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Re: From Science New, and synonymous sauropods




From: David Marjanovic <david.marjanovic@gmx.at>
Reply-To: david.marjanovic@gmx.at
To: dinosaur@usc.edu
Subject: Re: From Science New, and synonymous sauropods
Date: Mon, 11 Nov 2002 23:01:14 +0100

Original Message by Tim Donovan Monday, 11. November 2002 13:19

> >On Sun, 10 Nov 2002, John Bois wrote:
>
> > I only meant to say that the study of dinosaurs is appropriate
> >(for all we know) for the the study of dinosaur's extinction


It is of course not totally irrelevant, because it contributes to the whole
picture. But it alone cannot replace the rest of the whole picture. After
all, not only dinosaurs died out; dinos made up a pretty small percentage of
the victims.

But they were ecologically very important; their extinction could have had repercussions affecting many others in various ways.

> Note the loss of some diversity about 2 million years before the > end, which suggests another factor causing a preliminary extinction.

Some have suggested that there was a little mass extinction in the
mid-Maastrichtian, totally unconnected to the K-T. I don't have enough
literature on it.

Diversity of large dinos definitely declined with the loss of centrosaurines etc.



Note that the Hell Creek Fm is not the entire world, any
change in dinosaur diversity there may or may not reflect a change in global
dinosaur diversity.

Lockley et al report no decline in diversity in the late Maastrichtian of South America. But they don't know how closely the local record approaches the K-T boundary. Based on the egg record, Zhou suggested a rapid but gradual die off just before the end in the Nanxiong.




> > --this is true
> >whether or not some massive force hit. For example, what was it about the
> >dinosaurs that made them susceptible and not other living things?



And _I_ mean damn few other living things. Benthic foraminifera went through
pretty unscathed. Pretty much everything else of which we have fossils was
hit.

Crocodilians and other reptiles were virtually unaffected, even in NA.


Not everything equally severe... but remember that one surviving
population can be enough to let a species and thereby potentially a big clade
survive, so random comes in here.


Dalila Zaghbib-Turki, Narjess Karoui-Yaakoub, Rakia Said-Benzarti, Robert
Rocchia & Éric Robin: Révision de la limite Crétacé-Tertiaire de la coupe
d'Ellès (Tunisie): Proposition d'un nouveau parastratotype, Géobios 34 (1),
25 -- 37 (30 June 2001)

Apart from a shortened and slightly confusing abstract, this paper is in
French. Try to get a look at it in any case because the figures speak for
themselves.
Page 33 for example. The specific diversity of planktonic forams is almost
constant in the last 3 m of Cretaceous sediment; in the last centimeters it
rises a little, probably due to intensive collection. It surpasses the number
of 35 species at the K-T -- when it drops _straightly_ _at a right angle to
the time axis_ down to _one_ species.

Plankton extinction is well known to have been rather abrupt, but ammonite and other extinctions were gradual. Judd Case once presented evidence for gradual marine extinction in Antartica.




> Dinosaurs were supposedly more
> vulnerable because of their prodigious food requirements at a time of energy
> depletion.


By their size in general. Apart from food requirements it prevented them from
sheltering from ejecta, fire and acid rain,

Some dinos were small. Logically hypsilophodonts in remote regions like Australia should have been able to find shelter, or not have been more vulnerable than birds. If land crocodilians could survive in Gondwana why not some small dinos?



and it made them susceptible to
the impact itself, means, the corresponding humongous earthquake. It fits
neatly that all terrestrial (not semi- and aquatic) animals over about 25 kg
died out.
Any division between "winged" and "wingless" dinos is probably meaningless
here. The great diversity of flying theropods -- long tails, short tails,
alulae or not, teeth or not... --, not to mention that of secondarily
flightless ones, whichever these are, was cut down to a sad meager bunch of
Neornithes.


> The initial proliferation of ferns while the dust was settling rules out
> freezing temperatures and darkness. [...] Modern analogs
> of the K-T fern species, including a tree fern, require full sun to make
> spores, which are present in the upper impact layer.

Because there it says that the tree ferns formed the very last stage of the
fern spike.


But I was told they were already beginning to proliferate in the weeks while the dust was settling, which rules out freezing temperatures and darkness. (as does Kevin Pope's research indicating the amount of K-T dust was 2-3 orders of magnitude less than the amount needed to shut down photosynthesis.)



Nobody suggested that the ferns overgrew the world _while_ it was
dark and cold. The idea is that the ferns took over some months or maybe
years after the impact, when light and heat had come back

I'm sure you said once before there is no evidence for cold at the K-T.


(the latter
enhanced by the impact-induced greenhouse effect) and before angio- and
gymnosperms had reacted.

Just two weeks ago I've seen big fern meadows in the Alps (grass 10 -- 20 cm
high, ferns 50 -- 100), covering maybe several square km. Normal meadows like
the neighboring ones, except that almost all the visible vegetation consisted
of ferns. I don't know how they were caused, but they show that a fernland is
possible even in the presence of fast-growing angiosperms that didn't exist
at the K-T.


> Ordinarily the replacement of angiosperms and conifers with ferns would
> probably doom the dinosaurs since ferns aren't energetically rewarding.
> Tree ferns requiring full sun may well have been different.


Is there anything except insects that eats tree fern leaves

Some dinos included ferns in their diet, although it is questionable they were sufficient by themselves.

> In any event > recent research suggests only 10-20% of the biomass burned,

Isn't that equivalent to burning the leaves off _every tree_?!


More likely that forests were entirely burned down generally close, but survived in certain remote places.

> which implies widespread survival of "good" vegetation

Isn't the marine biomass, which obviously didn't burn, contained in the above
figure?

Lgically it should apply only to terrestrial biomas that could burn.

-----------------------------------------
So there is a little evidence that *Opisthocoelicaudia* and *Nemegtosaurus*
cooccurred. This makes it more probable that they were the same, but that was
it, IMHO it doesn't resolve anything.

OK, but AFAIK, all of the local sauropod postcrania is referrable to one genus.


Considering Jurassic and EK sites
around the world, is there anything strange about 2 species of sauropod in
the same place & time?


One difference between the Morrison and Nemegt is the presence of therizinosaurs-presumably high feeders-in the latter, which probably was at the expense of sauropod diversity.


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