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Re: Combined answer 2 Re: The extinction of small dinosaurs



Original Message by John Bois
Monday, 16 December 2002 00:34

> Date: Fri, 13 Dec 2002 22:27:46 +0100
> From: David Marjanovic <david.marjanovic@gmx.at>
> To: dinosaur@usc.edu
> Subject: Combined answer 2 Re: The extinction of small dinosaurs
>
> > Fish were hurt. We've had that discussion onlist.
>
> I'm curious as to what fossil find you would accept as falsifying the
> bolide--I mean, if fish did swimmingly, despite the energy pyramid being
> knocked from underneath them, this should present a problem.

Apparently it did. And the surviving fish fed on the little surviving 
plankton.

> Yes, tropical species could be restocked
> from places where the post-bolide effects are
> thought to be milder?  Is there a way to falsify this?

Sure. A lot more research all over the globe. Looks to me like very little 
has been done. I suggest a detailed survey of the section in Ellès in Tunisia 
for fish like is has been done for forams. Anyone keen on sponsoring? :-)

> Just to set a base-line...if one known tropical species
> swam right through the K/T, would that do it?

Would depend on a complex array of things... what it ate, how it reproduced 
(planktonic larvae or not, for example), how tolerant it was to changes in pH 
and temperature (hard to tell), how common it was... Anyway, I think one 
species wouldn't do it (though we would definitely have to think about how it 
could have survived!). If it were a lot, then we should think about what 
buffered the effects of the impact(s) so much.

> >> Except for...wait for it...mammals,
> >
> >Remember the diversity of Eutheria before (especially, but not only, in
> Asia) and after, for example. You yourself have talked a lot about the
> metatherian extinctions.
>
> They're not extinct.  We're in a global context, right?

Right. So you haven't remembered... Most known K Eutheria, apparently even 
the "zhelestids", belong to a clade called Asioryctitheria. This clade is 
outside the crown group Placentalia, as shown by e. g. their epipubes and 
narrow pelvic outlets. They're plentiful in the Nemegt Fm (e. g. 
*Zalambdalestes*). There's not one known from the Paleocene.
        Metatheria again and again and again: Campanian-Maastrichtian: 
Deltather-your-favorite-ending-here (may be more basal), Peradectidae (such 
as *Alphadon*), Stagodontidae, Pediomyidae and apparently an exclusively 
Asian clade. Paleocene: Only Peradectidae, maybe one pediomyid in South 
America (the tooth, the whole...), and the clade to which the crown group 
belongs (sister of Pediomyidae).

They aren't extinct as a whole. But more than half of their K diversity is. 
Just like you could say "Amniota is not extinct, so what if anything 
happened".

> >>Raphidioptera
>
> But are you arguing that all insects were restocked from arctic survivors?

No. Because I know much too little about insects. -- Maybe rather mountainous 
than arctic (or antarctic), BTW.

> Or are you saying that every survivor had some sort of acid-rain resistant,
> firestorm-resistant, tsunami-resistant strategy.

Actually... yes. Sure. :-) Firestorms happened, tsunami happened, acid rain 
apparently happened likewise, so... Well, there are beetle larvae that live 
underground for 3 years. Lots of insects spend cold winters in tree bark or 
suchlike (that the tree is alive is not required). Termites live underground 
and can eat dead wood. Ants live underground and can eat pretty much anything 
except dead wood. And so on. Probably a little more interest for the question 
among entomologists will produce a lot more papers like the one on 
Raphidioptera.

(But... of course... there still is random. Tsunami definitely didn't flood 
the whole world. The firestorms may not have reached every last island. It 
may not have rained everywhere within the few months or less in question... 
and much of that is hard to test.)

> Again, how would you know
> you are wrong--what finding would you accept as falsifying the
> bolide-as-cause-for-everything hypothesis?

For example, evidence that the firestorms weren't nearly as global as assumed 
(e. g. from the soot in the global fallout layer) along with a well-supported 
idea about what could possibly have cushioned such a gigantic impact. Yeah, 
there we have it: Show that that thing isn't an impact crater at all and 
explain away all the other evidence for impact(s). That would convince me 
very fast. :o)

Thanks for the ref...

> [A NEW ORNITHURINE BIRD FROM THE MAASTRICHT FORMATION OF BELGIUM:]
> WAS THERE A BOTTLENECK IN AVIAN DIVERSITY AT THE END OF THE CRETACEOUS?
> DYKE, Gareth J., [...]
> ...and it concludes: "Range correlations of lineages of Cretaceous birds,
> combined with gap analysis and the estimation
> of clade confidence intervals shows that there is little evidence for a
> 'bottleneck' in diversity at the K-T boundary."

