Megalodon size

[creature386]

Aug 3, 2013 23:36:03 GMT 5 theropod said:

Please don't start to bring your beloved theropods on that field. Terrestrial and oceanic predators rely on different variable. And T. rex had preys potentially much heavier than itself.

T. rex is evidently not a "gigantophagous specialist", this is widely agreed upon, reflected by its ecosystem and its morphology.

Remember that he said there are differences between marine and terrestrial predators. As for marine predators, I have found a paper talking about predator/prey size relationships in marine animals: people.uncw.edu/scharff/publications/MEPS%202000.pdf

The range of absolute prey sizes eaten expanded with increasing body size for all predators examined. As body size increased, all predators showed a significant increase in maximum prey size consumed, while 12 of 18 predators increased minimum prey sizes eaten (Fig. 2, Table 2).

[theropod]

Thanks for the paper!
This demonstrates nicely that you don't have to be gigantophagous to grow large. Sufficient and big prey animals were probably common during many periods of geological time, not just one. Small prey is still taken by comparatively large predators, they take a big variety of prey, mostly small animals, and some big ones.
Most aquatic raptorial predators seem to do, including the largest ones we have today.

There is not really a difference between terrestrial and aquatic species in this regard, they all have to find enough nutrition. As with terrestrial animals, it is certainly not obligatory for a big marine predator to have a prey item bigger than itself (neither did Livyatan or Megalodon during the Miocene, and funny enough it doesn't appear there was a significant increase in predator size in the Pliocene, or was there?).

Big prey are at best occasionally taken by most predators. They don't contribute an important part to their diet.


Pliosaurs (McHenry, 2009), or giant ichthyosaurs were never stated to have gigantophagous specialization of any kind, so why compare them to a gigantophagous creature and asume the same ecological requirements, especially since even with that animal tzhese weren't met during its whole reign.

Animals with different ecologies have different needs. And the ecosystems in question offered vast amounts of large prey animals for a big macropredator.


A big predator will usually prey on big animals, unless it's a very specialized form or micropredator. but big does not imply every big predator needs a gigantig prey item, just a sufficient amount of large prey biomass to sustain itself. It's size is only limited by the latter, the former is a loo, variable trend.

[Grey]

What ? The sentence clearly explains that the bigger the preys, the bigger the predator.

If you're specialized at taking the biggest preys (on average bigger and more nutritive given the amout of fat than plesiosaurs and ichthyosaurs), you become bigger here's not even to discuss that. That's just your own personnal wish to get loosely predators as big during the Mesozoic era (which is not impossible but needs evidences and most likely specialization on big preys, which is totally not demonstrated).

No comparison with land animals, McHenry's paper focuses on the size oceanic patterns so let's stay on it.

And let's back to the initial thread subject.

[theropod]

I have the impression you didn't actually get the meaning of what I wrote, but again you seem to believe so. The paper doesn't talk about gigantophagy, actually it states mostly relatively small prey and a wide range of prey size is taken. You don't have to be a giant-prey specialist, and apparently most giant marine predators throughout prehistory wheren't (it also becomes increasingly difficult to find comparatively giant prey if you are a giant yourself...).

Have a look at comparable big oceaic predators today (salties,great whites, orcas), there's an excellent new thread adressing the issue. I think your view of specialisation in big. prey and whether it is required is too simplistic.

Animals get increasingly macrophagous with bigger size, not necessarily gigantophagous (and you can see that among terrestrial animals too, believe it or not. Wolves hunt not just absolutely but also relatively bigger prey than jackals. The same applies to lions and servals. Grizzlies and sun bears. Komodo dragons and perenties...). Yes we can use terrestrial fauna as an analogy, since we have countless good examples here, and they also need to eat.
I never denied the cetacean diversification was among the key factors responsible for the miocene radiation of macropredators. But it's not a unique event in having arguably produced the biggest predators ever, giant predators don't always coexist with the same giant prey and vice versa. there are variable factors that also come to play, such as competition, climate and simply time.

