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Re: cretaceous landscapes ; Long but worth it!



I forgot who had asked for this so I apologise to anyone who may feel this is
a waste of their bandwidth.

A few  comments from a small sliver of the Early Cretaceous...

 The Cretaceous  Period was the longest period of the Mesozoic. Based on DNAG
Geologic Time Scale (1983) the Cretaceous Period lasted for 80 million years
give or take a couple million years. It was during this  Period that
angiosperms first arose and diversified. So depending on what age/stage one
is interested in would determine the type of flora one would expect to see.
 Therefore, it would be difficult to describe a typical Cretaceous
landscape.For starters, what type of environment are you trying to
reconstruct? What fauna do you wish to include? As an example, I am working
in the Early Cretaceous Arundel Formation which is generally believed to be
Aptian age (119-113 Ma) after which saw the rise of flowering plants in the
Albian.  According to Brenner (1963),  based on pollen and spore studies,
 the Arundel flora was dominated by gymnosperms and other conifers  ( 60%)
and ferns (30%) and bryophytes (1%). Moreover, Brenner likened the _climate_
and _paleoecology_ of the Arundel to that of the warm and moist  broadleaf
evergreen forests of New Zealand and Australia. Glaser's  (1969) publication
on the petrology of the Potomac sediments interprets the sediments to have
been laid down in terrestrial-fluvatile conditions, possibly braided stream
complexes close to shore and compared it's depositional character to that of
the Mississippi delta (a fairly warm moist environment as well). The
"typical" flora consisted of the genera; Podocarpacea, Araucariaceae  (like
the Norfolk Island Pine), Taxacea, Cupressaceae, and Pinaceae  (Pines). There
were also Clossopolis, Brachyphyllum, Pagiophyllum and a "taxodioid conifer"
( Hickey, personal communication) that was once though to be a type of
Sequoia. Other well known but little represented flora are the Magnolias,
Gingkos, Cycads  and Equsites (horsetails). Many of the above genera have
living descendants or at least appear to  have modern day counterparts. Of
the dinosaur and other fauna known from the Arundel,  all major clades were
represented. Sauropods by Astrodon spp., Theropods by "Dryptosaurus" (
Allosaurus sp.) and "Coelurus", Ornithomimids by Archaeornithomimis and
Ornithomimus sp., the Ornithician Priconodon crassus and possibly the
ornithopod Tenontosaurus. There were crocodiles (Goniophololids), turtles,
mollusks (Unio) , and even a Hybodont shark in the streams.  The Wealden Beds
of England  may be a comparable European analog.
The transition from Arundel to the overlying Potapsoco-Raritan Formation  saw
the advent of the Albian Stage of the Late Cretaceous and the first flowering
plants. 

The point of this being that there was no "typical Cretaceous landscape"  but
there may have been  typical landscapes for each geologic stage depending on
the paleoecology that was operable at the time. So a generalized Aptian
landscape of the eat coast of the USA (Maryland) might be drawn with abunant
conifers as the major forest canopy,  then with Magnolids, Cycads,  and ferns
as the undergrowth and stream bank inhabitants. The terrain woild be
relatively flat with slow meandering streams that have a few cut off meanders
and with the exception of the dinosaurs and other extinct animals, it would
look remarkably similar to many modern environments. And  _no_ volcanoes!

References:
Brenner, G. J., 1963 , The Spores and Pollen of the Potomac Group of
Maryland. Bulletin 27, State of Maryland Dept. of Geology, Mines and Water
Resources (Now called The Maryland Geologic Survey). 215pp

Glaser, J. D., 1969, Petrology and Origin of Potomac and Magothy (Cretaceous)
Sediments, Middle Atlantic Coastal Plain. R.I no. 11, Maryland Geologic
Survey 101 pp.

Kranz, P.  M., 1989, Dinosaurs in Maryland, Educational Series no.6 ,
Maryland Geologic Survey.******
*Note: This last reference hs a couple of excellent drawings by Greg Paul, a
member of this list and fellow Baltimorean. Any fans of Paul might want to
add this to their collection.

Regards,
Thomas R. Lipka
Paleontological Studies