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Re: Protungulatum index; pterosaur finger.




On Thu, 11 Jul 2002, David Marjanovic wrote:

> > by smaller pterosaurs
> 
> Actually... I thought we were talking of how the very last pterosaurs, all
> of which were, as far as known to date, gigantic azhdarchids, died out. --
> Few really small adult pterosaurs are known. Adult *Rhamphorhynchus* and
> *Pterodactylus* reached over 2 m wingspan.

No, I think we are talking about the long decline including the
denumen--why did small pterosaurs disappear?  It's a worthy question.  If
specific birds did it, then these same birds may well have had an effect
on other bird competitors.

> > would be unlikely
> > because feathers confer greater manueverability to creatures of equal size
> > (therefore, larger birds could be just as--or more--manueverable as
> smaller
> > pterosaurs)
> 
> Wrong. According to DA the cambered wings of bats give them the great
> maneuverability necessary for hunting insects on the wing.

Right.  But pterosaurs had fewer adjustable wing surfaces, right--one
finger, primarily (unless all the fossils morphed since Romer was writing
back in the Jurassic).

> > - just as bats are banished (largely) from the day niche by birds, the
> even less effective pterosaur fliers would be prey to Cretaceous
> >equivalents (if any existed!)--predation is the key, here
> 
> Just as passerines keep albatrosses from flying during the day -- oops...

How does this relate?

> > -baby pterosaurs must be nurtured for longer than baby birds because they
> > are heavier and develop less thrust than baby pterosaurs (going out on a
> > speculative limb here).
> 
> So speculative that I needn't even answer IMHO. Why "less thrust"?
> Azhdarchids had powerful flapping abilities.

There must be some science on this: how big must a juvenile feathered
creatured be relative to a non-feathered juvenile?  I don't see why this
should be speculative.  It's as if there is no value at all to
feathers--which is why I asked the question in the first place.

> > This additional PI costs
> 
> What's that? I don't understand it even if I fill in "*Protungulatum*
> index".

Ha!  Sorry--no excuse, I hate it when people do that.  Parental
Investment.

> attack
> > and kill the hawk except that it just flies away...waiting for the rifght
> > moment it snatches the less agile parent's chick and flies off with
> > impunity.
> 
> You're forgetting that
> 1. rheas still aren't extinct. Even though for most of the Cenozoic there
> were predators that were able to run after them -- phorusracoids.

Rheas better hiders than terror birds--remember, running _away_ doesn't
really help when you're trying to guard chicks.  But, defending an errant
chick against a predator smaller than you, it might help to rush the
predator.  I am certain that the rhea gets around much more effectively on
land than pterosaurs.

> > Hoplelessly clumsy pterosaur walkers--
> 
> Wrong. There was a beautiful paper on the tracks called *Pteraichnus* --
> pterosaurs were pretty fast and elegant walkers. -- You're assuming that
> azhdarchids nested on the ground. Is any evidence for or against known?

Pterosaurs are elegant and speedy walkers compared to what?

> > --must watch their babies more carefully.
> 
> Maybe they did :-)

All egg layers must.

> One more question: Why didn't *Boluochia*, a real fossil falconiform-mimic
> bird, take over the world in the mid-EK?

No idea.  And I'm not arguing that one bird--the falconiform if it
existed--took over the world.  I'm only using it as an example.  I'm
arguing that there is a relationship between pterosaur
extinction and bird evolution.  This is not a stretch (though, of course,
it may not have happened).  If birds influenced the success of other
flying forms, there is a chance they also influenced the success of their
own clades.  But, perhaps it's possible that aerodynamic formulae can be
informative on the difference between feathered and skin wings.