[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]
Re: From Science New, and synonymous sauropods
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
> 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. 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
> > --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?
> You mean many 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. 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
Page 33 for example. The specific diversity of planktonic forams is
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. Within the next meter it rises to over
20 again and then stabilizes between about 15 and 20.
P. 29 shows the data used to plot this: the distribution of every
planktonic foram in the stratigraphy of the site. More than a third is found
the last time at the K-T boundary. A slightly smaller number dies out within
the next meter, which is when a similar number appears first. Only three
species die out within the last four meters of Cretaceous; only two new ones
appear in these layers (both survive far into the Paleocene).
P. 31 shows the temporal distribution of benthic forams from the same
First appearances cluster within the 2 m around the K-T, but not a single
extinction happens then. (That came at the Pal-Eocene boundary.)
All this probably says something about the event. What about a
ocean: the surface waters suddenly became acidic, then cold, then hot. That
should do a lot of plankton in but shouldn't harm the benthos.
The stratigraphy in Ellès is better resolved than that in the K-T
stratotype, El Kef. It might become the new stratotype.
> Dinosaurs were supposedly more
> vulnerable because of their prodigous food requirements at a time of energy
By their size in general. Apart from food requirements it prevented them from
sheltering from ejecta, fire and acid rain, 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
Any division between "winged" and "wingless" dinos is probably
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
> 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.
Have you, HP Tim Donovan, at last read the Science paper on the fern spike in
NZ? I sent you the pdf, didn't I? (If it hasn't reached you, please tell me.)
Because there it says that the tree ferns formed the very last stage of the
fern spike. 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 (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?
> In any event
> recent research suggests only 10-20% of the biomass burned,
Only? ONLY?!? Isn't that equivalent to burning the leaves off _every tree_?!?
> which implies widespread survival of "good" vegetation
Isn't the marine biomass, which obviously didn't burn, contained in the above
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. Considering Jurassic and EK sites
around the world, is there anything strange about 2 species of sauropod in
the same place & time?