RE: Phil Currie celebration, tyrant skin, and other things

["Tim Williams" <twilliams_alpha@hotmail.com>]

Tom Holtz wrote:

> 2) Tyrannosaurid juveniles may have been feathered; tyrannosaurid adults
> may
> have had feathers over part of their body, but these parts haven't been
> recovered.  (Not very compelling argument, but at present only tiny scraps
> of skin smaller than a CD case have been found).

I actually regard this possibility as the most credible - especially if (as
seems likely) feathers originally evolved for the purpose of thermal
evolution.  An adult _Tyrannosaurus_, tipping the scales at 8 tonnes, may
quite simply not have needed feathers.  Perhaps adult tyrannosaurs did
retain a sprinkling of feathers over certain parts of the body, but just for
the purpose of decoration or display rather than for insulation.

I think we can confidently predict that feathers evolved in small theropods
(_Ornitholestes_-size or below), not large ones.  The very much reduced
surface area to volume ratio of an adult tyrannosaur reduced the need to
minimize endogenous heat dissipating from the body.  Tyrannosaur chicks
(being rather small) may have had downy feathers, but lost them at maturity.
 Maniraptoriform taxa that only achieved a small adult body size kept their
feathery coast throughout life.


> 3) Tyrannosaurids may have had feathered ancestors, but had reversed to the
> ancestral condition.

A fourth possibility is that feathers were seasonal: grown before winter and
shed before the arrival of warmer weather.  Of course, this depends upon
whether tyrannosaurs actually ventured into colder habitats.



Tim

------------------------------------------------------------

Timothy J. Williams

USDA/ARS Researcher
Agronomy Hall
Iowa State University
Ames IA 50014

Phone: 515 294 9233
Fax:   515 294 3163

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