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Re: Continental predators, etc.
Another thought on "why oviparousness" in birds - the weight! The
average bird has a clutch of four or five eggs. Each one is equivalent to a
significant portion of the parent's mass. Could a passerine get off the
ground carrying so many eggs? Fast enough to elude a cat, fox, hawk or owl?
Instead, birds form an egg and unload it fast in order to maintain thier
flight-worthiness. Eggs among birds are laid one at a time, usually each day
of every other day, in sharp contrast to those of lepidosaurs, turtles and
crocs which complete thier clutches all at once. (personal opinon mine:
dinosaurs probably laid "all-at-once" clutches - at least _most_ dinosaurs.)
The only flighted animal I know of which gives birth to living young is the
bat, which is usually limited to one or at the most two young at a time, and
soon begins to leave the kids in the cave. A litter size this small is
pretty rare among small mammals, and again, I suspect that weight has a lot
to do with it.
Just My $.02 - mostly based on observation and opinion, so take it with
a grain of salt. Or a salt-mine, for those so inclined.