Re: Non-theropod dinosaurs and feathery/fluffy integument

[dinoboygraphics@aol.com]

Just to ease doubt with an additional personal observation... I got to 
see the quilled psittacosaur specimen 2 months ago when I was in 
Germany, and the "quills" do indeed exhibit a placement relative tot he 
neural spines that appears too regular to be plants or anything else 
haphazardly "washed in".  That said, I would also like to see a more 
indepth analysis of the geochemistry and morphology of the structures.

To answer Brandon's question; it seems to me that the liklihood of some 
sort of "dinofuzz" being primitive to non-coelurosaurs depends on how 
closely related pterosaurs are to dinosaurs.  If there is a close 
relationship, you can make a reasonable inference that dino/ptero fuzz 
arose prior to the origin of dinosauria (although it still may have 
evolved separately even if a close relationship is found).  If 
pterosaurs are only distantly related to dinosaurs, then you have no 
phylogenetic support beyone the coelurosaur fossils that have 
insulatory pellage, and that makes a much weaker argument for extending 
insulation to even the base of theropoda, let alone to other dinosaur 
clades.  And the scales preserved in Psittacosaurus (the 
"quill-specimen" definitely has scales preserved on the rest of the 
body) argues against some sort of insulatory covering in this group.

Considering the association of scales in Juravenator is similar to that 
inferred for a small patch in Scansoriopteryx (which clearly had at 
least dinofuzz, if not true feathers), it doesn't seem like much of a 
challenge to other portions of the body having insulatory structures, 
but that only takes you to the base of compsognathids (if it's even a 
natural group).  Beyond that it's speculation; that doesn't mean it's 
wrong (hopefully additional fossils will show us one way or another) of 
course, but it is without much evidentiary support at this point.


Scott Hartman
Science Director
Wyoming Dinosaur Center
110 Carter Ranch Rd.
Thermopolis, WY 82443
(800) 455-3466 ext. 230
Cell: (307) 921-8333

www.skeletaldrawing.com


-----Original Message-----
From: Jura <pristichampsus@yahoo.com>
To: dinosaur@usc.edu
Sent: Fri, 15 Jun 2007 2:39 am
Subject: Re: Non-theropod dinosaurs and feathery/fluffy integument



--- Brandon Pilcher <trex_kid@hotmail.com> wrote:

> Why is it conventional for paleoartists to cover
> their smaller theropods (or
> infants of larger theropod genera) with feathers or
> proto-feathers, but not
> dinosaurs from other clades? I have almost never
> seen, say, a "coated"
> ornithopod, psittacosaurid, or stegosaurid
> hatchling.

+++++++++++++++++++++++++++++++++

I'm not sure just how conventional sticking feathers
on dinosaurs has become. It's popular among many dino
artists on the list, but there are still a fair amount
of dino books out there with scaly "raptors" adorning
their pages (admittedly, these are not the best books
on dinosaurs).

As for why you only see them in theropods, the answer
is simple. Theropods (maniraptors/coelurosaurs in
particular) are the only clade to show their
development. Phylogenetically, it seems most
parsimonious to assume that feathers evolved somewhere
in Coelurosauria.

This means that all dinosaurs outside this clade
(which are, in fact, most dinosaurs) would still be
scaly. This has been supported by the numerous skin
impressions from Carnotaurines, Sauropods, Ceratopians
and Hadrosaurs; all of which show scales.

The only possible exception is a single
_Psittacosaurus_ specimen announced in 2002. The
specimen appears to contain some type of filamentous
structure on the proximal part of the tail. It's
relation to feathers is considered nonexistent (it
shows absolutely zero feather/protofeather
morphology).  They were probably modified scales (as
suggested by their proximity to true scales - a
problem for feathers ), or something completely
unrelated to the specimen. The paper states that one
can discount these being plant remains, but gives no
actual reason why (just states a personal
communication).

Personally I'm leery on this specimen. The only data
on this beast comes from a short decription in
Naturwissenschaften. Until I see a more thorough
analysis of the "filaments," I'm going to retain my
skepticism.

__________________________________________


As much as I miss the
> featherless, scaly dinosaurs of my childhood's 90s
> dinosaur books (in my
> opinion they look much sleeker, shinier, and more
> lithe than the dinobirds
> of contemporary reconstructions), I believe all of
> the smaller dinosaurs (as
> well as the young of the larger kinds) probably had
> integumentary covering,
> for purposes of insulation.

+++++++++++++++++++++++++++++++++++++++

All dinosaurs had integumentary covering. Scales ARE a
type of integument. As for filamentous integument,
that is probably restricted to coelurosaurs only
(probably closer to Maniraptora too).

________________________________________

> All smaller endotherms need insulation.

++++++++++++++++++++++++++++++++++++++++

This statement requires the assumption that all
dinosaurs were endotherms. Despite the sway of popular
opinion, the evidence is strongly ambiguous on this
matter.

_____________________________________

> BTW, is it possible that some dinosaurs may have had
> "nappy" or kinky
> integument (thinking Afro-type), as opposed to the
> straight fluff/feathers
> usually found on fossils bearing impressions?

+++++++++++++++++++++++++++++++++++++++

I don't see why not. I'd have to wonder what
environmental forces were pushing for nappy hair
though.

Jason

"I am impressed by the fact that we know less about many modern 
[reptile] types
than we do of many fossil groups." - Alfred S. Romer



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