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

["Thomas R. Holtz, Jr." <tholtz@geol.umd.edu>]

> From: owner-dinosaur@usc.edu [mailto:owner-dinosaur@usc.edu]On Behalf Of
> Larry Dunn
>
>
> >From: "Thomas R. Holtz, Jr." <tholtz@geol.umd.edu>
>
> >Oh, and did get a chance to check with the tyrannosaurid skin
> impressions
> >at
> >the RTMP.  They do have mosaic scales, but these are smaller
> than those on
> >typical hadrosaurid or ceratopsid skin (actually, the
> collections specimen
> >is about as small-scaled as Gila monster scales).
>
> What does this suggest about feathers and tyrannosaurid evolution?
>

Suggests a couple of possibilities, but unfortunately doesn't resolve them
(nor are these possibilities particularly new):
1) Tyrannosaurids may lie outside the clade of _Sinosauropteryx_ + birds,
and hence split off the tree prior to the evolution of feathers.  (Some
studies based on osteology suggest this, others do not).
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).
3) Tyrannosaurids may have had feathered ancestors, but had reversed to the
ancestral condition.

Although these different models are testable, the relevant specimens to
evaluate possibility 2 and 3 (e.g., skin impressions of juvenile tyrants)
are not known yet.

                Thomas R. Holtz, Jr.
                Vertebrate Paleontologist
Department of Geology           Director, Earth, Life & Time Program
University of Maryland          College Park Scholars
                College Park, MD  20742
http://www.geol.umd.edu/~tholtz/tholtz.htm
http://www.geol.umd.edu/~jmerck/eltsite
Phone:  301-405-4084    Email:  tholtz@geol.umd.edu
Fax (Geol):  301-314-9661       Fax (CPS-ELT): 301-405-0796