In 1998 Zhao produced a paper
about "excitations" and iridium
anomalies in dinosaur eggshells of
putative K-T age. His purpose was not to
corroborate the impact
scenario, as he had already attributed extinction to
dessication, trace
mineral concentration and poisoning.
Which
could in principle explain why that area wasn't repopulated within the same
millennium. Nothing else. BTW, poisonous trace materials like arsenic are often
accumulated during or after fossilisation. Bones from the Morrison Formation
contain so much uranium that one can prospect for fossils with a Geiger counter,
and some bones have even been ground by criminals to get at the
uranium!!!
Zhao's
principal
motivation was to strengthen the case for continuous deposition
during the
K-T interval in the Nanxiong basin. Most researchers,
e.g. Russell, maintain
that the Nanxiong (or Pingling) - Shanghu contact
is disconformable, an
opinion apparently based at least partly on the lack
of an iridium anomaly
there. By 1993 Zhao was virtually alone in
arguing for continuous
deposition. All of his geochemical results
are questionable. So much for
poisoning, "excitations" and a
conformable contact. With regard to the
latter, however, the hiatus
may be brief, inasmuch as chron 29R seems extant,
above and below the
boundary.
The boundary itself, however, lies in a short
normal subchron... (that was used to show continuous deposition in, IIRC,
Montana).
The Nanxiong
may shed light on dinosaur extinction. The evidence is
not
consistent with sudden death by impact. The egg type
Nanshiungoolithus
disappears at a lower stratigraphic level than
Stromatoolithus,
Shixingoolithus and Ovaloolithus, which
vanish at a lower level than
Macroolithus. The latter alone
persists to the top of the Nanxiong, which is
apparently not quite the end
of the Cretaceous.
What if I suggest the Signor-Lipps effect for
that? Is that plausible?
The egg record in China, as
in Europe, does
not support sudden, catastrophic extinction of all or most
taxa at the
very end.
AFAIK, the K-T boundary is not preserved in ANY
continental European sediment, so probably the European egg record supports
NOTHING. The red Maastrichtian sediment -- well, sample size = _one_ --
I've seen in Aix-en-Provence (contains sauropod nests) simply stops and grades
into a grey GALLO-ROMAN sediment that contains ceramic fragments and pig jaws
B-) ...
Does it
support a specific alternative? It is interesting that
Mikhailov
suggested the Macroolithus egg type was laid by T. bataar,
inasmuch
as it is the largest of the elongatoolithid eggs of presumed
theropod
affinities, and abundant, like T. bataar, in the Nemegt
svita e.g. at Tsagan
Khushu.
[...]
The Nanxiong
record may be relevant to global extinction in that it
demonstrates
Tyrannosaurus radiated into paleoenvironments where it did not
belong c. 65 Ma, with devastating results.
[...]
How could
Tyrannosaurus have outlasted its dinosaur quarry long enough
to
account for the higher occurrences of
Macroolithus?
Macroolithus indeed belongs to
Elongatoolithidae, and this to the ornithoid shell type. Oviraptorid embryos
have been found in elongatoolithid eggs. A Troodon nest, however,
contains dinosauroid-prismatic eggs, which I regard as evidence that the former
is closer to birds (whose eggs, ô surprise, all belong to the ornithoid eggshell
type) than the latter. If Macroolithus was laid by a
tyrannosaur, then tyrannosaurs are closer to birds +
oviraptorosaurs than troodontids -- I can't remember anyone right now who
has ever thought this.
AFAIK, the only reason ever to
ally Tarbosaurus with Macroolithus is that both are big and
more or less of the same age and place.
So perhaps Tyrannosaurus gradually
annihilated and outlasted the
Nanxiong herbivores, just as it may have
done to earlier Nemegtian taxa
So you know of a place where the Nemegt Formation
continues to the K-T boundary, and its upper part is devoid of herbivorous
dinosaurs? I'd be delighted to read of such a place... though judging from what
little I know about LK Mongolian sedimentology, such a place doesn't exist.
Perhaps :-> someone else knows?
and, to a lesser extent, to the
mid-Maastrichtian fauna of America.
What about the end-Maastrichtian fauna?
Etc.
...?
[...]
Although
teeth from
the upper Nanxiong indicate the presence of a tyrannosaur as
big as T. rex,
the contemporary Nanshiungosaurus was only 6m
long. That was far smaller
than Therizinosaurus, which faced
T. bataar, a smaller hunter than T. rex.
Nanshiungosaurus was even smaller than Segnosaurus, which
confronted the
diminutive Alectrosaurus. In no other Asian
environment was there such a
mismatch.
The biggest tiger is in Siberia. Elephants and
buffaloes are in Africa. What is endangered is not the Siberian Tiger's prey,
but the tiger subspecies itself...
Tyrannosaurus seems to have been an
intruder in south China, where the
local endemics were not co-adapted and
soon succumbed.
[...] and south China may have been isolated for
most of the intervening 12
m.y. (the presence of the primitive
Alioramus in the Nemegt svita at Nogoon
Tsav suggests gradually
increasing contact between formerly isolated regions
of
Asia.)
Isolated? How? Why?
[...] Microhadrosaurus may have been
equally challenged. Sometimes compared to
Edmontosaurus, it
might have been the archaic Tanius,
Does this mean Microhadrosaurus -- 2,4 m
in length -- is a juvenile (no big surprise, but I haven't read this anywhere so
far...)?
Perhaps
one or more
other taxa nested elsewhere, and the predator subsisted to an
extent on
pterosaur nests, turtles, etc., for a time,
Just for size comparison -- imagine cats
subsisting on INSECT EGGS... This example may be wrong by an order of magnitude
or more, but that's still close enough.
accounting for various other
extinctions,
Turtles didn't go through unscathed, but they did
survive quite well, and most AFAIK were small freshwater inhabitants... I
absolutely can't imagine tyrannosaurs surviving on such turtles for thousands of
years.
although such a doomed, marginal
existence
should lead to doom very, very fast because
population sizes must have plummeted below anything sustainable -- or it
should lead to EMIGRATION even faster.
But even before that, it should lead to
immigration of herbivores from somewhere else!
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