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Re: Tyrannosaur numbers
It seems they were either selectively preserved (perhaps their risky
behavior put them at greater probability of getting buried rapidly), or
there were lots of them, or they had some characteristic that made
their bones more likely to survive long enough to be fossilized (tasted
bad, being just big, or something). Phil is correct in observing there
are lots of fossils from young T-rex (so they were successful breeders)
about the upper Cretaceous and quite a few random fossils from more
adult versions too at least in my little corner of Hell Creek. I
suspect that there are a good number of them in the ground yet to be
found. The number alive at anyone time and predator/prey ratios can
be deceptive though. For instance, a 10 foot thick layer of lake mud
could have been deposited over a really large amount of time and could
account for many, many generations of animals and literally thousands
of possible preservations in any particular location. If you have an
organism that has a higher likely hood of being preserved (for any
reason) it will definitely skew the ratio of preserved individual
compared to other less likely to be preserved organisms. You have to
remember the enormity of geologic time.
Certain types of preservational situations also will selectively
attract predators. One vegetarian prey animal gets stuck in the mud,
ten T-rex move in and all get stuck and there you are with a 10 to 1
observable preservational ratio. (Phil Currie is sure looking for that
situation again.) We may never know though because they are always
obscured in the ground but we only find the one on the edge of the
deposit and stop before the next specimen (one inch under the last
shovel scoop) . The obfuscations are many. There may be 10 more
animals buried along with Sue but if someone doesn't dig deeper there.
We will never know.
A building theory is (gaining followers) that T-rex were pack hunters.
Strength multiplied geometrically in numbers. There really might have
been a lot of them and there also may have been a lot more prey than is
indicated in the record.
I also don't think the general public understand the enormous amount of
work that it takes to get a huge animal like an adult T-rex out of hard
rock. I understand it took 30,000 hours to get Sue out of the ground
and prepped. (a few hours of legal work too!) The number of prepared
and displayed animals will always fall under the laws of supply and
demand. There are only so many institutions that will pay to get more
of the same out of the ground. A lot of researchers aren't interested
at all in more "common" dinos like Triceratops, T-Rex and certain
hadrosaurs. They wouldn't cross the street to dig one up let alone
spend funds to study them.
I think they are pretty common relatively. With that in mind, try to go
out and find one! Good luck.
On May 23, 2005, at 8:32 PM, Jordan Mallon wrote:
On 5/23/05, Phil Bigelow <firstname.lastname@example.org> wrote:
John Horner has an informed opinion on the number of _T. rexs_ that
existed at any one time, and from my limited experience as an
amateur, I think I'll agree with him. _T. rex_ appears to be quite
common in the Hell Creek Formation.
Despite my limited field experience, I can say with some confidence
that the same seems to be true in the Scollard of Alberta. I spent a
couple of days prospecting the Scollard Fm outcrops at Dry Island
Provincial Park last year, and it seems many (if not, most) of the
scattered remains my team and I came across were attributable to
Tyrannosaurus (surangular, longbone diaphysis, metatarsal, etc.). No
idea as to accurate species ratios, mind you, despite a microsite we
collected and analysed nearby.
B.Sc. (Honours), Carleton University
Vertebrate Palaeontology & Palaeoecology
Paleoart website: http://www.geocities.com/paleoportfolio/
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