[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

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

George Olshevsky (Dinogeorge@aol.com) wrote:

<Certainly there was a Bering bridge before the Santonian. That's why the
same >families< show up on both sides of it. But there was no land
connection during the Campanian,>

  Says who, George? The data supports faunal interchanges up into the
Camapanian, including sister taxa of select mammalian groups, so that just
one Turonian interchange is not likely the only one that ever occured.
Paleontological data in the area has shown that interchanges have occured
as either recurring landmass connections (Berringia) or as an ice sheet
(several Ice Ages and corresponding faunal interchanges with little gross
data of the ice sheet). If I were to apply the further data that only one
Senonian interchange were to have occured, then I must dismiss the
evidence of interchanges as an early, single ice-age event and find that
the shared Asiamerican Quaternary taxa, including mammoths, could only
have spread in once, whereas both archaeological and fossil data says
otherwise. It's not cladistic (which had nothing to do with
*Prenocephale*, by the way) analysis that supports this, but gross
morphology. But they must be wrong.

<a land connection that may have been restored only at the very end of the

  Based on...?

<In between those times, the regions were essentially isolated, and any
putatively "congeneric" species that occur there then are very likely
convergent or plesiomorphic rather than truly congeneric.>

  I'm not seeing any data, just supposition. What have you to say that
plesiomorphy outweighs synapomorphy or the occassional autapomorphies that
group these taxa together?

<If it was so easy to get across, why are there no ceratopine or 
centrosaurine ceratopians in Asia (for example)? Easy for one means easy
for all.> 

  Don't use this as an excuse. Asia lent its leptoceratopsids in the form
of *Montanoceratops* and *Leptoceratops*; the lack of identified
ceratopsids in Mongolia is not a problem, considering they may have been
selected against. Possible ceratopsid teeth have been found from the
Aptian--Albian and Turonian between Japan and Qazaqstan, which may have
been initial to their appearance in America. Absence of ceratopsids in
Asia after the Turonian, however, is not evidence against a land-faunal
interchange given the data in support of it for pachycephalosaurs,
tyrannosaurines, saurolophines, velociraptorines, several djadokhtatherian
mammals, *Catopsbataar*, carusioid lizards, caenagnathids, etc. In this,
the absence of ceratopsids is 1) either preservational, 2) they were not
capable of setting foot in Mongolian Asia, 3) or were not capable of
competing. This question has been raised by others considering the
biogeographic conditions, but as in other things, the data weighing in
suggests that the interchanges occured, were not a product of a single
interchange with several Campanian taxa sharing ancestry not present in
Coniancian, Santonian, or Turonian sediments, that many American taxa
arrived from Asia and may have gone back, and _vice versa_. I still don't
see what the problem is; it is an hypothesis, however, and the further
recovery of species on both sides of the Pacific are continuing to support
it, no matter how "strong" one things a set of apomorphies are, or are
weak (and the latter seems to be the bigger thing here, arguing against
sympatry because certain features are not considered "heavy" enough).

<By the way, Sullivan (pers. comm.) is reconsidering the North American 
Prenocephale species; he will be making new genera for them shortly.>

  Oh, good for him. I have a few choice comments to make on what he
considers a genus, based on the various tooth taxa, but hey ... one man's
genus and all that. But whatever Sullivan does, how does this mean to you?
Because someone creates a genus, suddenly its more real than the original
species allocation to another genus? Considering these skull caps are
crappy, I would be _very_ wary of their identification. Furthermore,
*Stegoceras* skulls (similar in morphology to *Tylocephale*) have varied
morphology with identical postcrania that supports the idea that the head
varied through life. I would not name the male and female forms of
*Monodon* different taxa because one supports a "super-tusk", a
differentiation I see in the work of Lucas, Sullivan, and Hunt. *Shanxia*
is, to agree with Sullivan, crap; but so is *Nodocephalosaurus*, based on
my own observation of variation in other "saichaniine" skulls. However, I
do look forward to his work.


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.

Do you Yahoo!?
U2 on LAUNCH - Exclusive greatest hits videos