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rebbs, other stuff and (why not) SA ornithischians

I know Mati, but although Guille (Salinas) proposed
that Krito australis is more primitive than previously
though (as was also suggested by Jack Horner), I think
there other factors to consider.
It is pretty obvious that iguanodontians had an
important evolution in Gw (e.g. Muttaburra, Ouranoss),
and probably very basal hadrosaurs will be discovered
some day, but this is different. By the end of the
Campanian you have virtually hundreds of skeletons in
the Allen Fm and equivalents, as they are only in
northern hemisphere.
For me it is not out of mind that basal forms of North
American hadrosaurs, restricted there to marginal and
poor zones (i.e. they were succession first steps and
stayed later as relics in difficult regions) were the
brave guys adventured in the marshes and swamps that
led them to South America during Late Campanian. This
is my poor explanation of why those which migrated to
South American territories were not the super derived
forms (as Alamosaurus is not a saltasaurine, but a not
very derived form, probably relictual and restricted
to poor regions in South America). Perhaps all this
stuff could sound as ad hoc explanations (I described
it better in that work of the South American
Successional Structure that I've sent you, and the
other of Greater Gondwana faunas) but I think it is
reasonable. Nature could have done everything and we
just can imagine possibilities, but I agree with the
idea of Lehman that some primitive forms commonly stay
as relics in poorly-fossilizable regions (mountains,
ranges, and other). 

--- Matias Soto <soto@adinet.com.uy> escribió:

> > but up to now, hadros (and lambs) (IF THEY ARE)
> come
> > only from Late Campanian-Early Maastrichtian
> units,
> > which is consistent with the Bonaparte's
> biogeographic
> > proposal and the arrival of Gw taxa (IF THEY ARE)
> to
> > North America.
> But others (G. Salinas) found primitive characters
> in Late Campanian-Early
> Maastrichtian material (I mean, more primitive than
> contemporaneus North
> American hadrosaurs), suggesting that the arrival of
> hadrosaurs to South
> America was earlier than currently thought.
> Matías

Lic. Sebastian Apesteguia
Seccion Paleontologia de Vertebrados
Museo Argentino de Ciencias Naturales 'B. Rivadavia'
Buenos Aires, ARGENTINA

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