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Long, long last gasp.
Jaime Headden says:
> The collected and observed trend would lend credence to an idea that
birds were filling the small flier niches, and pterosaurs dominated the
large fliers. But there does not seem to be a marked increase in large
birds known that would have removed the azhdarchids and pteranodontids
from the picture, as both seem to have survived into the upper Campanian
and some through the Maastrichtian, this without a well-represented
selection of bird-laden beds to compare to. So I don't think the evidence
currently favors pterosaur/bird competition to explain absence of
diversity in either group, or the forced extinction of one or some
Competition is not limited to species beating each other to the food
trough. For barnacles it might be a relative inability to cope with
desiccation. And, for pterosaurs, it might have been a relative
inability, relative to birds, to cope with predation. So, absence of
large birds is not necessarily important for the competition hypothesis.
> One could easily attempt to use this diversity through the Cretaceous
as a means to explain enantiornithine extinction, as much as pterosaur
extinction, prior to the K/T event.
Yes! If and when this is ever established, this would remove two very
important members from the body count.
Chris Bennett says:
> I have argued...that large pterodactyloids like Pteranodon were
altricial and like many extant birds stayed "in the nest" and relied on
parental feeding until they grew to virtually adult size, whereupon they
would leave the nest and begin flying and feeding independently.
For large oviparous animals this is suggestive of remote nesting sites
with little or no predation-compare with precocial ratite chicks growing
up amid predators.
Jonas Weselake-George says:
>...given that most pterosaurs were apparently quadrupedal and many of
them would probably have had a bird like metabolism, being trapped on the
ground for even a few days could wipe out a species (especially if there
were other pressures).
Not if this species were wide ranging, and could wait it out on a remote
island somewhere. Would a local event kill all albatrosses. Or, are the
skies and ground perturbed globally in such a way that birds survive and
>Think of the advantage the heavily insolated running bird has in hunting
on the ground compared to a pterosaurs delicate quadrupedal movement.
I think this supports my contention that birds could handle themselves
much better on the ground than pterosaurs (not that Jonas is arguing
against that). By the way, how fantastic is it that some terrestrial
birds are immune to the world's nastiest, fastest predators. Ostriches
foil predators that gazelles cannot.
Tim Williams says:
>...the corpus of fossil evidence suggests that the Neornithes were by no
means the dominant avian lineage in the later Cretaceous. On the
contrary, the neornithines were Cretaceous 'oddballs'.
In the latest sally for molecules v. fossils, a recent mammal fossil find
(reported in a recent Science extended their evolution backward to the
molecular estimates. We are missing fossils. This doesn't contradict
your statement. However, it reduces its confidence level. Neornithines
may well have outcompeted Enantiornithines
> this does not disprove (or even undermine) the occurrence of a global
catastrophe of extraterrestrial origin. It is obvious that many lineages
hit a wall at the K/T - including the non-avian dinosaurs.
The effect on _species_ is a hypothesis. Expressions of confidence are
OK. Explanations are better. How did modern birds survive those days when
other birds with (probably) many similar niche requirements and morphologies
>pterosaurs had a very considerable head start for feeding
specializations and a fundamentally different mode of flying; it's not
clear that there would be direct competition for food, or that early
birds could reasonably expect to compete with pterosaurs for food at all.
Food that different modes of flying made available to birds that wasn't
available to pterosaurs wouldn't have been part of the pterosaurian diet
in the first place
I agree with this but it doesn't address the predation proviso for
T. Michael Keesey says:
>It's interesting that today's two large clades of flying animals
(_Neornithes_ and _Chiroptera_) largely avoid competition by being awake
at different times.
They're probably not avoiding head to head competition for food. Bats
are more likely avoiding getting whacked in the day light. This still
makes birds the better daytime species.
James R. Cunningham says:
>Why not start with the opposite hypothesis, that the birds were
different in a way that led to an avian deficit on land? Or in the air,
I'm not particular. Either way, you can then attempt to falsify the
hypothesis and see where it leads.
OK. For starters: birds are descended way more recently from terrestrial
animals than pterosaurs. Birds get around well on the ground. I can't
imagine a secondarily flightless pterosaur (or bat-is such a thing
known?)-I would guess that the adaptations required for bat and pterosaur
flight preclude secondary flightlessness. Can I get a witness on this?
Is it relevant? I'm not denying the pterosaurs grace or agility, just
that their limbs have been too distantly co-opted for flight.
David Marjanovic says:
>Either we have next to no idea at all about what happens when a mountain
falls from the sky. Or the impact produced lots of bad flying weather.
Is this a trick question? The former. I could buy that there is an
understanding of the local effects. But it's a huge stretch to predict
polar weather, global climate change, daily flying conditions, etc. In my
view physical scientists ought to take a cold shower before they start
declaiming about effects on the biota.
>Why should this evolution have taken place during the existence of Q,
and not 50 Ma earlier? Even *Ichthyornis* is 15 Ma older than Q.
It must have happened then, because that's when Q became extinct
(bolide-thinking, as in: Q must have gone down in bad flying weather
because that's when the bolide hit).
>> And then my impression is that birds are able to
>> compact themselves more than pterosaurs--
>How do you mean?
I was thinking that a bird's wings present an invisible profile when not
in use. A pterosaurs wing has bits sticking out. Is this true?
>Oh, this _still_ doesn't tell us how Djadochtatheria (Multituberculata)
and Asioryctitheria (Eutheria, e. g. Zalambdalestidae and Zhelestidae)
died out -- Zhelestidae seems to have occurred even in Madagascar (that's
where the "marsupial" tooth from there is now put). These groups are not
known from North America or any place with a good record of the late
Maastrichtian (and early Paleocene).
>> And marsupials _may_ have been impacted by invasions and should not
be included in the body count.
>First I'd like to see a) good dates for the invasions and b) evidence
that the invaders _could_ have competed with the present fauna. To
suggest that *Protungulatum* competed with *Didelphodon* or *Pediomys* is
like saying a fox/duiker/pig/beastie is going to compete with Tassie
devils or shrews. Yet Stagodontidae (*Stagodon* is a junior synonym of
*Didelphodon*) and Pediomyidae are the 2 metatherian groups of North
America that went extinct at the boundary (the third, Peradectidae, to
which *Alphadon* belongs, survived until the late Miocene).
Yet when faunal interchanges occur species become extinct.
>If metatheres are all you want to remove... those forams and haptophytes were
>quite speciose... ammonites... plesiosaurs... mosasaurs... non-neornithean
>dinos... that would still look suspiciously like a catastrophic mass extinction
I want to remove marsupials, pterosaurs, ammonites seem to have suffered a
Cretaceous-long decline, and they may have affected mosasaurs. Dinosaurs seem
to have been in a similar state as pterosaurs, i.e., losing considerable