Re: Gliders to Fliers?

[Josh Smith <smithjb@sas.upenn.edu>]

Matthew Bonnan wrote:

> Josh Smith said:
> >This is NOT to support George's arboreal theropod ideas, but where the
> >hell is the evidence that all of the early ceratosaurs were living in
> >hyper arid environments with no trees??????
> >
> >Petrified Forest Member of the Chinle Formation?  There is evidence of
> >abundant and widespread plant life all over in these rocks. LARGE trees.
> >
> >Red Beds DO NOT necessarily indicate hyper aridity and these theropods
> >are not being recovered from the aeolian deposits.  True, we do find
> >coelophysoidish teeth in cross-bedded aeolian sands in the Bay of Fundy,
> >but they were not exclusively there.
>
> What is the Cactus park environ like, where Dilopho-sized tracks and smaller
> are found?  I was under the impression that during the Trias and early
> Juras, with the landlocked continents of Pangea the inner portions of the
> continents became very arid and dry.  Is there any evidence that the
> Petrified Forest was a large oasis of sorts?  I've read some Frakes and Judy
> Parrish things on climate: any new interps of Trias climate: less dry, more
> wet, what?
>
>

    The common interpretation of Late Triassic and Early Cretaceous
environments were very dry because of the geography of Pangea is certainly
correct, in a broad sense.  However, we are not talking about a universally
"very arid" time.  The widespread occurrences of mottled mudstones that can be
interpreted as pedogenically altered fluvial overbank fines suggest significant
biogenic activity from plants and soil microorganisms. Significant soil
formation is not indicative of hyper aridity.  What I have seen in the Sahara,
Saudi Arabia, and the driest parts of North America is an almost conspicuous
lack of any significant pedogenesis for the most part.  Granted those areas
where Triassic caliche horizons are preserved are indicative of pretty dry
circumstances, but not all of the pedogenic carbonates preserved in the North
American Triassic were caliche.  And there are significant floras known from
much of the North American Triassic and Early Jurassic (the aeolian sands
notwithstanding, of course, but then the aeolian sands are not the most common
footprint producers and I don't recall any ceratosaurids that have been found
in aeolian deposits).  You do not get large bodied macrofloras in hyper arid
environments for the most part.  I am NOT saying that the environments we are
talking about were not dry.  I am NOT advocating boreal swamps here.  However,
when we talk about "hyper aridity," we are discussing Sahara levels of rainfall
and no major macroflora.  I do not the think that the available data are
indicating "hyper aridity" for the majority of environments where early
ceratosaurs have been recovered on this continent.  Red beds are not
necessarily indicative of hyper aridity, though they do seem to represent dry
areas for the MOST part.  However, it is more complicated than just being able
to use them as a blanket statement.

Does that help, or make it more confusing?

--
Josh Smith
Department of Earth and Environmental Science
University of Pennsylvania
471 Hayden Hall
240 South 33rd Street
Philadelphia, PA  19104-6316
(215) 898-5630 (Office)
(215) 898-0964 (FAX)