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Re: Segregated vs age-mixed sauropod herds

--- On Sun, 3/14/10, John Bois <mjohn.bois@gmail.com> wrote:

> From: John Bois <mjohn.bois@gmail.com>
> Subject: Re: Segregated vs age-mixed sauropod herds
> To: "Dinosaur Mailing List" <dinosaur@usc.edu>
> Date: Sunday, March 14, 2010, 10:52 PM
> On Sun, Mar 14, 2010 at 9:56 PM, Jura
> <pristichampsus@yahoo.com>
> wrote:
> > --- On Sun, 3/14/10, John Bois <mjohn.bois@gmail.com>
> wrote:
> >> sauropods laying eggs was a very big signal to
> >> would-be
> >> predators. Predators must know where the eggs are;
> the nest
> >> must
> >> therefore be defended.
> >
> > +++++++++++++++++++++++++++++++++++++
> >
> > I don't follow. Sea turtle arribadas are also big
> signals to predators, yet those nests go unattended (they
> pretty much have to, given the lifestyle of sea turtles).
> Barring the recent advent of exploitative hominids, this
> strategy seems to work just fine for them.
> Sauropods and their nests were many times bigger than sea
> turtles.
> Many (most?) sea turtles lay their eggs at night--I don't
> know if this
> would be practical for a Titanosaur! 


I don't see why not.


Many of the prime
> nesting sites
> for sea turtles are on islands remote from most
> predators...I don't
> know that any dinosaurs had abilities that would have
> afforded them
> the same separation from their predators. 


While true for some species, arribada species (the Ridleys) nest along 
shorelines in Mexico. Plenty of predators to go around there.


In addition, one
> of the key
> factors in sea turtle hatching success would seem to be the
> massive
> numbers of both mothers and eggs. Aren't they the classic
> example of
> predator-swamping (at least in places where they have
> predators)? Some
> sea turtles have clutches of between 100 and 200 eggs. At
> this rate,
> the ocean would be thick with sea turtles if not for the
> intense
> predation on hatchlings. Such profligate reproduction would
> not be
> possible for sauropods. 


But this is what we see in sauropods. They were r-selected animals. Perhaps 
moreso than most dinosaurs. The auca mahuevo nests also suggest that mass 
nesting occurred in sauropods. While these could have been nests that were 
tended by mothers, they also could have been group gatherings to suitable nest 
sites; done partly to overwhelm would-be predators.


In any case, the trend in amniotes
> seems to be
> toward the evolution of more not less parental investment
> in
> offspring--or, should I say, investment in fewer high
> quality babies.
> This makes nest-guarding more of an imperative.


I'm not sure that such a trend actually exists. Reptile studies (lizard studies 
in particular) seem to show that clades can evolve more, and less parental care 
depending on the situation. This is also seen in crocodylian and avian species 
too (alligators being more attentive mothers than American crocodiles. Cowbirds 
pawning their eggs off for other species to raise etc).

I can definitely see sauropods evolving to be less parental than other 
dinosaurs; likely for the same reason that crocs are still R-strategists 
despite their extensive parental investments. It's very hard for a huge 
multi-tonne parent to guard offspring that are many thousands of times smaller 
than them.