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I thought I had sent this message earlier,
but it hasn't showed up on list, so my apology if the earlier transmission now
shows up, in addition to this:
Heinz Peter Bredow said, "Regarding the so
called "three-meter gap" [beneath the K/T iridium layer]. This gap shrinks if
additional footprint data of dinosaurs is available. Footprints seems to be more
acid resistant than fossil bones....Martin Lockley described such a case for a
site in southeastern Colorado in "Tracking [Dinosaurs, 1991, page 202]".
That brings to mind an interesting
consideration: In the instance Lockley describes, the ornithopod
footprints were only 37 cm below the iridium layer, and, as we know, to date, no
dinosaur bones have been found equally near the K/T (iridium) layer. It is
HPB's statement that, "Footprints seems to be more acid resistant than fossil
bones", that really 'hits home' with me.
Why? Other than Early Cretaceous
natural casts of bones that have disintegrated, most all of the bones and teeth
found in this area of Maryland are those preserved in the very protective (from
acid ground waters in this quite swampy area) Arundel
clay.
That makes me wonder if the paucity of
dinosaurian (and other) bones immediately beneath the K/T iridium layer might
be, in large part, due to the intensely acid rain that would undoubtedly have
resulted from the impact event, soaking down into bone-bearing layers and
dissolving such materials.
Point of this story? Aside from watching for footprints, I suggest paleontologists keep
a more careful outlook for natural casts of dinosaur
(and other) bones (and teeth) within reasonable distances below the iridium
layer. Natural casts of bones and teeth are
much more difficult to notice and identify than are silicified natural bones and
teeth, and they may be the only evidence that is left of these items in many
immediately sub-K/T areas. If such casts are there, finding
them could shed considerable light on immediately pre-impact vertebrate
diversity, etc.
Ray Stanford
"You know my method. It is founded upon the observance
of trifles." -- Sherlock Holmes in The Boscombe Valley
Mystery
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