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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" <mjohn.bois@gmail.com> 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
> <david.marjanovic@gmx.at> 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.
>>