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Re: cause of Gigantism in sauropods



Have you seen this video of an elephant surviving a night attack by eight lions?, http://www.youtube.com/watch?v=djLYqhs2ijw

Jerry Alpern
Ed. Vol., AMNH

----- Original Message ----- From: "Jaime Headden" <qi_leong@hotmail.com>
To: <vultur-10@neo.tamu.edu>; "Dinosaur Mailing List" <dinosaur@usc.edu>
Sent: Monday, February 07, 2011 3:32 PM
Subject: RE: cause of Gigantism in sauropods



We might presume that an adult male *Loxodonta africana* is only as large as it needs to be to be reasonably safe from one to two lions, but not three to five. In other words, it hasn't overshot the predation threshhold because it must account for multi-lion packs (which is how lions hunt). Wolves are similar, as they must predate in a group, making the hunting entity more than an individual, and thus the pressure of the hunter in an ecosystem (unlike a mountain lion or lynx in a similar habitat) is based on the pack/pride.

Cheers,

Jaime A. Headden
The Bite Stuff (site v2)
http://qilong.wordpress.com/

"Innocent, unbiased observation is a myth." --- P.B. Medawar (1969)


"Ever since man first left his cave and met a stranger with a
different language and a new way of looking at things, the human race
has had a dream: to kill him, so we don't have to learn his language or
his new way of looking at things." --- Zapp Brannigan (Beast With a Billion Backs)





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Date: Mon, 7 Feb 2011 09:05:23 -0600
From: vultur-10@neo.tamu.edu
To: dinosaur@usc.edu
Subject: Re: cause of Gigantism in sauropods

>>Another is that many sauropods "overshot": they are far larger than >>required to be effectively immune to predation.

Are they? Even adult African elephants, which are *at least* 20x the mass of lions, are occasionally killed by lions. Lone wolves can kill moose 10-15x heavier. Was any sauropod actually 20x or more heavier than the largest contemporaneous predator?

Well, Amphicoelias fragillimus MIGHT have been... *if* the largest estimates of its size are true, and the larger estimates for Saurophaganax are *not* true.
----- Original Message -----
From: "Michael Habib"
To: "mjohn bois"
Cc: "david marjanovic" , DML@listproc.usc.edu
Sent: Monday, February 7, 2011 8:15:17 AM GMT -06:00 US/Canada Central
Subject: Re: cause of Gigantism in sauropods

I suspect we can all agree that the life history of sauropods and turtles clearly differed in major ways. However, the weakness in your argument below is that there is simply no evidence in the fossil record for parental care of neonate sauropods, and a fair bit of evidence against. As such, while we might be surprised for one reason or the other that they could lay and leave large numbers of eggs, evidence suggests that they did, which implies that it is ecologically feasible. You seem to be suggesting that it just couldn't be true, because you perceive the nests as too vulnerable. In that sense, while I think it's a very interesting concept, I think you may have your test and conclusion flipped.

Personally, I do not find this altogether shocking, because despite your insistence that egg laying is a tremendous risk and liability, a huge number of living vertebrates, some quite large, lay their eggs and abandon them in areas relatively rich with egg predators - but the strategy persists and produces sufficient adults in the end. Not all big turtles lay on remote island beaches, for example.

That said, I agree that the "size is to escape predation" model has notable holes as a single explanatory factor. One if those holes has been mentioned: the time to predation escape was lengthy during growth. Another is that many sauropods "overshot": they are far larger than required to be effectively immune to predation.

Cheers,

--Mike H.


Sent from my iPhone

On Feb 7, 2011, at 8:55 AM, "John Bois"  wrote:

> Some (Loggerheads) in the Sargasso sea. Terrestrial analogue?
>
> And, in general, turtles can't be a good analogue for sauropods.
> 1. They appear out of a completely different medium and so do not
> alert predators. Compare this to a lumbering herd of sauropods
> trekking to nesting grounds.
> 2. Because of water access, they can _and do_ lay in places with
> reduced predation pressure. Can't think of a place Titanosaurs could
> get to that their predators could not.
> 3. Not sure of specifics here but would bet that sauropod eggs' optima
> were more stringent than those of turtles.
>
> On Mon, Feb 7, 2011 at 8:17 AM, David Marjanovic
>  wrote:
>>>> Well, yeah. Enough hatchlings need to conceal themselves quickly
>>>> enough.
>>>
>>> quite difficult, when you need to feed and outgrow your average
>>> cycad thicket. It works for aquatic creatures, but not for
>>> terrestrial ones that grow to several tons before being halfway safe.
>>> :(
>>
>> How actually does it work for sea turtles? It's completely unknown >> where >> they spend their first several years, isn't it? I don't know how to >> hide in
>> the sea while needing to breathe air.
>>