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Re: Segregated vs age-mixed sauropod herds
I am thinking of very broad trends: animal body plans and strategies
evolving most recently indicate higher parental investment:
placentals compared to monotremes; birds compared to basal dinosaurs;
archosaurs compared to lizards. Indeed, the amniotic egg itself is a
quantum leap in investment compared to amphibian reproduction. Is
this scale too broad to be useful?
Apparently the amniotic egg cannot be gotten rid of once it's there,
unless we count viviparity (...where the chorion, amnion, and allantois
are still not lost -- only the eggshell and the yolk are, basically).
But both amniotic eggs and viviparity still allow fairly large
Among squamates, reversals from at least ovoviviparity to oviparity seem
to have happened a couple of times.
"Amphibian reproduction"... most salamanders have quasi-internal
fertilization (with a spermatophore), and there are direct-developing
salamanders and frogs, and plenty of viviparous caecilians. There are
even salamanders that secondarily reacquired the free larval stage
("direct development" means that the larval stage is passed in the egg,
and the resulting foetus lacks larval adaptations, simplifying its
development; the hatchlings look like adults).
I don't say this is any kind of rule like voodoo Cope's Rule...more a
I don't see the difference between those.
On Mon, Mar 15, 2010 at 5:36 PM, John Bois <firstname.lastname@example.org>
> I am thinking of very broad trends: animal body plans and
> strategies evolving most recently indicate higher parental
> investment: placentals compared to monotremes;
Isn't it quite possible that Monotremata and Placentalia (crown
clades) are around the same age?
Monotremata could even be a lot younger. But egg-laying isn't.
> birds compared to basal dinosaurs;
What do we know about parental care in basal dinosaurs? (By "basal"
I'm assuming something like "pre-Late Jurassic"?)
Just about nothing...
> archosaurs compared to lizards.
Aren't the earliest squamate fossils Jurassic?
Yes, and the earliest lepidosaur fossils are Late Triassic (Carnian),
IIRC. The reproduction of other diapsids, apart from sauropterygians and
ichthyosaurs, is unknown.
On Sun, Mar 14, 2010 at 11:50 PM, Jura <email@example.com>
> Reptile studies (lizard studies in particular) seem to show that
> clades can evolve more, and less parental care depending on the
But you don't see lizards setting up creches (ostriches), arranging
multi-generational nest provisioning (crows), guarding offspring
through different growth phases (alligators), or teaching their young
how to compete in the global economy (community college adjunct
professors)...I'm saying that there are small differences among
clades, big differences between clades, and increasing complexity and
flexibility among clades with larger brains...and that this
potential goes to titanosaurs more than sea turtles.
I think there's _more diversity_ in clades with whatever "larger brains"