RE: Rugops: some questions

["Thomas R. Holtz, Jr." <tholtz@geol.umd.edu>]

> From: owner-dinosaur@usc.edu [mailto:owner-dinosaur@usc.edu]On Behalf Of
> Fabio Marco Dalla Vecchia
>
> I read the press releases regarding _Rugops_ and _Spinostropheus_.
> Unfortunately, the paper on the Proceedings of the Royal Society of London
> is not available to me and I need to clarify some points that appear
> unclear in the press releases.
>
> _Rugops_ is said to be 95 milion years old. So, is it Cenomanian?

Yes, it is from the Echkar Fm., Niger (Cenomanian).

> Which is the actual paleogeographic meaning of the discovery?
> South America
> and Africa were still in some connection during middle Cretaceous times as
> shown by fossils other than Abelisaurids.
> On the other side, Madagascar is supposed to have separated from Africa
> much earlier (Late Jurassic) and this would appear the main importance of
> the new finds. However, the press did not underline it.
>
> So, might you help me to understand the point?

Well, in my opinion this new data does not resolve the question of the order
of Gondwanan break up.

Several different hypotheses have been put forth with regards to which parts
of Gondwana divided first.  The "classic" model is an East/West split, with
South America/Africa vs. The Rest.  A newer model, based on the recognition
of the existence of abundant microplates, suggests that Africa separated
from the others first (i.e., that there was land connection between South
America, Antarctica-Australia, and Indomadagascar well after Africa had
separated).  Sereno et al. posit longterm narrow connections between the
various elements of Gondwana up until the end of the Early Cretaceous.

That might well be, but they evidence they use to support this is the lack
of a hierarchical structure within Abelisauroidea that matches any
particular break up pattern.  However, as discussed in a different thread
current on the list, our temporal and geographic coverage of the Mesozoic
terrestrial world isn't particularly good. Therefore, the lack of structure
may have as much to do with out lack of knowledge from large parts of the
appropriate regions and times than from the near-simultaneous breakup of
Gondwana.

Hope this helps,

                Thomas R. Holtz, Jr.
                Vertebrate Paleontologist
Department of Geology           Director, Earth, Life & Time Program
University of Maryland          College Park Scholars
                College Park, MD  20742
http://www.geol.umd.edu/~tholtz/tholtz.htm
http://www.geol.umd.edu/~jmerck/eltsite
Phone:  301-405-4084    Email:  tholtz@geol.umd.edu
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