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Re: Tyrant stuff (no longer ranting) (was RE: Rant (was RE: Details on SVP 20...



George Olshevsky (Dinogeorge@aol.com) wrote:

<About 13 years ago I, too, believed that rex and bataar were closely
related within Tyrannosauridae, but I never found a satisfactory answer to
the question of how bataar could have crossed the Bering Strait to give
rise to rex in North America (bataar is a bit earlier in time than rex).
Plus I actually got to see the bataar skull, and it is >so< different from
the skull of rex.>

  No argument there. I mean, a St. Bernard is also _so_ different from a
Chihuahua, too. Then there's the columbid *Didunculus*, the dodo. Nested
right inside all the rock doves, pigeons, and so forth. Extreme variation
can occur in any well-associated taxa, given circumstances. Both the
Hawai'ian i'iwi and huia are birds that have bills that have changed over
time, and within generations, so too have medium-sized ground finches from
the Galapagos. These differences occur to greatly differentiate mountains
and mole hills in the animal kingdom. Look at the Cape mole rat versus the
naked mole rat: both are, neotologically, considered the same genus, but
differ both horrendously, and greatly, but are nearly morphologically
identical, if not metabolically and dermally; the former, for one thing,
is coated in fine hair, the other nude. Semantics, on both sides of the
field, and I think one thing I am trying to get at here is to show how one
can say po-tay-to and the other po-tah-to, and both will be just as right
or wrong as the other. I can use your data against you, in other words,
which should say something for the argument.

<There aren't many genera described from both Mongolia and North America
(Saurolophus seems to be one, and it may simply have swum the strait 
somehow, although I doubt it), so it's necessary to examine the known
instance with a microscope to see whether there really is congenericity.>

  There have been several faunal interchanges during the Senonian of the
Cretaceous between North America and north-eastern Asia. That some taxa
appear earlier on one side and later, then in the middle on the other,
with some lineages on both, suggests that there was a double cross-over.
Asia may be the well-spring to tyrannosaurids, with *Alioramus*. But also
look at mammals and lizards, found throughout the Chinese and Mongolian
Gobi, that have been found in both Hell Creek and Judithian sediments. I
have heard of George's argument on how both species of *Saurolophus* are
"too different" to be the same "genus", and I wonder if this has some part
to do with the idea that the Berring Strait has "always been inundated
unless by ice".... For dinosaurs, at least, *Elmisaurus* (based on
morphological similarity, including several autapomorphies withing all of
Dinosauria), *Prenocephale* (on former *Stegoceras* crania, based on
morphological similarity), *Tyrannosaurus*/*Tarbosaurus* (same),
*Saurolophus* (and same) have all apparently crossed the bridge from one
side, to the other. *Albertosaurus*, some hadrosaur fragments, and some
ceratopsians have been found in northern Alaska at the critical Campanian
point where is it possible the Barun Goyot/Nemegt formations may have been
deposited with the similar Judith River Group. It is not unlikely to
suggest that eastern Siberia will yield these taxa as well in what may be
the Asiamerican Corridor.

<I think what really happened in Mongolia is that Tarbosaurus efremovi,
which may turn out to be a complex of species just like Albertosaurus is
in North America, gave rise to a giant Mongolian species, T. bataar, much
like Albertosaurus produced a giant North American species,Tyrannosaurus
rex.>

  Or, as has been suggested also, *Tarbosaurus efremovi* and
*Tyrannosaurus bataar* are the same species, as the former is based on a
subadult and the other on an adult sharing a complex of cranial features.
An ontogenetic (modern) assessment has not been done on this issue yet,
and hopefully Hurum and Carr will both be able to work on this. If not, it
needs be done and not use present taxonomy as an excuse to form
phylogenetic schema.

  Cheers,

=====
Jaime A. Headden

  Little steps are often the hardest to take.  We are too used to making leaps 
in the face of adversity, that a simple skip is so hard to do.  We should all 
learn to walk soft, walk small, see the world around us rather than zoom by it.

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