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Re: Protungulatum index; pterosaur finger.



----- Original Message -----
From: "John Bois" <jbois@umd5.umd.edu>
Sent: Friday, July 12, 2002 6:08 PM

> > why should these same
> > birds have done in Enantiornithes plus the giant pterosaurs _50 million
> > years later_?
>
> I thought the story of pterosaur disappearance was: toward the end of the
> Cretaceous species got larger and rarer.

Larger... well... not gradually... throughout the Maastrichtian only
Azhdarchidae was left as far as is known, in the IIRC Campanian only
Azhdarchidae, Nyctosauridae and Pteranodontidae, and I don't remember when
this condition started, maybe after the Cenomanian. Some Campanian
azhdarchids were _relatively_ small, though; *Montanazhdarcho minor* had
just 2.5 m wingspan. Anurognathidae isn't known after *Dendrorhynchoides*
and *Jeholopterus*; Pterodactylidae-or-whatever likewise stops with
*Eosipterus* if we can trust our current knowledge of the fossil record;
*Dsungaripterus* (4 m IIRC?) is something like Albian; I'll look for some
literature.
        So at present it looks like the small pterosaurs outside
Azhdarchidae died out something like 50 Ma before the big ones. Can hardly
have had the same cause IMHO.
        Rarer? IIRC *Quetzalcoatlus*, *Arambourgiania*, *Hatzegopteryx* and
the still-unnamed Spanish giant form are all Maastrichtian. The last two are
end-Maastrichtian in any case.

> In any case, one possibility is,
> re giant pterosaurs, that they used their long range capacity to distance
> themselves from their predators [...]
> This may have changed with the advent of--wild speculation both in
> idea and spelling--frigitiiforms.

You know, this is a testable hypothesis. Currently frigatebirds* start with
Limnofregatidae in the Paleocene (the allegedly K limnofregatid *Volgavis*
is Paleocene, as was mentioned onlist). Find a K frigatebird. Then find
evidence that frigatebirds are dangerous nest predators (AFAIK they
specialize in other activities today). If you can't do the latter, find a
way how a teeny weeny frigatebird can have endangered a pterosaur with a
wingspan 6 times and more of its own, and this fast enough that the
pterosaurs can't even evolve a behavior to stop them (that the pterosaurs
will evolve is likely in such a scenario because the selectionary pressure
would be very high). If you succeed in all this, then you must still show
that the frigatebirds and not the impact did it. For example, evidence for
fast but gradual extinction of pterosaurs would help; it would be easiest
but not absolutely necessary if you'd show that pterosaur extinction didn't
coincide with the impact. Only after all these procedures, which involve
lots of fossils we don't have yet, does it start to become interesting.
        If _any_ of these steps fails, then your hypothesis is guilty until
proven innocent. Or until all alternatives are falsified.

* Traditionally in Pelecaniformes. Molecular studies have dissolved
Pelecaniformes without proposing a clear alternative. The radiation of
Neognathae must have happened _very fast_.

> Or, maybe birds, mammals, and dinosaurs
> took care of the rest and the bolide slammed the last few biggies.

How is this different, especially in testability, from "just like almost
everything, they had nest predators, but it took an impact to make them
extinct"?

> > It doesn't look like pterosaurs and birds
> > competed, unlike insectivorous bats and insectivorous birds that would
> > compete if they weren't segregated by time.
>
> Side issue hypothesis: birds and bats

_Some_ birds and _some_ bats, not Neornithes and Chiroptera as a whole. Many
fruitbats aren't so strictly nocturnal AFAIK.

> are highly competitive (after all, as
> you say, they often eat the same things).  But birds have outcompeted bats
> by day, and bats, birds, by night [...].
> This is either as a result of an arms race between sensory systems--acuity
> of vision in birds v. echolocation in bats, or, and this is my feeling,
> birds can survive in the diurnal predatory environment whereas bats
cannot.

May amount to semantics, but I'd rather say "competitive exclusion": birds
started as diurnal animals and simply didn't get nocturnal (before bats
evolved at least), but bats (as mammals) started as nocturnal animals and
were unable to get diurnal because during the day there were too many
insectivorous birds that ate their food. Predation? There is a bat species
(is it the false vampire?) that more often than not eats sleeping birds. Not
to mention the owls at night. And I repeat that bats are more maneuverable,
so they should escape birds of prey _easier_ than birds.

