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Re: Follow-up: the truth about killer dinosaurs
T. Michael Keesey wrote-
> Rahonavis preserves quill nodes on the ulna, so actually does preserve
> direct evidence of feathers.
Fair enough, but I can salvage my point: it has no evidence of
feathers anywhere but the wings, but nobody would restore it as scaly,
but with feathery wings.
Insulation is nearly always associated with vertebrate flight (including
pterosaurs), except for that naked bat which lives in tropical conditions.
The latter exception does lead one to ask questions though, I admit.
> However, we know that tyrannosaurids were at least partially
We also know that nearly all birds have scutellae on their feet. Yet
none have scutellae *everywhere*. Just about everything with feathers
also has scutellae, so this doesn't really tell us anything,
especially considering how small those scaly patches are.
Though none of the tyrannosaurid skin impressions has been specified to a
certain body area, are we to believe they were all pedal?
> Large mostly hairless mammals tend to keep hairs for functional
> reasons (eyelashes, tails for swatting insects, etc.). Besides display,
> remiges and retrices would appear to have very limited potential
> tyrannosaurids. Some flightless birds keep theirs for display
> some don't (emus, kiwis). Who knows if tyrannosaurids would have?
I didn't mean to suggest that tyrannosaurids had remiges or
rectrices--those seem to be present only in _Maniraptora_ sensu
stricto (i.e. sensu Sereno; node-based); _Dilong_ doesn't have them.
I'm guilty of recalling the published sillouette of Dilong, which shows
them. Turns out no forelimb feathers are preserved, and the caudal feathers
(though branched) aren't demonstrably different from Sinosauropteryx.
Again, I challenge the large, hairless mammal analogy: hairs are not
feathers and mammals are not coelurosaurs.
It is true that the only known feathers in non-maniraptorans appear to
be for insulation. But a _T. rex_ would have benefitted from
insulation throughout much of its early life, and it would be simpler
to reduce the feathers (or even just not grow them any further--let
them stay the same size and, as the animal's surface area increases,
they spread apart) as it grew bigger than it would be to molt them and
replace them with scales. Maybe that's what they did, but it seems
like a more complicated scenario than is required to fit the known
I can't picture replacing feathers with scales, but what if the juveniles
had scales with feathers in between (like opossum tails have scales and
fur), then shed the feathers perminantly on the way to adulthood. Of
course, if I'm going to posit that, I wonder if impressions of interspersed
feathers would be preserved at all in Judith River sediments (or Morrison or
La Colonia for that matter).