RE: Eodromaeus, new basal theropod from Triassic in Argentina

[Jaime Headden <qi_leong@hotmail.com>]

Erik Boehm wrote:

<Is there anything to suggest that the *Psittacosaurus* "quills" are
 not simply elongated scales? then it just becomes a question of if 
scale length can vary significantly.

Still, it doesn't 
seem to be "fuzz", *Psittacosaurus* was pretty small (and small size 
would presumably make fuzz more beneficial).

I didn't think there was evidence for "fuzz" on any dino outside Tetanurae. If 
pterosaur fuzz isn't homologous, I still think that early dinos probably 
weren't fuzzy.

If the ptero "pycnofibers", "Psittacosaurus quills", and maniraptor 
"dinofuzz" are all homologous, then I withdraw my objection.

However, I thought the consensus was that there is no/insufficient evidence 
that they are homologous.>

  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. The position of 
Heterodontosauridae (if it belongs) has been debated and includes basal to the 
*Eurypoda-Cerapoda* split in *Ornithischia*, as well as withing *Cerapoda*, 
basal to *Marginocephalia* (equivalent to being a member OF *Marginocephalia*) 
or basal to a clade within *Marginocephalia*, such as *Ceratopsia* -- which is 
where *Psittacosaurus* lies.

  Regardless, were these structures identical to stage I protofeathers as 
observed in *Sinosauropteryx* and *Dilong*, then it supposes a broadened 
expression across *Dinosauria*. One may also infer that they converged into 
similar conditions, so that basal ornithischians and some theropod dinosaurs 
developed them independantly. Should this be the case, it stresses the 
expression of a filamentous integument repeatedly within *Dinosauria*, and 
invokes the same level of incredulity Jura/Jason raised as being lost that many 
times.

  My argument thus far does not insist that certain things were true, or even 
homologous, but that the prevalence of a similar type of integument in an 
ornithischian and a theropod projects a sense of prevalence across the base of 
*Dinosauria*. It thus matters not that these structues could be lost (even 
repeatedly, as is the case with complex pennaceous or flight feathers in 
various birds towards lineages that convergent loss powered flight and develop 
features that are similar but assumed convergent due to relation to 
flightlessness), only that they would seem to be present across small-bodied 
animals on different branches of the dinosaurian tree.

  As I said before, the only way to test this is to prove that fossil forms 
betwene these taxa did not have this integument, while (say) operating at the 
same apparent age and size classes present in the forms studied (when known).

---

  Mea culpa: Previously I stated that I had indicated that squamous and "fuzzy" 
integument could be present on the same form at the same time. Tom Holtz caught 
this, and Jura/Jason responded on this issue, and I had missed it. My actual 
text does not state that there was a possibility for both simultaneously and 
the quoted text which Jura/Jason responded to did not have this caveat in it. I 
apologize for this, as it indicates sloppy writing on my part and likely led to 
confusion with Jura/Jason in our previous exchange.

[In my defense, however, I had listed taxa which preserved both forms in one of 
my emails on this subject, but again, it was not in the main body which is the 
quotable part anyways.]

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)