I don't understand why the authors couple this to the ichthyornithid recently 
described in Naturwissenschaften which weakens their case that "the last 
occurrence of most Mesozoic ornithurine lineages predated the end of this 
Period [sic] by several million years" -- which is negative evidence either 
way. (Would be interesting to know just how old *Potamornis* is -- it's from 
the Lance Fm.) The fossil record of birds stays bad across the K-T, as the 
authors say in their next sentence: "In addition, the oldest specimens 
complete enough to be confidently included within Neornithes are Paleocene in 
age." Which directly counters their standpoint, but again it's negative 
evidence, and it's a bit radical in the presence of *Polarornis*.
        While I don't know the math, I'm sure the "gap analysis" assumes that 
fast 
radiations never happen (as opposed to logarithmic increases in 
diversity...), and that statistics with such low numbers are just not 
reliable. Which is sort of what the last sentence, following the quote you 
gave, says: "More fossil specimens, especially of terminal Maastrichtian age, 
complete enough to be evaluated in a phylogenetic context[,] are required to 
further address this question." Also note that the authors don't support any 
scenario, they just point out that there is little direct evidence for a 
catastrophic extinction among birds and "differential 'survivorship' of 
Neornithes relative to basal ornithurines".

> Again, I'm curious.  Is the hypothesis falsified if an enanti were found in
> the Paleocene?

One might not do it. But in any case a much better knowledge of the fossil 
record is required to tell something decisive. At the moment all that is 
certain is that all Paleocene and younger birds are Neornithes, and that 
other birds were present in the late Maastrichtian. Period. It's just highly 
suspect that this coincides with such a big mass extinction; the most 
parsimonious assumption is that the impact had something to do with it.

> Would it make a difference if it were discovered that these
> birds survived?  Probably not, right?  You would then just set off looking
> for hibernation in enantis,

In this particular enanti. And certainly not for hibernation which doesn't 
leave unequivocal evidence in a skeleton.

Well, find me one, and then we'll see. :-)

> or resort to the idea that the killings were
> random and more neos survived out of luck.

Hm. That it was real pure random is not so likely. But who knows. Maybe the 
last population of 10 enantis was killed off by the last enanti psittacosis 
virus. Untestable but not impossible.

> >There is a fern spike in the USA, New Zealand and
> >Hokkaido.
>
> This hurts.  I'm tempted to cry uncle.  But, how does this affect your bird
> refugium hypothesis.

"Mine"? It's by no means my idea. It's in several SVP abstracts, for example.

> If the atmosphere was just as toxic in the south, how
> did birds survive it?

We'll need more research in Antarctica (which is, after all, not that 
easy...). Anyway, the pyrotoxins won't be a long-term problem if it rains. 
The fire itself and the resulting habitat destruction should be the main 
killing agents in a global wildfire.

> >Maybe everywhere else all birds were killed, and in Antarctica a
> >few that happened to be neos managed to survive.
>
> That must be it.

Maybe it was. :-|

> Bats are probably susceptible
> to predation by diurnal flying things (birds).

Definitely the other way around. False vampires attack sleeping birds.

> _And_ because they don't
> need a flat surface to put an egg, they are not in competition with birds
> for (particularly) caves.

The only known pterosaur nesting site is in a paleodesert. Plenty of space 
there. Really. :-)

> Pterosaurs went head to head with birds.

Then _why_ don't birds today go head to head with one another?!?

> I believe birds were the superior competitor.  It's _OK_ to be
> superior.

But it's _not_ OK that you believe birds were superior just because they 
survived. Really not. :-)

Original Message by John Bois
Monday, 16 December 2002 03:37

> Birds lived with pterosaurs.  They likely shared some niche requirements,
> but not others.  A bird species may have lived a completely separate life
> until nesting season when it needed the rock ledge occupied by a pterosaur.
> This particular bird, and several of its mates, kept swooping on the
> hapless pterosaur until it flew off.

Those mates won't do anything of the sort unless _perhaps_ if the rock ledge 
is big enough for them all. Why should they devote _their_ energy to 
_another's_ reproduction? What do they get from it? If the place isn't big 
enough, then they'll all quarrel with one another, including the pterosaur. 
"Hapless"? With teeth and wing claws... ~:-|

I'm pretty sure this will lead to niche partitioning pretty fast.

And then, who says all pterosaurs nested on limited ground. AFAIK there's no 
evidence for cliffs around the Western Interior Seaway. Do birds today fight 
for nesting sites? I've never seen this on TV or read about it. Has someone 
else?

I can ask the other way around: Show me that e. g. the Cenomanian-Turonian 
mass extinction had nothing to do with it. You'd need a lot more fossils of 
pterosaurs and birds for this.