Re: Sheesh

[Jamie Stearns <stearns5@cox.net>]

> Why have no birds, or indeed -as far as is known- archosaurs (sensu sort 
> of
> traditional) never got around to giving birth to live young (sensu any way
> anybody chooses)?  Bearing that latter proviso in mind, some sharks, fish
> (sensu very loose indeed), frogs, reptiles of various persausions (or
> sauropsoids), scorpions...  Various lineages have manged this, but
> archosaurs seem uninterested in such experiments.
>
> My suspicion is that the hard and potentially sharp eggshell shards may be 
> a
> discouragement, but it's no more than a suspicion.

As I recall, sauropterygians are considered to be archosaurs (correct me if 
I'm wrong here) and ichthyosaurs managed to give live birth well enough.

As for dinosaurs giving live birth, I've heard it suggested once that the 
hip structure of Homalocephale may have been designed for such a purpose, 
but was subsequently explained away as more of a way to sustain the shock of 
butting heads. However, now that the head-butting theory is falling apart, 
it's possible the previous explanation could have some merit to it. I don't 
recall much mention of marginocephalian eggs anymore now that the 
Protoceratops eggs have for the most part been reassigned to oviraptorids.