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A new look for immediate sub-iridium layer bones...

    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
----- Original Message -----
Sent: Tuesday, May 14, 2002 10:43 AM
Subject: Re: K-T mammals

Andrew Farke wrote on 05/12/2002:

> In talking with Dean Pearson at the PTRM, the three-meter gap is shrinking
bit by bit, and it may just be a statistical effect. I'm not sure how valid
> this is or not, as I usually avoid the whole K/T problem.

Regarding the so called "three-meter gap". This gap shrinks if additional footprint data of dinosaurs is available. Footprints seems to be more acid resistent than fossil bones.

Martin Lockley described such a case for a site in southeastern Colorado in "Tracking Dinosaurs" (1991 page 202):

... the recent discovery of tracks right at the Cretaceous-Tertiary boundary,
only 37 centimeters, about one foot, below the famous iridium layer (Fig. 15.1).
This layer, caused by fallout from a major catastrophic event, perhaps impact
with a meteorite or a volcanic eruption, marks the end of the Mesozoic Era,
the end of the Age of Dinosaurs (1). For over a decade earth scientists have
argued about whether the dinosaurs died out gradually before the end of the era
or suddenly at the time of the purported catastrophe. Since there are no com-
plete or partial skeletons of dinosaurs in strata for at least three meters
below the iridium layer, paleontologists speak of a three-meter gap (2).

However, the discovery of tracks 37 centimeters below the iridium has narrowed
the gap to only one tenth of its previous magnitude. The tracks are indisputable
proof of live dinosaurs, in this case duckbills, living later in the Cretaceous than
was previously proven. A simple discovery of a few tracks (Fig. 15.2) improves
our resolution of dinosaur data at the Cretaceous-Tertiary boundary by an order
of magnitude (3).


1. Iridium, a rare platinum-group metal that occurs in extraordinary
abundance at the Cretaceous-Tertiary boundary, it is thought to be
related to an event that caused widespread extinction at this time.
Since tracks are evidence of live dinosaurs, documentation of
tracks either above or below the Cretaceous-Tertiary boundary provides
firm evidence of the activity of living animals.

2. There are many references to the "three-meter gap." David Raup
devotes a whole chapter to it in his book on the extinction debate.
Raup, D. M. 1986. The Nemesis Affair. New York: w. W. Norton, 220 pp.

3. The author discovered these tracks in 1989. A detailed report is
currently in preparation.


Heinz Peter Bredow