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Re: Questions

At 08:30 AM 7/10/98 -0500, Jonathan Schmidt wrote:
>I was wondering how likely it is that "primitive" dinosaurs like
>Herrasaurus had feathers?(with the discovery of that feathered
>Dilophosaurus it seems possible that even Marasuchus could have had

What feathered Dilophosaurus?

>From my theropod review paper at the Portuguese meeting:

        At present, little is known of the integument of non-avian theropod
dinosaurs.  Where known, other groups of dinosaurs have tuberculate scales
covering most of the body (CZERKAS, 1997).  Such a condition is reported for
the neoceratosaur Carnotaurus (CZERKAS, 1997), but the (apparently
extensively preserved) integument of this form has yet to be described in
detail.  Several specimens of the basal avian Archaeopteryx preserve clear
feather impressions (see, for example, OSTROM, 1985), and feathers are
assumed to have been found in all subsequent birds (even if not preserved)
as argued by the Lagerstätten option of the Extant Phylogenetic Bracket
method (WITMER, 1995).
        The phylogenetic distribution of feathers or feather-homologues has
been debated in the past (BAKKER, 1986; PAUL, 1988, 1994).  In recent years
discovery of the integument of several small, exceptionally well-preserved
coelurosaurs has helped to provide some new data to this debate.  These
include the type specimen of Pelecanimimus polyodon PÉREZ-MORENO,
the ?maniraptoriform Protarchaeopteryx robusta JI & JI 1997 and the type and
referred specimens of Sinosauropteryx prima JI & JI 1996 (see also CHEN,
DONG & ZHEN, 1998).
        The integument of Pelecanimimus was originally described as being
composed of two sets of subparallel fibres, one system arranged
perpendicular to the bones, and a second fainter system parallel to them
(PÉREZ-MORENO et al., 1994).  However, reexamination of these structures
suggest these are not external features, but instead represent
three-dimensionally preserved internal features of the skin and muscle
tissue (BRIGGS et al., 1997).  As such, they do not illuminate the external
covering (scales or otherwise) of this early ornithomimosaur.  The only
external surface impression reported by BRIGGS et al. (1997) was smooth skin
lacking any visible dermal structure (e.g., feathers, scales, fibres) in the
gular pouch or dewlap underneath the throat of this animal.
        The fossils of the compsognathid Sinosauropteryx and the
maniraptoriform Protarchaeopteryx are exceptionally well-preserved in the
Jianshangou Member of the Yixian Formation, a volcanoclastic mudstone (CHEN,
DONG & ZHEN, 1998).  The integument of the former is composed of densely
packed, coarse, apparently hollow hair-like fibres.  These features may be
homologous with feathers, although they lack the complex structure of avian
feathers (even as primitive as Archaeopteryx: see, for example, FEDUCCIA,
1996).  If so, the presence of these features on a relatively primitive
coelurosaur suggests that such structures may be widely distributed among
the advanced theropods.  Skeletal evidence strongly suggests that the
various maniraptoriform clades are more closely related to birds than are
compsognathids (HOLTZ, 1994, 1996, in press a; SERENO, 1997).  Following the
Lagerstätten option of the Extant Phylogenetic Bracket method, and given
that contrary evidence (i.e., external integumentary evidence from non-avian
maniraptoriform theropods) is lacking at present, the phylogenetic structure
of the advanced theropods (Fig. 2) suggests that these integumentary fibres
are primitive for the clade composed of all descendants of the most recent
common ancestor of birds and compsognathids (Fig. 4).  If the primary
function of these fibres were for insulation, it may be that only smaller
taxa and the juveniles of the larger taxa might be expected to show these
structures (PAUL, 1988, 1994).  However, confirmation of this hypothesis
awaits discovery of the preserved external integument of theropods more
closely related to birds than are compsognathids.
        Protarchaeopteryx robusta has been described only briefly (JI & JI,
1997), and is said to have true feathers with complex internal structures.
However, the phylogenetic position of this taxon has not been analyzed at
present.  If it is more distantly related to birds than some other form (for
example, dromaeosaurids), it would suggest that the intermediate taxon (or
its immediate ancestors) also possessed these features (Fig. 5A).  If, on
the other hand, Protarchaeopteryx is more closely related to Archaeopteryx
and other birds than either are to dromaeosaurids, there would be no
phylogenetic distributional evidence to suggest feathers in the latter (Fig.
5B).  Further anatomical study of this intriguing specimen is necessary
before the phylogenetic position of Protarchaeopteryx is resolved.

Obviously, this was written before the recent redescription of
Protarchaeopteryx and the naming of Caudipteryx.

So, at present, we have at present no direct evidence of feathers or
protofeathers outside of Coelurosauria, and no phylogenetic evidence to
suggest these structures are present in anything as primitive as
Herrerasaurus.  This is not to say that new data or revisions of phylogenies
might not change these results.

Thomas R. Holtz, Jr.
Vertebrate Paleontologist     Webpage: http://www.geol.umd.edu
Dept. of Geology              Email:th81@umail.umd.edu
University of Maryland        Phone:301-405-4084
College Park, MD  20742       Fax:  301-314-9661