RE: Eodromaeus, new basal theropod from Triassic in Argentina

[Jaime Headden <qi_leong@hotmail.com>]

  Jason/Jura, I do not know what was lost: My copy of the sent file appears to 
possess the truncation, so I am sorry for one of my attempts at a "proof." I no 
longer recall what I was writing, specifically.

  Jura wrote:

<The authors even go so far as to mention that the chance of homology 
with maniraptor fuzz is suspect. The material associated with 
_Psittacosaurus_ SMFR 4970 are larger and thicker still, found 
on one spot of the body only, and may not even be filamentous at all 
(i.e. they could be more akin to the dorsal spikes of iguanas).>

  There is no way to directly reject based on the hollowness or lack thereof 
that a non-hollow structure would not derived from the imminent filament that 
results in a stage 1 "feather" (re: Prum); presumably, like a scale which 
erupts from the follicle in the same fashion, this structure would either NEED 
to be hollow, or develops from a non-hollow incipient condition as both hair 
and scales do. The authors are free to make the comparison weaker based on this 
structure, and I have no objection to this. In my recent reply to Augusto Haro, 
I also mention TLS's reticence regarding the psittacosaur specimen "quills" but 
I am much less willing to accept the analysis due to various procedural issues 
I have with TLS's recent work (see 
http://qilong.wordpress.com/2009/09/22/lingham-soliars-review-of-chinese-fossil-preservation/).

<Your argument that it is more parsimonious to assume that filamentous 
integument evolved only once in Ornithodira is a bit one sided. You are 
only looking at the filaments. As I have stated ad nauseum on this list 
and elsewhere, scales are integument too.>

  I have repeatedly use the term "squamous integument" in direct relation to 
"'fuzzy' integument." I haven't even used "plumed integument" to bring the 
comparison further to extant birds. This has nothing to do with a proposition 
that filaments like that found in pterosaurs and those in *Sinosauropteryx* 
(assuming TLS is _incorrect_ that these are collagen from a frill) are the 
exact same type of structure. Kellner et al. can easily claim the variation is 
special for pterosaur "fuzz" while at the same time the relative thickness of 
the filaments has NOTHING to do with whether they may be homologous, at least 
as far as I can tell.

<A plucked bird is not scaly, 
and despite anecdotes (and pictures) of derived taxa such as snowy owls 
with feather/scale mixing, the presence of scales in birds is highly 
restricted.>

  But the assumption here is that birds derived from once-squamous ancestors. 
There must be a point, for which we have NO evidence currently, that ancestral 
pre-birds were partially squamous and partially "feathered" or "fuzzy," and at 
some point here, nonsquamous skin (face, neck, lecks, apterous regions of the 
body) develop -- possibly after the development of a true feather.

<Current evo-devo studies suggests that feathers evolved by 
hijacking the scale development pathway (Sawyer et al 2003, contra Prum 
1999 & Brush 2000), and that scales re-evolved by suppressing this 
(Tanaka et al 1987, Zou and Niswander 1996).>

   Presumably, hair, feathers, etc. all derived from scales or a similar 
squamous form in the ancestral tetrapod.

<In order for filamentous 
integument to have evolved only once, it would have to have been lost 
(and scales re-evolved) a minimum of seven times!>

  It has been argued at least mostly anecdotally that large size forces loss of 
pelage and plumage (although not squamation) in a terrestrial environment: 
ostriches at least loos pelage on the legs and neck from an ontogenetically 
more feathered condition as chicks, and do so in apparent reaction to lifestyle 
and habitat. Any other large bird that reduces plumage in a body region does 
this just as convergently (and for different reasons: see vultures). For hair, 
Paqchydermata was coined to group the large-bodied, hairless mammals, but it is 
acknowledged that these are all independant losses of hair, while whales may 
imply that additional hairlessness could have been serially acquired as they 
took to the water. It then becomes problematic to assume that serial loss in 
relation to phylogeny is not unparsimonious.

  My original use of the term parsimony and reference to Phylogenetic 
Bracketing was based solely on structural similarity as compared to phylogeny. 
Homology in unproven, and merely objecting to a debated homology does not 
reject the argument I made, even if it seeds doubt (this I concede). Instead, I 
might as easily question the homology of various squamous-like structures, as 
we can easily then claim that the fantastic things *Longisquama* sports 
non-squamous in any relation, or that in addition because hair, scales, and 
feathers are all derived from integumental follicles, they are all essentially 
homologous while being structurally distinct (this makes "dinofuzz," 
"pycnofibres" and hair homologues on a structural level as well).

  I might also re-clarify that my argument presumed multiple positions for 
pterosaurs: It does not assume that Ornithodira must exclude *Crocodylus* (be 
extension of the definition). Rather, it makes an argument towards application 
of the appearance of the fibres and their assumption (primarily within 
theropods) that they are all homologous with each other. Even n theropods, one 
may question this assumption as the different structural qualities are only 
presumed homologous because they are found throughout the same animal and some 
bear similarities to some stages of feather development; not all of them do, 
and Prum's hypothetical progression may be more simple than the truth, and thus 
reduces its own explanatory power for animals that may have variously developed 
branching filaments from an homologous single-strand filamentous structure. 
This is even more problematic when you throw "elongated broad filamentous 
feathers (ebff)" into the mix, which may be distributed between non-avian and 
avian forms without any direct phylogenetic connection between them but are 
otherwise identical.

  Strict application of the homology-only version of this parsimony game, would 
tell us that we are totally clueless and only our previous assumptions about 
the relationships of birds to "reptiles" inform us against these biases. 
Parsimoniously, we should assume initially that similar form result in similar 
function unless otherwise indicated; those "otherwise indicators" are not 
showing up, but instead the varieties of form being presented are increasing, 
and this can just as easily (like the supposed ebffs) result in false-signaling 
of variation as "nonhomologous," and leads some authors (like TLS or Kellner) 
to object to any apparent structural variation and cry "nonhomologue means not 
related!"

  Under the assumption, then, that these taxa are related, and that similar 
structures arise from similar follicles, we can infer that these structures ARE 
homologous. Parsimony, then, tells us that *Dinosauria* presents a 50% or 
greater likelihood to assume a given fossil for which the evidence is not 
present to bear some form of filamentous-like integument. Not that it was 
covered head-to-toe in it (which Jura should also note I never said, nor was it 
seemingly assumed by Sereno et al.), but that it _had_ it.

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)