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RE: Peering at review



--- "Williams, Tim" <TiJaWi@agron.iastate.edu> wrote:
>  
> I take your point.  However, in the case of "feathery dinos" there was no
> evidence either way; for the vast majority of theropods, no integument at
> all was preserved, making either interpretation (feathery or scaly
> integument) lacking in direct supporting evidence.  The "negative evidence"
> cut both ways in this case.  Typological preconceptions filled the vacuum,
> and therefore kept theropods featherless until the discovery of the Liaoning
> taxa.

Well-put.
 
> Hypothetical scenarios such as BCF fall into a different category.  True,
> the absence of Triassic arboreal basal dinosaurs with aerial capabilities
> does not *disprove* BCF.  However, the available evidence supports a
> contrary phylogenetic hypothesis: the origin of birds from derived theropod
> dinosaurs of the clade Maniraptora.  Thus BCF has two burdens to overcome:
> why existing phylogenies are incorrect, and why we should believe that there
> is a ghost lineage of tree-dwelling basal dinosaurs that gave rise to birds
> and terrestrial dinosaurian clades.

This is something many people seem to miss -- BCF does not necessarily disagree
with "standard" phylogenies. What it posits is that all the animals along the
lineage leading from basal _Dinosauria_ (or further?) to _Avialae_ (and beyond)
were arboreal/scansorial, and that many were flighted.

So, under BCF, you could have a standard phylogeny, but ornithischians,
herrerasaurids, sauropodomorphs, coelophysoids, ceratosaur[oid]s,
spinosauroids, carnosaurs, ornithomimosaurs, compsognathids, coelurids,
ornitholestids, enigmosaurs (oviraptorosaurs and therizinosaurs),
alvarezsaurids, dromaeosaurids, and troodontids (and probably some more clades)
would be secondarily terrestrial, all separately from each other.

The problem with BCF is that most of these clades do not show any sign of
descending from arboreal ancestors. A case could be made for the
deinonychosaurs (dromaeosaurids and troodontids), and wings seem to go back at
least to the enigmosaurs, but the basalmost known members of the other clades
do not, as far as I am aware, possess any arboreal or flight-related traits.
Nor do the basalmost known members of any clade including _Avialae_, with the
possible exception of _Eumaniraptora_.

=====
=====> T. Michael Keesey <keesey@bigfoot.com>
=====> The Dinosauricon <http://dinosauricon.com>
=====> BloodySteak <http://bloodysteak.com>
=====> Instant Messenger <Ric Blayze>
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