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Re: cause of Gigantism in sauropods



That's a great general point.  On a specific level, however, the film of lions 
attacking and killing a relatively healthy adult Loxodonta that I am aware of 
involved about 20 lions lions and a female elephant - so I'll bet that a male 
elephant has well overshot the three-five female lion attack threshold.  Still, 
the general point that pack hunters should be massed as a group is a good one.

--Mike


On Feb 7, 2011, at 3:32 PM, Jaime Headden wrote:

> 
>   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)
> 
> 
> 
> 
> 
> ----------------------------------------
>> 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.
>>>> 
>                                         

Michael Habib
Assistant Professor of Biology
Chatham University
Woodland Road, Pittsburgh PA  15232
Buhl Hall, Room 226A
mhabib@chatham.edu
(443) 280-0181