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Re: extinction in China (quite long)



     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!