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RE: Eodromaeus, new basal theropod from Triassic in Argentina



> This would imply that scales (in crocs) and scales, feathers, and
> "hair" or bristles in birds are all homologous. As the
> squamation of crocs is assumed to be homologous to that of,
> say, the common garter or red-eared slider, we could assume
> then that squamation in Reptilia (_sensu lato_) and birds
> (and that of feathers) are also homologous.

and

> mammalian hair and
> lacertilian scales are related, making them more homologous
> than morphology implies.

And the Bat wing and bird wing are also related, they are homologous in that 
they are both derived from the same ancestral tetrapod limb.
Their modifications towards a functional aerodynamic surface (ie, a wing), are 
not homologous. Finding a tetrapod limb modified into a functional wing in both 
synapsid lineages and diapsid lineages does not give us license to suppose 
wings were widespread in the clade, and illustrate some ancestral 
reptiliomorph, known only from a jawbone, with wings.

So if feathers and "reptile" scales, and even mammal hair are derived from the 
same ancestral structure, that is really beside the point as I see it.
My question is if the modification of the ancestral state towards a filamentous 
structure, is homologous.
If the specific way that these "scales" were modified to be filamentous is not 
homologous, I think it is premature to illustrate basal dinosaurs (or 
ornithodirans) with filamentous covering.





Jaime Headden wrote:
> I argued that even
> were the morphology different, structural features of the
> development of the follicular bud and B-keratins in crocs
> and birds are more comparable than in non-archosaurs. This
> would imply that scales (in crocs) and scales, feathers, and
> "hair" or bristles in birds are all homologous. As the
> squamation of crocs is assumed to be homologous to that of,
> say, the common garter or red-eared slider, we could assume
> then that squamation in Reptilia (_sensu lato_) and birds
> (and that of feathers) are also homologous.

Followed by:


and:

>   Finally, "homology" can be used 
- On Sun, 1/16/11, Jaime Headden <qi_leong@hotmail.com> wrote:

> From: Jaime Headden <qi_leong@hotmail.com>
> Subject: RE: Eodromaeus, new basal theropod from Triassic in Argentina
> To: "Erik Boehm" <erikboehm07@yahoo.com>, "Dinosaur Mailing List" 
> <dinosaur@usc.edu>
> Date: Sunday, January 16, 2011, 6:28 AM
> 
> Erik Boehm wrote (in response to my message which is
> appended below in full):
> 
> <So then it can be definitively concluded they weren't
> merely elongated 
> scales, analogous to the "ridge" on the backs of most
> iguanas?>
> 
>   No. In my response to Jura/Jason, I argued that even
> were the morphology different, structural features of the
> development of the follicular bud and B-keratins in crocs
> and birds are more comparable than in non-archosaurs. This
> would imply that scales (in crocs) and scales, feathers, and
> "hair" or bristles in birds are all homologous. As the
> squamation of crocs is assumed to be homologous to that of,
> say, the common garter or red-eared slider, we could assume
> then that squamation in Reptilia (_sensu lato_) and birds
> (and that of feathers) are also homologous. Other work also
> indicates that keratin structures in mammalian hair and
> lacertilian scales are related, making them more homologous
> than morphology implies.
> 
>   What has been recently argued is that the follicular bod
> develops variously among these animals, either as a scale OR
> as a filament, but not one into the other. This means that
> "No," the feather is not an elongated scale, but arises from
> a spine-like papilla (forming an invaginated follicle) that
> splits and branches, forming barbs; this is structurally
> similar, then to scale formation: placode to papilla to
> follical, to mature form.
> 
>   Finally, "homology" can be used in both an absolute
> manner, where it is strictly used to designate objects which
> share a common origin; but also for a spectrum of similarity
> throughout development, through form, and via structural
> composition. In this, I favor the more absolut
solute questions; when dealing with
> homology of development, the sliding scale agrees with its
> use here between feathers and scales, but disagrees on the
> absolute use because of the form and structure conditions.
> 
> Cheers,
> 
> Jaime A. Headden
> The Bite Stuff (site v2)
> http://qilong.wordpress.com/
> 
> "Innocent, unbiased observation is a myth." --- P.B.
> Medawar (1969)
> 
> 
> "Ever since man first left his cave and met a stranger with
> a
> different language and a new way of looking at things, the
> human race
> has had a dream: to kill him, so we don't have to learn his
> language or
> his new way of looking at things." --- Zapp Brannigan
> (Beast With a Billion Backs)
> 
> 
> 
> 
> 
> ----------------------------------------
> > Date: Sun, 16 Jan 2011 01:56:22 -0800
> > From: erikboehm07@yahoo.com
> > Subject: RE: Eodromaeus, new basal theropod from
> Triassic in Argentina
> > To: Dinosaur.Mailing.List@listproc.usc.edu;
> qi_leong@hotmail.com
> >
> > >   Eventually, this issue rests on
> tiny *Tianyulong,* an
> > > ostensible heterodontosaurid with "quills" like
> that in
> > > *Psittacosaurus* on the base of the tail
> (suggesting less
> > > than a preservation restriction in the latter);
> here, the
> > > animal is also covered from neck to further down
> the tail
> > > than the "quills" in much finer filaments. They
> also appear
> > > to be hollow.
> >
> > So then it can be definitively concluded they weren't
> merely elongated scales, analogous to the "ridge" on the
> backs of most iguanas?
> >
> > (like in this picture)
> > http://upload.wikimedia.org/wikipedia/commons/thumb/9/9b/St_Thomas_Marriott_Iguana_9_cropped.jpg/796px-St_Thomas_Marriott_Iguana_9_cropped.jpg
> >
> > I haven't read the paper or seen pictures of the
> fossils.
> > Only the abstract http://www.ncbi.nlm.nih.gov/pubmed/19295609
> > Describing "long, singular and unbranched filamentous
> integumentary (outer skin) structures"
> >
> > So I was worried it came down to basically just taking
> any "bristle" looking thing, and
 look at birds and iguanas, and
> conclude bristles/fuzz are ancestral to diapsids, and
> widespread throughout diapsids.
> >
> >
> >
>     
>         
>           
>