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Re: From Science New, and synonymous sauropods



Original Message by Tim Donovan Tuesday, 12. November 2002 12:56 

> >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.

Good point. So let's speculate a bit. The sudden absence of all big and 
medium-sized terrestrial herbivores should lead to denser forests. From what 
I've read, forests did become denser after the K-T boundary in western NA. 
This should have negatively affected species that needed more open forests or 
"open land". So maybe -- let's speculate another bit -- the death of the 
dinos was what did Djadochtatheria in, assuming a ground-squirrel-like 
lifestyle for these multituberculates that aren't known from any Paleocene 
sediments. Hard to test in the absence of a K-T boundary in Mongolia -- so we 
don't even know if they died out catastrophically in the first place -- and 
general ignorance of the climatic conditions -- today some savannahs are 
maintained by elephants that munch up every young tree, others are "real", 
they are too dry for trees... and comparing the Nemegt Fm environment, 
whatever it was, to a savannah may not be a good idea and so on.

Actually, the quote was more like "the answer to why the dinosaurs died out 
won't be found by studying dinosaurs", so the above lengthy diversion is my 
fault. :-]

> > > 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.

... which apparently happened in the mid-Maastrichtian. Then followed some Ma 
of stability, and then the K-T mass extinction. No?

>   Lockley et al report no decline in diversity in the late Maastrichtian of
> South America.

How big was their sample, how good is the stratigraphic resolution in that 
place... ref, please... hey, wait, _in_ the late Maastrichtian no decline is 
expected judging from the Hell Creek.

> Based on the egg record, Zhou suggested a rapid but
> gradual die off just before the end in the Nanxiong.

And as I wrote yesterday, Lucas suggests the opposite based on the same 
record, but stays cautious and prefers to wait for more fossils. Which is 
always a good idea :-)

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

I'm sure you've read Archibald's book from 1996, if only because it disagrees 
with the impact being alone to blame :-) -- it says that 30 % of lizard 
species didn't survive, but all "families" did; an example of how misleading 
ranks can be. Crocs... with the exception of *Brachychampsa* which apparently 
suffered from the drop in turtle numbers (I think this suggestion is also 
from that book... it's so long ago that I read it...), the semiaquatic and 
marine crocs of NA all survived according to my very limited knowledge, but I 
don't know if the dissolution of *Leidyosuchus* has changed this picture. 
Terrestrial LK crocs from NA aren't known. Elsewhere, however, it looks 
different... and K-T outcrops are largely absent. Of Ziphosuchia (see 
www.fmnh.helsinki.fi/users/haaramo/Metazoa/Deuterostoma/Chordata/Archosauria/Crocodylia/Crocodyliformes.htm
 
for what that is, or might be), only Sebecidae survived, maybe a bit more 
depending on the placement of *Bergisuchus* and *Iberosuchus* from the Eocene 
of Europe. No more Notosuchia, no more Baurusuchidae and so on. Asia had some 
very basal terrestrial crocodyliforms... none is known from the Cenozoic, 
though their LK record is AFAIK already very sparse. The description of 
*Calsoyasuchus* states that Goniopholididae is holophyletic after all, and it 
was gone by the Paleocene. So, even semiaquatic crocs, largely shielded from 
extremes in temperature and water chemistry, and independent of "green food 
chains", didn't sail through unscathed.
        Am I mistaken about Baurusuchidae? How old is *Cynodontosuchus*?

>    Plankton extinction is well known to have been rather abrupt, but
> ammonite and other extinctions were gradual.

Why do you present this as a fact? The few papers and mentionings in books 
I've seen on ammonite extinction contradict each other diametrically. There's 
one site in Spain where ammonites disappear gradually, and another one nearby 
where the same species stay all the way to the bitter, or rather acidic, 
end... if only I'd find the ref... it's not new, in any case. I assume there 
is new literature?

> Judd Case once presented
> evidence for gradual marine extinction in Antartica.

"Once". When? Archibald mentioned the same. I can't tell how much 
Signor-Lipps effect and reworking may be involved there; I don't expect 
intensive collecting in Antarctica, however.

>    Some dinos were small. Logically hypsilophodonts in remote regions like
> Australia should have been able to find shelter,

Why do you think Australia was remote when New Zealand wasn't, judging from 
the evidence of massive fire there?
        And of course we don't know if there were any ornithopods in LK 
Australia. 
Dinosaur bones from then are rare there...

> or not have been more vulnerable than birds.

Fine. Most birds died out. Even the relatives of *Ichthyornis* which should 
have been able to eat stranded carrion or suchlike didn't survive. No member 
of Enantiornithes, a diverse and globally widespread group in the 
Maastrichtian, is known from the Cenozoic...

>  If land crocodilians could survive in Gondwana why
> not some small dinos?

Most land crocs didn't survive. Those that did were predators and scavengers, 
and probably ectothermic enough to survive long periods of starvation.

> > > 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,

Obviously this isn't enough time for the entire succession described in the 
Science paper:

Vivi Vajda, J. Ian Raine, Christopher J. Hollis: Indication of Global 
Deforestation at the Cretaceous-Tertiary Boundary by New Zealand Fern Spike, 
Science 294, 1700 -- 1702

Just a few quotes...

