Re: Follow-up: the truth about killer dinosaurs

["T. Michael Keesey" <keesey@gmail.com>]

On 8/31/05, Michael Mortimer <mickey_mortimer111@msn.com> 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.

> There's nothing about (comparatively) small flightless birds like
> Patagopteryx and Gargantuavis that leads to questioning the presence of
> feathers.

Oh, for a 5-ton avialan....

> However, we know that tyrannosaurids were at least partially
> scaled.

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.

> 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 function in
> tyrannosaurids.  Some flightless birds keep theirs for display (ostriches),
> 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.

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
evidence.

--Mike Keesey