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Re: Polar Bear Challenge for AAH opponents
Dr C.J. Underwood (cju@liverpool.ac.uk)
Fri, 9 Dec 1994 11:30:08 GMT
Sir CPU (sircpu@aol.com) wrote:
: I would challenge the opponents of AAH could look at the skelaton of a
: polar bear and compare it to the skelaton of a black bear and identify
: which one is the "aquatic" animal.
For a skeleton out of context it would indeed be difficult to see which
of these two is semi-aquatic, but with fossil remains there is far more
can be done. Fossils of Polar bears would have a very different distribution
to those of blacks. As the majority would be expected to die either at
sea (or on ice) or during hibernation, their remains would be concentrated
in marine sediments (probably associated with signs of shark scavenging,
adherant shells on the bones etc) or shoreline breccias (the remains of
the seacliff screes they hibernate on) and beach sands. Only very rare
specimens of individuals which wandered inland (and are thus not aquatic)
would be found in fluvial settings.
Black bears would be found in largely inland settings such as braided river
systems and lacustrine deposits, as well as in caves where they died
during hibernation. Note that some of these carcases could rarely be
swept out to sea (as is the case with most of the dinosaurs known
from the British Jurassic which are from marine clays) and buried there.
Marine animals wil only under very exceptional circumstances get into
non-marine rocks. As the preservation potential of fossils in a marine3
environment is many times better than in a non-marine one, any fossils
found in fluvial sediments alone must be terrestrial or fresh water,
whilst something found in both is likely to be non-marine but coastal, and
something found only in marine sediments may still be marine or non-
marine (one example that comes to mind are the three skeletons of
the
terrestrial armoured dinosaur _Scelidosaurus_ known only fron deep marine
clays in England.
Even within fluvial settings, the same holds true, in that freshwater
animals are almost exclusively restricted to river channel and lake
sediments, whilst terrestrial ones can be found in both these (which
have a high preservation potential) and witin overbank floodplain
deposits. As an example, channel sands in the Cretaceous of the Isle
of Wight, England, contain fish, crocodiles, turtles and dinosaurs
(especially _Iguanadon_), whilst the overbank clays (which make up
most of the sequence) contain dinosaurs, very rare crocs and turtles and
almost no fish.(these are heavily etched scales which probably came
out of croc shit).
To get to your point, most homonid fossils are from overbank deposits,
and none are from marine sediments.
Charlie
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