"Recovery of New Zealand plant communities followed a pattern consistent with 
major climatic perturbations occurring after an impact winter that was 
possibly preceded by global wildfires."
        "The iridium anomaly of 71 [...] ppb [...] is the highest known from 
nonmarine rocks anywhere in the world [...]. The boundary location is 
consistent with the last appearances of Late Cretaceous pollen species 
(*Tricolpites lilliei* and *Nothofagidites kaitangata*) in the underlying 
sample."
        "The Late Cretaceous assemblages are diverse, with gymnosperms 
dominant, 
ferns abundant, and angiosperms common (mean values of 57, 25, and 14%, 
respectively). Gymnosperms increase to ~70% in the uppermost Cretaceous at 
the expense of ferns and angiosperms. The K-T boundary fern spike begins with 
an abrupt increase in ferns to 90% of the assemblage, mainly the form genus 
*Laevigatosporites*, but including the only common occurrence (8 %) of 
sphagnum moss (*Stereisporites*). Gymnosperms are greatly reduced, and 
angiosperms disappear completely. In searches of more than 2000 specimens per 
sample, no angiosperm pollen was observed over an interval of 12 cm from the 
base of the 40-cm-thick fern spike [yes, forty]. The fern spike is 
characterized by the successive dominance of different groups, such as ground 
ferns (*Laevigatosporites*, *Gleicheniidites*, and *Baculatisporites*) in the 
lower part [...] and tree ferns (*Cyathidites* and *Cibotiidites*) in the 
upper part. Modern relatives of these ground ferns are tolerant of open 
ground and acidic water-logged conditions, whereas modern tree ferns thrive 
in warm and humid conditions [...]. There follows in the Moody Creek Mine 
succession a marked decline in ferns and a rise in gymnosperms, principally 
*Phyllocladidites mawsonii*. This pollen type is related to that of the 
extant conifer *Lagarostrobus franklinii*, which inhabits the cool-temperate 
rainforests of Tasmania [...]. Angiosperms remain an insignificant component 
of the flora until 1.3 m above the K-T boundary. A short-lived recovery of 
ground ferns at the top of the fern spike may signal the first stage of 
regional climatic cooling, or it may be a localized phenomenon."
        "We recognize five phases in the floral succession: (i) abrupt 
extinction of 
local disappearance of terrestrial vegetation due to prolonged darkness, 
freeezing ground temperatures, possibly extensive wildfires, and acid rain 
[...]; (ii) colonization of a waterlogged, acidic, cool landscape by a 
succession of moss and ground ferns; (iii) expansion of tree ferns in the 
upper part of the fern spike at both Moody Creek Mine and mid-Waipara [...], 
indicating that a regional change to warm humid conditions followed earliest 
Paleocene cooling [the greenhouse effect from CO2 from fires and dolomite and 
the methane from clathrates?]; (iv) decline in tree ferns before a long-term 
rise in cool-temperate gymnosperms, consistent with evidence in the marine 
record for climatic cooling in the early Paleocene [...] [after the 
greenhouse effect, in the absence of big animals, the dense forests sucked up 
even more CO2 than had led to the greenhouse effect, leading to cooler 
temperatures?]; and (v) recovery of angiosperms to near Cretaceous levels, 
possibly related to a warming climate in the late early Paleocene [the return 
of some sort of normality?]."
        "I[t] has also been argued, based on the abundance of sootlike carbon 
and 
oher inferred combustion products [...], that the bolide impact ignited 
extensive forest fires. It was initially suggested [...] that the fires would 
have been mainly restricted to North America, but subsequent models have 
indicated that thermal radiation generated by the ballistic reentry of ejecta 
may have led to spontaneous outbreaks of wildfires worldwide [...]. The 
presence of fullerenes in New Zealand K-T boundary clays [...] supports the 
theory of the occurrence of local wildfires. However, although wildfires may 
explain the widespread devastation of forests, they [alone!] do not explain 
the succession observed in the New Zealand palynological record or the 
prolonged delay in recovery of Cretaceous-type floras."

> (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.)

This research indicates that the very same darkness began _a few hours 
later_, that soot instead of dust was the main culprit, and it says nothing 
about the nitrogen dioxide (a dark, intransparent, beautifully red-brown gas) 
that the impact must have produced in large amounts. As I wrote in 
altperdino@yahoogroups.com maybe three times.

> >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.

I certainly wrote that, and I also wrote, several times, that an impact 
winter should be far too short [months] to be recorded in a sediment!!! (If 
we don't find lake varves.)
        Some confusion probably arose because there apparently was a colder 
episode 
after the initial greenhouse effect. Another quote from the same paper: "The 
fern spike [...] extends into the upper part of the earliest Paleocene [...] 
foraminiferal zone (P0) in the mid-Waipara and Hokkaido marine sections 
[...], implying a duration of ~30,000 years. Radiolarian biostratigraphy 
[...] indicates that the interval of gymnosperm dominance may have lasted for 
1 million years. These time frames are far greater than the predicted 
duration of months to hundreds of years for climatic changes directly 
associated with an impact event, such as impact winter and greenhouse warming 
[...] [probably not consistent with my speculation above that the tree fern 
time represents the greenhouse effect]. The New Zealand vegetation record 
supports evidence from the local marine record [...] and South Atlantic deep 
sea cores [...] that the K-T boundary impact, through mass extinction of 
oceanic plankton and mass injection of CO2 into the atmosphere, caused major 
disruption of the carbon cycle, which resulted in pronounced climatic 
oscillations for at least 1 million years of the early Cenozoic."

> > > 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.

Very unlikely, see above, because much of the ejecta must have left the 
atmosphere and reentered all over the planet.

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

I've never seen this explicitely. (And except in your posts, I always saw 10 
% when any figure was given.)

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

So far. :-)

> >[...] 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.

Good argument. However, apart from *Therizinosaurus* itself there weren't any 
really high therizinosaurs as far as is known.

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