[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

Re: Late night thoughts: Pathetica and Irony

1). Your "hypothesis" is, you state, that for predator driven size selection
(size race) to be shown within a given population, minimum size must increase as well
as maximum size. That is absolutely incorrect within groups composed of more than
one species. Barring sample bias or data error, if minimum size and maximum size
_both_ increase, it is symptomatic of a selective regime in place that is affecting all
animals within the group, such as an environmental factor or an illusory uber-factor like
Cope's Rule. Relative to minimum size, it is the exact opposite pattern expected from
a predator-driven size trend in a multiple species population.

Not at all: if all species of such a group are potential prey -- this is what defines the group --, and if all of them can only escape by growing, then all will grow or die out.

See here http://www.dinosauria.com/jdp/evol/evolfact.htm for the meaning of words like "hypothesis" and "theory".

When predator pressure occurs on a multi-species group of the size
(species-wise) and time-frames considered here, some elements inevitably find
refugia from the pressure, whether the refugia is environmental, geographical, or biological.
Adaptation to refugia frequently involves size change, including size decrease.

Size decrease is not what you or I would recommend to a sauropod as an adaptation to predation pressure! Except maybe if it's armored, but only lithostrotians are armored.

Your statements are tantamount to insisting that in order for predation to
affect size, predation and ONLY predation can be operating, and the predation
pressure must affect all the potential prey organisms equally across the board.
This is simplistic, and ignores the fact that probability, and therefore
selective vectors, are additive.

Again: are you saying your hypothesis is not testable? I hope you're not saying that.

2). Hone's study, that you so flippantly cite, was testing Cope's Rule. OF
Perhaps Hone will weigh in on whether he thinks predator pressure had anything to do
with the size of the mega-sauropods... or whether sauropod size affected the size of
any of the maximal meat-eating theropods.

Reality check again: not only does the minimum size not increase in sauropods, neither does the average size, and neither does the maximum size. You predict an increase of at the very least the maximum size of sauropods and theropods; the biggest LK sauropods are about the same size as the biggest EK sauropods, the biggest LJ sauropods except the much larger *Amphicoelias fragillimus*, and the biggest MJ sauropods (judging from tracks); the biggest LK tberopods are about the same size as the biggest EK theropods and the biggest LJ theropods; your prediction is falsified.

3). Patterns found by Carrano evidently support the thesis
of predator pressure and perhaps even a 'predators won'
picture (I hasten to add I do not know of him advancing
that idea or expressing any opinion on it). To paraphrase,
the big sauropods 'sputtered out at the end', and size
decrease in sauropods 'signaled the end of the lineage'. Note
the post-Mid-Jurassic giants that just disappeared. A 'scientific'
skeptic may argue the neutrality of the evidence, the fossil record
clearly does not falsify the concept of predator-driven size selection
among sauropods.

Sure it does, according to my results and those of Hone et al.. Carrano (2005) even found a _decrease_ of sauropod size, which is the _opposite_ of what you predict (though this may be because he used several immature specimens).

4). I thought you would retract, but evidently you stand by this statement;

DM -- "And then there's, again, the fact that neither minimum nor
maximum nor average sauropod (or even sauropodomorph) size increased
across the Mesozoic. Your hypothesis says they did grow bigger, the
fossil record says they didn't, your hypothesis loses. Am I missing

What you are missing with me at this point is credibility.

No wonder. My M. Sc. thesis isn't published yet, so I can't prove that I really get the results I claim to get. I fear you'll just have to trust me on that for something like a year.

Except for a bit of sauropodomorph data. In his redescription of *Anchisaurus* as a sauropod Yates (2004) found a size increase in a sample of femoral lengths of early sauropodomorphs; I am currently (as the 2nd author) working on a paper that takes the same sample and the same phylogeny, adds branch lengths, and finds that there was no size increase. (Yates used MacClade, which cannot help assuming that all branches have the same length; we use Mesquite http://mesquiteproject.org, which can deal with branch lengths; Mesquite didn't exist yet when Yates worked on his paper.) But of course the sample is incomplete and the phylogeny is outdated (according to Yates's own more recent results). We'll probably submit this paper soon, so it should be out in maybe half a year.

