Re: Non-theropod dinosaurs and feathery/fluffy integument

[Jura <pristichampsus@yahoo.com>]

--- 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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