You just have to look at extant orcas and crocodiles (both proposed as analogies for Pliosaur ecology) to see a big predator (in the case of Orcinus, it's a predator reaching the 10t mark) can very well thrive primarily on small prey items. Based on that, countless ecosystems could have easily produced giant predators several times that size, since abundant medium to large-sized prey is far from rare in the history of evolution.

As regards general patrerns, this is a nomenclatural issue, but if exceptions are potentially common we must not overrate their importance.

[creature386]

I thought when comparing Tyrannosaurus with Allosaurus fragilis maximum prey size and not average prey size was meant, sorry.

[theropod]

Well, it was maximum prey size as well as average prey size, just like in the study we have to have a look at the whole scope. And that means maximum or average prey size alone really means nothing.
I think it is not debated that A. fragilis was more gigantophagous than T. rex was (or rather, the latter is actually somewhat specialized in that it is not) and undoubtedly there was a far bigger amount of gigantic prey items available to it, and still, it is the smaller animal. There is no revolutionary point here, just that a predator doesn't need a gigantic prey item to grow huge, but that oppurtunistic (croc-like) predation, at least mostly, on comparatively small prey is also a way of getting huge.

eg. For a pliosaur, this scenario would primarily mean predation on various medium-sized marine reptiles like plesiosaurs and ichthyosaurs (and according to Forrest there's evidence for that in form of bite marks), and perhaps an occasional large planktivorous fish as big as itself. The latter could have happened but certainly it wouldn't have been very important or common.

The same way large predators during the Miocene evidently mainly preyed on comparatively small cetotheres, perhaps with an occasional bigger whale supplementing the diet.

From prey size alone you cannot conclude something precise about the predator, that's where we'd enter the realm of speculation. Especially when we are talking about naturally incomplete, and incompletely known ecosystems. We cannot deduce uniqueness of some event, but rather that an event that occured is evidence for similar events to have occurred.
Sadly our views on these other events are a bit more blurred at now, but what we have of abundant fossil material suggests some extreme faunal radiations to have occured also during the mesozoic. The marine fauna has obviously flourished at multiple ages.

And in the end, if we find a thus-far-unknown giant predator, we always have to take this as a demonstration that we don't yet know its ecosystem well enough to make definitive conclusions, just that there obviously was the prey it needed.

Upper Triassic: teuthophagous Shastasaurs (up to more than 20m) >prey items for Himalayasaurus
lower Jurassic: great radiation in the evolution of plesiosaurs and ichthyosaurs, teuthophagous temnodontosaurs (exceeding 9m) >prey items for unnamed giant Temnodontosaur
Late Middle and Upper Jurassic, lower Cretaceous: Abundant big tunnosaurs (up to 9m, very bulky), cryptoclidids, giant ammonites, big turtles and huge pachycormids (~16m) >prey items for giant Pliosaurs, cardabiodontid sharks in the latter period
Late Cretaceous: Elasmosaurs (some exceeding 14m), giant ammonites, pachycormids (~6m), giant turtles (approaching 5m) >prey items for giant mosasaurs

There is not ONE period of diversification that overshadows all others, every time has brought forth rich ecosystems (eg. GAB during the albian, a crucial phase during teleost and shark radiation. "mr I-know-better-what-you-have-read-than-you-youself"!). Predator size depends on far more than that and has to do with its respective ecology, that is not the same for every predator. A large, oppurtunistic predator like a pliosaur or (likely) Ichthyosaur could, and did evolve during these periods, and reached very big sizes. How big is not very easy to asess, at least 20t, but the ecosystem is not a limiting factor to their sizes.

[Grey]

You definitely exclude that cetotheres were bigger than the vast majority of the plesiosaurs and ichthyosaurs, very abundant and heavily nutritive for meg and Liv, both predators understood to have specialized on whales and occured because of their evolution. Both predators in all likelihood quite bigger than the largest top carnivores represented by pliosaurs and ichthyosaurs.

With the same argument : we don't have found everything.

