overall shell up to 2 meters, which would give the living animal an estimated length of 3 metres or more (depending on the length of the tentacles).

Squid

Aside from the modern giant squids, the Late Cretaceous Tusoteuthis probably rivalled Architeuthis in mantle length. A very rare fossil with only a handful discovered, it is considered to be a vampyromorph and not directly on the decapod lineage that led to modern squid. Hailing from Kansas and Manitoba, the gladius in the few known specimens has been recorded up to 1.8m. I drew together every scrap of information I could last year for an article on this beast and if interested please have a look here.

The family tree of cephalopods might be of some interest too.

All the best!

Phil

 

[DHyslop]

Hi Josh,

Cope's Law is much less a "law" than, perhaps an "observed tendency." As Phil pointed out, some nautiloids became truly massive during the Paleozoic: molluscs that would put architeuthis to shame!

One good reference to check out is John Tyler Bonner's The Evolution of Complexity. I believe the first two chapters relate to Cope's Law specifically. He talks a lot about the kind of specialization required just to become large.

Dan

 

[Fujisawas Sake]

With all due repect, Josh. Starting a whole load of the same thread is not going to help you...at least not on this website.

Eric,

Huh? I'm not sure I understand what you meant there.

Joshua,

to TONMO.

Wow! That's a hell of a project. Sounds like quite an undertaking. I do have a few questions, though:

1) Are you wondering if size-change is an evolutionary trait across the entire Kingdom Animalia? If so, are you splitting this somehow, like Deuterostomes vs. Protostomes, Invertebrates vs. vertebrates, etc.?

2) Are you taking into account geological time periods and how mass extinctions affected representative “dominant” megafauna? 'Dominant' being in quotes because, well, as far as populations are concerned, the Chordata are a minority.

3) Are you also taking into account the percent of the population that are, by the standard of the Phyla, “giants”?

Its easy to say that size is completely affected by selection, but I have a feeling that there are far more factors than any one kind of selection. I think size is a specialization, a result of selection rather than the random, mostly since you need a lot of physiological specializations to obtain and keep a "giant" size across your species. Metabolic and energetic scaling HAS to be taken into account though. Of course, as Steve O'Shea reminded me some time ago, 'giant' is a relative term. That's only my opinion, however, so it's by no means "scientific"; just patterns I've noticed.

Cope wasn't a bad thinker - like most of the Neo Lamarkians he saw patterns in nature and wrote about them. He wanted to look for divine intervention in nature, but I think Cope's may have been on to something - at least in dealing with so-called “dominant” species. Huge sizes do pop up in nature across geological time periods, but these operate within given physiological and ecological constraints (for example - why are no land mammals the size of sauropods, or why did the majority of the Dinosauria seem to be getting smaller near the end of the Cretaceous?).

If you don't mind, I would like to ask you if you could, upon completion of your paper, post it on this site. I would like to see what conclusions you draw.

I would also suggest looking at other molluscs as well. Cephs are great, but their level of morphological specialization sometimes prejudices us against comparative studies across the rest of the Phylum. Molluscs are bloody BRILLIANT when it comes to diversity across the body plans. I just feel that cephs are not always the ideal mollusc for this type of study, since there is so much more fossil evidence where gastropods and bivalves are concerned. (I KNOW I'm going to get flack for saying that ).

Best of luck.

John

 

[Phil]

Josh,

Have a look at this old thread. Many interesting ideas there:

Abyssal Gigantism

Just as a vague thought, gigantism seems to coincide with periods of elevated oxygen (e.g giant arthropods in the Carboniferous). It might be worth trying to research ancient levels at the times of the creatures you are interested in.

Phil

 

[Architeuthoceras]

to TONMO Josh,

I have heard stories of 12 foot Inoceramid bivalves in the Late Cretaceous, never found one myself but I have seen huge piles of broken shell (individual pieces up to almost an inch thick) that suggest gigantic size.

 

[bigGdelta]

Basically, the question I am trying to determine is whether MAXIMUM (not average) body size is a passive trait, meaning increasing max body size is completely random, or a driven trait, meaning max body size increases because it is selected for.



Joshua H. Weinstein
Duke University
[email protected]
Major: Biology
Minor: Philosophy

Possibly body size could be both. Gould once said something to the effect that it is the best adapted LUCKY organism that survives--even the most perfectly darwinian adapted fish will die if its lake dries up. The obvious factors would be food supply and predation but what if a gene for greater body size was tied to some other pro-survival genetic trait and the increased size was just a null factor. In that case body size might increase without evolutionary pressure for a larger organism .

 

[chrono_war01]

Eric,

Huh? I'm not sure I understand what you meant there.

I think a admin or mod has taken care of this, but there used to be 4-6 of these Topics floating around in the different sections...there was one in Tank Talk, one in Introduce Yourself and on and on...anyway..it has been taken care of.

 

[Steve O'Shea]

Way cool, interesting thread, but I do have to ask how you are measuring size, particularly w.r.t. squid/octopus. Is it mantle length (ML), standard length (SL), total length (TL), or in terms of weight? Depending on what measure you use, particularly in cephalopods, you will get quite different size 'maxima'.

Perhaps finer-scale resolution is required, and look at gigantisism in certain families of squid or octopus (Recent at least), and for the extinct taxa, e.g. ammonites, define it as maximum shell diameter (and worry about whether that shell was internalised or externalised at another time (the animal could have been of considerably greater size than the shell, in the event the shell was entirely or even partially internalised)).

Perhaps, with specific reference to Recent taxa, you should also look at latitudinal trends in size, or look at bathymetric shifts in size. Gigantisism is a purely relative term (a 'giant' elephant would be considerably larger than a normal-sized elephant; a normal-sized elephant is considerably larger than either a giant or colossal squid).

Tintenfisch has actually taught something on this quite recently in one of her lectures. Perhaps I should prop her with my giant finger and see if we can elicit a response from her.

 

[Feelers]

The idea is that maximum body size in animals is always increasing. So, the largest mollusc now (giant squid) is larger than any other mollusc in evolutionary history.
Basically, the question I am trying to determine is whether MAXIMUM (not average) body size is a passive trait, meaning increasing max body size is completely random, or a driven trait, meaning max body size increases because it is selected for.

Are you trying to cover everything? It sounds like a MASSIVE topic if you are trying to apply it to every (relatively) large animal.
I believe that with giant beatles for instance, they are limited to a certain size because of their "circulation" system. Air can only diffuse so far and that is supposedly why they can't get any bigger. There is a defined size limit, and unless they have a major system overhaul, which is incredibly unlikely, they are stuck at an evolutionary coldasack, even though they probably "want" to get bigger.

 

[Jean]

There is also something called (I think!) the cube square law which deals with the size animals with exoskeletons can get. Apparently the way the tendons and ligaments attach to exoskeltons limits the size they can grow to.

Always remember seeing a movie years ago about an underwater facility that was terrorised by a HUGE carniverous crustacean (I'm talking 8-10 feet tall) Needless to say all the hapless scientists got munched except for our hero and heroine, but why it stuck in my mind is that the day after it screened our zoo lecturer gave an hour long dissertation on why it wasn't possible and the above is what I remember....the movie was called deep six or deep star six..........something like that anyway!!

J