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Re: Feathers on Bloody Everything

At 02:04 PM 10/6/98 -0400, Ronald I. Orenstein wrote:
>In the midst of all the (premature?) excitement, folks, let's not forget
>that there is pretty good evidence, in the form of integumentary casts and
>similar fossils, that at least some adult dinosaurs did NOT have feathers -
>including theropods like Carnotaurus.  Even if the new Therizinosaur is
>decked out like a peacock, the most you could say is that feathers are
>likely to be shared derived characters only for descendants of the common
>ancestor of therizinosaurs and birds

Okay, to be fair, the best we can say is that the most recent common
ancestor of the new therizinosaur, _Caudipteryx_, _Protarchaeopteryx_, and
birds was feathered (given that the avian nature of _Caudi_ and _Protarchie_
is not firmly established).  On top of that, we (so far) just have people's
word that the new therizinosaur IS a therizinosaur.  Okay, so the folks
describing it DO know a therizinosaur when they see it, but until such time
as it is illustrated, we must consider it just a rumor.

>- and. like mammalian hairs, can be
>subject to secondary loss.  There is nothing parsimonious about assuming
>from what we know now that, say, Triceratops had feathers (good grief, what
>a thought!) - especially if you consider, not just the feather evidence,
>but the whole evidence on dinosaur integument.


As Josh pointed out, we can (and do, often over beers) come up with various
scenarios to explain the distribution of soft tissue features or behaviors
in various extinct lineages, but there is a difference between a scenario
and the evidence (if any) to back it up.  Personally, I like the ideas that
many groups of theropods (at least) as being downy as hatchlings, that
endothermy was a juvenile trait found widely distributed in dinosaurs, and
that birds retained and elaborated these juvenile features (and small body
size) into adulthood.  However, just because I *like* the idea doesn't mean
it is the best currently supported by the data.

We can be relatively certain that the most recent common ancestor of all
modern birds was endothermic, but as we move beyond that we move into the
realm of speculation and extrapolation from what evidence is there.
Similarly, as we move from the most recent common ancestor of known
feathered forms outward we move into much less secure realms concerning dino
integument (particularly as our next secure step on that path is way down at
_Carnotaurus_, leaving our knowledge of non-maniraptoriform tetanurine
integument unclear at present).

Oh, and another SVP tidbit: Dan Chure pretty securely trashed the the
_Allosaurus_ status of the Australian "_Allosaurus_".  It's a tetanurine,
and maybe even an allosauroid carnosaur (maybe), but it lacks any features
to securely unite it with the North American genus _Allosaurus_.  Thus, this
one supposed "survivor" of Jurassic forms into the mid-Cretaceous of
Australia is no more.

However, in its place, _Minmi_ is coming out in phylogenetic analyses as a
basal ankylosaurian, preserving some conditions prior to the
Nodosauridae-Ankylosauridae split.  Thus, in a sense, it is a survivor of
Middle Jurassic "grade" into the mid-Cretaceous.

More later.

Thomas R. Holtz, Jr.
Vertebrate Paleontologist     Webpage: http://www.geol.umd.edu
Dept. of Geology              Email:tholtz@geol.umd.edu
University of Maryland        Phone:301-405-4084
College Park, MD  20742       Fax:  301-314-9661