Re: The Biggest Dinosaurs

[Matt Fraser <mattf+@pitt.edu>]

On 20 Aug 1997, Norton, Patrick wrote:

> If I may expand upon Christy's question for the purposes of this   
> discussion, does anyone have any thoughts about why the upper absolute   
> size of dinosaurs was so much greater than the upper absolute size of   
> terrestrial animals today?  Over the past 5 years or so, I have been   
> (rather informally, I admit--no claim to scientific rigor on this one)   
> compiling references on size estimates of predatory dinosaurs and their   
> probable prey and comparing that relationship to the known sizes of   
> extant terrestrial predators and prey.  From the material I've   
> gathered--which is admittedly sketchy--the *relative* size of predators   
> to prey in those two communities seem to be quite similar, even though   
> the absolute sizes are quite different.

Hmmmm. Interesting.  Many reptiles (and feel free to correct me if I am
wrong, here) continue growing throughout their lives.  Mammals, on the
other hand, more often than not (if not in all cases - Michael Teuton,
where are you?), stop linear growth following sexual maturation.
Epiphyseal closure brought about by gonadal steroids marks the end of
linear growth for these animals.  Now, in order for mammals to attain a
huge size, they must therefore put off sexual maturity for an extended
time.  This puts them at a cost-benefit analysis choice: do I go for size
and risk being killed off prior to reproducing; or do I go for reproducing
at an earlier age. (Of course, growth rates can also vary for species.)

The large size of the Dinos might merely reflect a lack of epiphyseal
closure.  Now here is where the feedback will come in.  Any evidence that
this is true, or to the contrary?

Matt

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