We obviously all know that, but what counts is what we have. The observation by McHenry is substantial and is not concerned by your skepticism. So I have absolutely and definitely no interest in your reasoning, posts and approach. You're a fanboy who wants big things at any time at any cost. Period.

[creature386]

He actually believes that Megalodon and Livyatan were larger than the cretaceous predators, he only wanted to say that prey size or gigantophagy is not the best way to determine predator size.

I don't know if this is true (I am going to read what McHenry wrote), I just wanted to clarify his point.

[Grey]

The gigantic size of meg and Livyatan is explained because of the evolution, diversification, abundance, size and energetically nutritive nature of their preys. Theropod argues that McHenry (and Kent) are wrong, that others macro-predators could have easily grown bigger than 10-20 tonnes and he sees in these barely studied fragmentary ichthyosaurs these new champions. That's the typical epic lack of cautiousness from him.

I explain him that even if these ichthyosaurs greatly exceeded 20 tonnes (which remains to be demonstrated), does not change this GENERAL pattern, as they could themselves be specialized on contemporary large preys and/or that could only represent an exception. An exception does not change a general trend observed since the history of predation in oceanic macroevolution.

[Grey]

Just watching the Discovery Channel "mockumentary" about megalodon's survival.

I know, almost totally unscientific and so, I only watch it as a quite entertaining fiction, and just looking at the few scientific (interventions of Stephen Godfrey and Brett Kent) or interesting datas.

I've made a screenshot of what appears to be an old news paper appearing in the show :



The measurements are humongous. Few ideas : the newspaper is fake itself (but the 13 000 years old data is not an evidence of fake since erroneous datations have been made with meg teeth), the newspaper is real but the measurements are off, or this is really factual. Sadly we can't get the exact year of it on the pic, but I expect reactions in the paleontological and fossils collectors communities.

I don't know what to think (I've of course mailed Brett Kent), but that obviously reminds me the tooth reported by a guy named Case in the 60's, about a 21 cm tooth.

[Life]

Since two senior members here have not been able to reach a middle ground in a discussion concerning "correlation between gigantism in macropredators and characteristics of their prey," I would like to help in this regard:-

1. Gigantic macropredators prey upon a large variety of animals (ranging from small to large in size aspect); prey preferences (based on size aspect) may vary from species to species.

2. For a gigantic macropredator such as C. megalodon, a large prey item would have been the best option to meet its enormous dietary requirements for a reasonable duration (In this manner, C. megalodon could optimize its hunting preferences; would not have needed to hunt again and again but rather make good choices; sharks are known to learn from their experiences)*

3. Macropredators such as C. megalodon do not exist in huge numbers in comparison to populace of their prey items in any era; otherwise, the ecosystem would not function properly; for every single C. megalodon, their would have been many prey items in existence in any era. In this manner, C. megalodon could afford to go after the largest prey items without penalizing the populace of those animals.

Grey
theropod

Fair enough?

---

*The ground realities of C. carcharias are vastly different from that of C. megalodon in regard to prey preferences.

[theropod]

For me, yes, I fully agree with this ("best, but not only")!

@life: What do you think about mesozoic radiation events by comparison? Doesn't have to be on this topic, it fits nicely on the marine-reptile thread.

[Life]

Aug 5, 2013 16:13:45 GMT 5 theropod said:

For me, yes, I fully agree with this ("best, but not only")!

@life: What do you think about mesozoic radiation events by comparison? Doesn't have to be on this topic, it fits nicely on the marine-reptile thread.

Point to me a relevant thread for this discussion and I would be glad to offer my input.

[theropod]

I meant this one since it deals with giant marine reptiles: theworldofanimals.proboards.com/thread/196/most-powerful-fearsome-predatory-reptile?page=11

Looking forward to seeing your take on this subject. Definitely, I would like to hear a few more opinions on this in general, since it is a subject mostly overlooked.

[Grey]

Explanation from Brett Kent :






In any case, this tooth is world record by modern standards.