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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
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" <email@example.com>
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" <firstname.lastname@example.org>
(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!
Undergraduate Student, Carleton University
Vertebrate Paleontology & Paleoecology
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