Re: dinos and birds

[Mickey Mortimer <Mickey_Mortimer111@msn.com>]

Jaime Headden wrote-

>   Well, as I am currently away from my references, taking a vacation in
> dry, hot Las Vegas for the 4th, I cannot confirm specimen identities, but
> at least one specimen has ventral, belly scutes.

Benton (1999) would disagree.
"However, on the dorsal cast they are definitely draped over the neural
spines, which form a faint ridge beneath them."
"Similar bands are seen in the anterior part of the trunk of BMNH R3557 and
BMNH R4823/4; these seem to confirm that the structures are dorsal and lie
above the vertebral column."

> Evidence for
> fluffy-like integument is absent despite the fine details of the bone.

The bone is not preserved, let alone in fine detail.  Instead, information
comes from casts made from natural molds.  As the teeth are the size of the
grain in which the specimens are preserved, I doubt integumentary filament
molds could be preseved even if present.  The lack of evidence for
filamentous integument is thus unsurprising.

> While this is not evident, it is also constrained by the bracketing of
> other basal archosaurs, including *Lewisuchus* and sphenosuchians, which
> show a more croc-like or irregular sagittal dermal skeleton, and in the
> latter, show no evidence of folicular invasion of the dermal bones, or
> bony growth around the folicular channel. In this case, given archosaurian
> evolution even if pterosaurs are included, *Scleromochlus* has little to
> non positive inferrence it would have a "pelage." No other tetrapod shows
> scalation in the same place as folicular activity other than scalation,
> even birds, which show feathered replacement rather than scales around the
> feet (as in ptarmigan, swifts, or some owls).

Ever seen an opossum tail?  Scales with hairs in between.  Even assuming
scutes would have to show folicular invasion if the surrounding skin was
"furry" (which I don't see as necessary), we can't tell if they do in
Scleromochlus (assuming they are scutes and not scales), and I bet the
condition's not described in Lewisuchus.  Sphenosuchians are crurotarsans,
so are irrelevent (unless you believe Peters' hypothesis).  You'll have to
bring in unfeathered non-coelurosaur dinosaurs if you want phylogenetic
bracketing to have a say in the matter of basally "feathered/furred"
avemetatarsalians.

> This, unlike other data,
> show that it is not really likely, though not imposible, that the armor in
> *Scleromochlus* included a pelage. Unlike the hairy sloths, the dermal
> armor does not occur as nodules, but as plates; as in the plated
> armadillos, hair and armor take an alternating position for the most part:
> where there is armor, there is little hair ... and where there is much
> hair, there is nil armor. This would provide that a very fluffy
> *Scleromochlus* is unlikely. IF it were a mammal -- we have no idea if any
> other animal would be remotely likely to show such a condition since there
> are no other animals aside from mammals with a non-hair folicular
> structure (aka, scale, hair, feather, nail) growing in the same place and
> region as the hair, or interspersed. This, rather than supporting a "We
> don't know any better, so all bets are off and let's draw fluffy
> *Scleromochlus* anyway" idea, and supports a "Look at plated, scaly
> animals, and if they were haired, look at animals with hair, THEN look at
> animals that don't have hair (all non-cynodonts) and see what the pattern
> THERE is..." idea. There is NO positive evidence or even "weak" inference
> to support a furred *Scleromochlus,* mammals [which it is not]
> notwithstanding.

Oh, I agree.  I like the prolacertiform pterosaur hypothesis better myself,
so doubt Scleromochlus has much to do with the latter.  And as intriguing as
psittacosaur quills are, I prefer feathers evolving within Coelurosauria.
So, being phylogetically far from both animals with feathers, and those with
'ptero-fur', there's not much reason for Scleromochlus to have either.  But
there's no morphological reason to rule it out.

Mickey Mortimer
Undergraduate, Earth and Space Sciences
University of Washington
The Theropod Database - http://students.washington.edu/eoraptor/Home.html