Another explanation, from Pat Shipman: Taking Wing: Bats get sunburn much
too easily, and bats with heavy sunburn on their wings (a specific example
is mentioned) can't fly. Don't know if that holds for all bats (after all,
bat wings are frequently dark brown to black).

> > > There must be some science on this: how big must a juvenile feathered
> > > creatured be relative to a non-feathered juvenile?
> >
> > What effect should age have here?
>
> Adult airframes are more aerodynamic.  Creatures start out as balls and
> extend in the periphery.  Balls can be thrown, they cannot fly--in this
> universe at least.

But... creatures that grow fast and extend in the periphery before they
start to fly are totally freed from this problem. No remotely ball-shaped
pterosaur is known, despite lots of juvenile specimens.

> > I mean, even when rheas were in danger throughout their lives, not just
as
> > eggs and young, they didn't die out. Now the adults are pretty safe,
> aren't
> > they, so their situation has already been worse?
>
> First, I don't think modern aspect rheas are known from (Miocene?) those
> times.

I can cite literature (later if needed) about Eocene rheas of apparently
modern size, whatever else "modern aspect" means.

> And, until recently, they have been subjected to predatory
> mammals--jaguars, right?

<sigh> Wrong. Jaguars are ambushers _in the jungle hundreds of km away from
the pampa!_ I know many stories in which "the lion" is called "the King of
the Desert" or is put into a jungle. But I really didn't expect such a
phenomenon onlist.

> Interesting that they suffer
> horrible nest loss from armadillos burrowing under nest, nest collapses,
> armadillos run off with eggs!

Why interesting? They just lay even more eggs than are eaten. Simple
r-strategy. :-|

> > > Pterosaurs are elegant and speedy walkers compared to what?
> >
> > Penguins. Albatrosses. Maybe even ducks.
>
> Irrelephant!  They site nests in places where defense is not necessary,

I'll look up the paper. -- You have seen a duck run, haven't you?

> i.e., heavy cover or in areas of low predator density.  Was this possible
> for late K pterosaurs?  Remote nesting was probably the only available
> strategy for them. So...

So what? Maybe that was just what they did. There always were islands, if
you want such extreme protection. Of course there are other strategies, such
as colony nesting and defense (just imagine how big a *Quetzalcoatlus* beak
was).

> > > > > --must watch their babies more carefully.
> > > >
> > > > Maybe they did :-)
> > >
> > > All egg layers must.
> >
> > Many don't. Turtles for instance.
>
> Turtle hatchlings require no parental investement after laying.

Just meant that your exact wording "all egg layers must" is wrong.

> As such
> they are irrelevant to this discussion--unless you're arguing no parental
> investment for pterosaurs--which is possible, I suppose--

No idea.

> sounds like free eggs breakfast, though.

Again no idea. Next wild speculation -- they buried their eggs just like sea
turtles. I don't think they did, but who knows.

> Please don't drag me into egg discussion.

Not sure what you mean, but no pterosaur eggs are known at all.

> > So do you consider this specific example falsified?
>
> No, my whole point is that neornithines had some edge on enantiornithines.

It is simply impossible to compare neornithines as a whole to
enantiornithines as a whole, because both groups included members with
wildly different ecological niches. Or where am I wrong here?

> This case supports me: Boluochia was a great bird but not as great as
> hypothesized neornithine falconiforms.

It doesn't support you at all. Unless you can tell us why *B.* wasn't great
enough, and that K falconiforms existed!

> If it had knocked out all
> pterosaurs, I would be falsified, no?

Assuming I've understood what you wrote so far:
If it had and if we had found that out, we would know that birds could and
did outcompete pterosaurs, which is the point on which you try to build that
neos outcompeted enantis next (and what about Ichthyornithiformes and
Hesperornithiformes...). Right? Because we know that *B.* didn't do it,
while in the current form of your speculation every bird of prey should be
able to do it, you must do what I wrote above: show why *B.* couldn't have
done it while falconiforms could have done it, and that K falconiforms
existed (fossils). (Taking a robust phylogeny that shows, via phylogenetic
bracketing, that falconiforms must have existed would not be enough, because
who tells us then when falconiforms started to actually be birds of prey.)
        Similar to the peculiar inability of *Repenomamus* to hurt anything
with its jaws the size of a dog's, methinks. :->

Everyone else, don't worry, I'll be with my grandparents for two weeks from
Sunday on, far away from any computer :-)