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RE: phyletic bracketing
From: "Ken Carpenter" <Kcarpenter@dmns.org>
For example, because guarding of nests occurs in crocs and in most birds,
then nest guarding must >have occurred in dinosaurs (this is a general
statement to illustrate how PBA works to those who >are not familiar with
it).
Is that what PBA says? I'm with David on this one. PBA says that (this is
key) >>>lacking evidence to the contrary<<<, it is most >parsimonious< to
assume that nest guarding was common to dinosaurs. I trust Dr. Carpenter
phrased himself this way, though, so as to stir the pot, as he put it. ;)
The problem of PBA is that it cannot explain novel structures, and indeed
in the strict adherence >to the techniques does not allow for such
structures (fireworks at this point, I am sure). I offer as >examples: the
predentary bone of all ornithischians, the rostral bone of all
ceratopsians, etc. >Neither of which occur in either birds or crocs.
I don't see a reason by PBA needs to explain novel structures to begin with.
PBA concerns itself with structures that must be inferred (i.e. are thus
far missing from the fossil record); not structures that we know with
certainty were present. It's a sort of default setting that can be vetoed
in light of contradictory evidence.
From: "David Marjanovic" <david.marjanovic@gmx.at>
I just wonder why you suddenly try to begin a discussion on this, seemingly
not in response to >anything I've seen onlist recently...
Who cares?!? It makes for interesting chit-chat. Especially in light of
the lull we went through earlier on this list.
From: "Tim Williams" <twilliams_alpha@hotmail.com>
(I am aware that skin impressions are known for _Carnotaurus_ and
_Tyrannosaurus_, and both >show a rather leathery and tubercular texture.
However, I don't believe this automatically >*disproves* the existence of
pre-maniraptoriform feathers. Juveniles may have been feathered, >and/or
feathers may have been limited to the extremities in adults.
Keep in mind the scaly allosaur hatchlings reported at SVP this past year!
Jordan Mallon
Undergraduate Student, Carleton University
Vertebrate Paleontology & Paleoecology
Paleoart website: http://www.geocities.com/paleoportfolio/
http://dino.lm.com/artists/display.php?name=Mallon
MSN Messenger: j_mallon@hotmail.com
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