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Re: Statistics and the fossil record
At 11:21 PM 11/7/98 +0000, John V Jackson wrote:
[On the summary of historical geology]
>Thanks Jon, but I have taken all that into account.
Apparently you have not, at least not that I have seen.
>Do you mind if I take the liberty to repeat your first words here?:
Yes, but only because your quote appears to be more of a taunt than
a response to my point. I have yet to see you provide one shred of evidence
showing that your mode of argument accounts for the points I have raised.
>A lot of people are saying they're not sure if stats can be applied to
Hmmm... I don't believe I ever said that. Indeed, wait a few years
and I may publish some of my own work in that area. If you can't wait, check
out the _Dinosaur Systematics_ volume.
All I AM saying is that I don't think a statistical treatment of
phylogeny such as you are attempting is possible for Mesozoic terrestrial
vertebrates. Your sample size is too small, your sample is certainly NOT
representative of the population (the population being the entire diversity
of life through time and space), and your sampling method itself is nowhere
Maybe there is a non-parametric method which will suffice. Maybe a
gibbon will be elected the next governer of Minnesota. Stranger things have
>I would be more impressed if someone gave me an answer to the
>question of why so many small pterosaurs are found in the J and not the K,
>but pinnants (except Archae) are found in the K but not the J.
Actually, I liked Stan's point very much (indeed, I was about to
make it myself). The facies in which we find pterosaurs in the Jurassic and
the Cretaceous are somewhat different. If we have deposits similar to the
Niobrara Chalk in the Jurassic, and they show no large pterosaurs, then that
is one thing. However, it may be simply inequitable to compare a lagoonal
fauna with marine fauna. Remember point #8?
However, I should note that the explanation which seems to be
currently in favor is that birds presented greater competition for the small
marine flier niches in the Cretaceous, forcing pterosaurs to specialize as
large soarers. I'm not sure I buy that, but there it is.
>How much evidence vs. absence of evidence do we need?
As my biostratigraphy teacher would say, you only need one piece of
evidence to demonstrate the presence of a taxon. Negative evidence is,
however, still negative evidence, and ain't all that great. If you have no
reason to postulate the presence of a taxon, then you have no basis in
saying it was present. However, ghost lineages constitute a perfectly viable
reason to hypothesize a taxons presence. Then you can test away.
>They have found small olshevskyian bones in the Tendaguru,
And just what the boo-radley is an "olshevskyian bone?" For that
matter, why is "pinnant" necessary? Could we please stick to English
language? Most scientists (well, most responsible scientists) only make up
new jargon when it is necessary (often because the old jargon has been
co-opted). Let's try and stick with the jargon we have, so as not to confuse
the innocent bystanders.
>so some small arborial-type stuff was
>found there, but no larger "cursorial" maniraptorans. The ground there and
>in the Morrison has been scoured. Do you know how many turtles/crocs/small
>herbivores have been found in just those two formations?
This has been answered very effectively by Jerry Harris. Also,
please see points #1-#8 in my previous post. You may find some answers to
your questions there as well.
>They've found as much dinosuar material in the tertiary as they have pinnant
Discounting avian dinosaurs, this is still incorrect. Only reworked
non-avian dinosaur material has been found in the tertiary. Maniraptorform
(apparently = "pinnant") material has been recovered from before
_Archaeopterysx which does not appear to be reworked. Regardless of this, we
have *support*, in the form of ghost lineages, for the presence of
pre-archaey maniraptoforms. We have *no* support for post-Cretaceous
And before you start bellyacheing about the nature of evidence, let
me remind you that there are significant temporal gaps in the history of
many many taxa. The only difference between a gap between occurance data and
a gap between a first occurance and the beginning of a ghost lineage is the
degree of certainty concerning the length of the gap. I believe I may
confidently say that NO first occurrence in the fossil record constitutes
the *very first* occurrence of that taxon in the history of life. There are
*always* "ghost lineages" of some length. Always.
>"Oh - geology is too complicated, and you can't trust statistics, can you?
No one says geology is too complicated, nor am I saying that
statistics cannot be trusted. I am saying that you may be using a tool
*incorrectly*. What is the first thing you do with any statistical
proceedure? EVALUATE THE ASSUMPTIONS. When you can find a statistical
proceedure the assuptions of which will allow its application to the fossil
record in the manner you are attempting, do holler. I won't be holding my
>No, there may have been be dinos in the tertiary."
And so there may have been. When you have evidence, I'll be all too
happy to examine it. It'll only take one non-reworked Puercan tyrannosaur.
Jonathan R. Wagner, Dept. of Geosciences, TTU, Lubbock, TX 79409-1053
"Only those whose life is short can truly believe that love is forever"-Lorien