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Re: cause of Gigantism in sauropods



> What I find for sauropodomorphs in general and for sauropods in
> particular is passive expansion of the size range, followed by
> extinction of the small members. This is different from a driven
> trend.

 Different in what way?

Driven trend: descendants are larger than their ancestors throughout, at any level of detail (it's fractal). Passive trend: descendants evolve in random directions, and then something takes the small ones out.

The long-term outcome is the same (you start with small organisms and get large ones); the mechanisms are completely different. This is explained very well in S. J. Gould's book Full House.

That book also explains two more possibilities that need to be ruled out first: Expansion with lower limit: descendants evolve in random directions, except that there is a lower limit, so the descendants of ancestors that are at the lower limit cannot be smaller. Unconstrained expansion: descendants evolve in random directions, and people concentrate on the biggest ones and ignore the rest.

 And then who and what conceals the hatchlings? Oh, sea turtles do
 have a certain predation pressure problem right there......

Well, yeah. Enough hatchlings need to conceal themselves quickly enough.