Do you want me to spell out the references, or have you got all the papers I mention?

First, it is not my hypothesis; this is the first time I have heard
anyone with any knowledge of evolutionary theory dismiss the
idea that the mega-sauropods weren't driven at least to some
degree by predation.

Yes, but till 2 or 3 years ago it was not possible to test this hypothesis. Most notably, Mesquite didn't exist yet. And no, you are the first who gives such prominence to predation pressure as to postulate an arms race; earlier versions typically assume the sauropods won very quickly and were, when adult, too big to be attacked by anything.

'Predators won' has also been advanced many times, I would bet.

Never, because that would mean sauropod extinction.

It has been, in fact, consensus that they "got so big to avoid predation, so they could be invulnerable" for over a 100 years, right?

"Consensus" is exaggerated, but yes, the idea used to be widespread, and no, it was never tested or even testable until recently, and no, it was assumed that the sauropods _won_ and that adult sauropods actually _were_ invulnerable, and no, the data completely disagree with any of these ideas. When the data contradict even a century-long consensus (which we don't have here), the consensus loses. That's called science. It sometimes gives counterintuitive results.


I have tried to show you what predictions _inevitably_ follow from your hypothesis, and that all of them are falsified. You get emotional and start shouting.

Second, the statement that maximum sauropod size didn't increase "across the Mesozoic" is so bizarre I strongly suspect you are pranking me.

When I make a joke, it's like: "Why do elephants have red eyes?" -- "So they can hide in the cherry tree."

No, my friend. Show me that *Puertasaurus* was bigger than *Argentinosaurus* -- hint: _nobody has ever claimed that this was the case_. We don't even need to take the Late Jurassic *Amphicoelias fragillimus* into account. Where are you getting your basic assumptions from!?!

And then let's wait for the SVP meeting of 2008 when new material of *Amphicoelias fragillimus* will be introduced.

Sum-- If you think there are Triassic giants out there, go find one.

That's not even what I said: I said that there is a wide size range in the Triassic, and that this range increases at both ends in the Early Jurassic, and then more or less stays the same from the Middle Jurassic through the Late Cretaceous. An analysis that takes the phylogeny, and not just the stratigraphy, into account shows that there was no size increase in sauropods across the Mesozoic. Period.

As to average size, it is not relevant above the level of species, due to
the confounding effects of refugia. Not to mention being so subject to
sample and measurement error as to be laughable. Minimum size has
meaning, _perhaps_, but not the one you ascribe to it.

Confront a small sauropod (say *Amargasaurus*) with a very big theropod (say *Giganotosaurus*). Assume (as you do) that the theropod can, with a very high success rate, kill the sauropod by sneaking up and biting it in the neck. What is the logical outcome?

Confront a middle-sized sauropod (say *Camarasaurus*) with a very big theropod (say *Saurophaganax*). Same assumptions. Now take into account that *A.* has these scary neck spines, but *C.* doesn't. What is the logical outcome? Not the fact that *C.* is the most common fossil in the Morrison Formation.

Logical conclusion: something must be wrong with the assumptions.

You said "let's end this one here". That is fine with me. I want to spend
my time on things relevant to hunting strategies, and important stuff like
how long could a sauropod hold it's breath, and I much prefer chess to
tennis anyway.. If you reply to this post, DO NOT DELETE ANYTHING.
And don't intersperse, please. Clear a space above or below, and leave my
words intact so people HAVE to know what I said, and I don't have to say
it again. Thank you! -- Don

- Your e-mail has been sent to the list, so everyone who wants to can read your words in the original; those people are interested know full well what you have said. Whether they've understood it is another matter, but not one I could influence!
- I have of course interspersed. This makes sure I don't overlook any of your arguments, and it makes sure that people can read your arguments and my responses together. I don't understand how you can get so worked up by this.
- I always leave an empty line between your writing and mine, in case you haven't noticed! I also make sure that each quote in each e-mail of mine is preceded by a ">" when the program doesn't do that automatically. I'm sure you've noticed that, too.