Re: Dinosaur egg-laying contributed to extinction?

[David Marjanovic <david.marjanovic@gmx.at>]

> > Also, many of the birds didn't survive either. We hear no more
> > from the Enantiornithes after the Cretaceous.

Or from any other birds other than Neornithes. That's why the youngest 
known bird tooth comes from the Maastrichtian of Maastricht.

>  And many mammal/cynodont lineages went extinct too, didn't they?

Not quite that many, but several did -- deltatheroidan and stagodontid 
metatherians for instance.

>  Anytime you have such a large disruption of the ecosystem, species
>  will suffer. I think the argument is basically that: Large dinosaurs
>  were more susceptible to ecological disruption - because, due to
>  their large size, they had to pass through multiple ecological niches
>  before reaching maturity. Sub-adults of large dino species filled
>  niches for smaller animals, rather than a new smaller species.
>
>  One ecological niche becomes untenable, a species goes extinct. Other
>  niches that the species filled go vacant, probably causing other
>  extinctions in species that interacted with those now vacant niches.

That's all great, except...

>  I don't see this as an attempt to explain all the extinctions with a
>  single criteria - instead they propose a reason why dinosaurs may
>  have fared so poorly.

But dinosaurs, in particular huge dinosaurs, _didn't_ fare poorly except 
at the K-Pg boundary!

>  A general trend I see, is that those near the top of the food chain
>  go extinct much more often. If dinos were species poor at smaller
>  sizes, that wouldn't bode well for them.

And yet it did for 160 million years.

>  Still, it seems odd to me that more of the smaller dinos didn't live
>  on, even if there were relatively few small species.

Pretty much all those species died out that would be predicted to die 
out in an asteroid impact.

>  I would be inclined to think it has something to do with parental
>  care - and that birds out of necessity had to care for their young
>  better than other dinos, as their young couldn't survive until they
>  were able to fly.

*Confuciusornis* and the Enantiornithes, at a minimum, were apparently 
able to fly at a _very_ young age and did most of their growing later.

>  By the way, is enantiornithine monophly settled, or is there still
>  some doubt?

It was settled around 15 years ago. *Iberomesornis* is a juvenile, if 
that's what you're thinking about.