Re: Gondwana Split May Complicate Mammalian Evolution

[João Simões Lopes Filho <jodan99@uol.com.br>]

I think it not necessarily complicate mammalian evolution, but make it
clearer. It seems a logical pattern. The problem is that science has allways
been very influenced by cultural concepts. Since most of paleontologists
came from Northern countries, mainly USA and Western Europe, these regions
was allways be considered as the center of evolution. Northern faunae are
ever been named as "advanced" and "superior", and Souther faunae as
"inferior" or "archaic". Modern discoveries are revealing a pattern that
will turn current points of view.

Can we assume a similar pattern for avian orders? A basal  "African" stock;
then a Neogondwanan stock; then a Northern stock?

Joao SL
Rio de Janeiro

----- Original Message -----
From: David Marjanovic <david.marjanovic@gmx.at>
To: The Dinosaur Mailing List <dinosaur@usc.edu>
Sent: Tuesday, January 22, 2002 7:36 PM
Subject: Gondwana Split May Complicate Mammalian Evolution


> > Wow!  If most modern mammalian groups are Gondwanan, and
> > most (or all) modern _birds_ are also Gondwanan (see article in
> > recent, one begins to wonder whether the Chixulab left much alive
> > in the Northern hemisphere at all.
>
> It's not that simple. The Afrotheria-rest split is put at 103 Ma ago by
> molecular clocks, which indeed happens to coincide very precisely with the
> Africa-SA split. The Xenarthra-Boreoeutheria split is put at 94 to 95 Ma
> ago... this predicts Boreoeutheria must have reached NA at that time via
> island-hopping or so. The Laurasiatheria-Euarchontoglires split lies
between
> 79 and 88 Ma ago.
>         Fossil evidence: A new study puts Zalambdalestidae and Glires
> together. Would fit this model. The same study supports (more weakly) the
> inclusion of Zhelestidae (paraphyletic or not) in Laurasiatheria. I cited
an
> SVP meeting abstract long ago which argues that Zhelestidae is related to
> Zalambdalestidae instead. Would be less evidence for, but still no
evidence
> against the model. Practically no Cretaceous mammals from Africa are
> known -- absence of evidence. :.-( Must have had a very interesting,
because
> isolated, fauna. Late Cretaceous SA, however, appears to be pretty well
> known. There we have an isolated fauna composed of AFAIK peculiar
> multituberculates, derived dryolestids, the enigmatic gondwanatheres and
> even docodonts, not to forget *Vincelestes*, a close relative of Theria,
but
> so far not a single therian sensu stricto (even though one metatherian
tooth
> has turned up in Madagascar and an astragalus of a eutherian, called
> *Deccanolestes*, is known from the end-Maastrichtian of India).
Dryolestids,
> gondwanatheres and the only known SA monotreme survived into the Paleocene
> when therians appeared, apparently quite suddenly, just as if immigrated
> from NA a very short time before the K-T.
>         Eutherians in Australia in the EK would add great support to the
> molecular scenario. Claims of such discoveries exist; *Ausktribosphenos*
and
> *Bishops* are often interpreted as such. At the moment it seems much more
> convincing to me that they, like monotremes and *Ambondro*, are members of
> Australosphenida, the basalmost branch of crown-group mammals. As I hear a
> JVP paper defending their eutherian status is in the works... let's wait
for
> it :-)
>         The paper cites a molecular clock date for the split between Meta-
> and Eutheria... at 173 to 176 Ma ago. I refuse to accept that. I hope the
> authors of that didn't accept Marsupionta. :->
>
> William J. Murphy, Eduardo Eizirik, Stephen J. O'Brien, Ole Madsen, Mark
> Scally, Christophe J. Douady, Emma Teeling, Oliver A. Ryder, Michael J.
> Stanhope, Wilfried W. de Jong, Mark S. Springer: Resolution of the Early
> Placental [ = crown-group eutherian] Mammal Radiation Using Bayesian
> Phylogenetics, Science 294, 2348 -- 2350 (14 December 2001)
>
> BTW, as I've said before, formal informal names like "boreoeutherians"
very,
> very strongly imply that there is a formal name Boreoeutheria somewhere.
> Let's simply forget Altungulata, like Pachydermata or Cotylosauria*! :-)
>
> * Which, unfortunately, has recently got a definition... it's a node-based
> clade which includes Diadectomorpha and Amniota. Why did they (Laurin &
> Reisz) have to bring that old discarded rhizome name back? :.-( (The
> PhyloCode dislikes such definitions, too.)
>