Re: Sinornithosaurus millenii Xu, Wang & Wu, 1999 (featherydromaeosaurid)

["Ralph W. Miller III" <gbabcock@best.com>]

The following provides some information contained in the article, "A
dromaeosaurid dinosaur with a filamentous integument from the Yixian
Formation of China," by Xing Xu, Xiao-Lin Wang, and Xiao-Chun Wu, published
in _Nature_ 401, September 16, 1999, pp. 262-266:

The genus name is derived from Sino + Ornitho + Saurus, for " a bird-like
dinosaur from China;" the species name comes from "Millennium," in reference
to the specimen's discovery near the end of the twentieth century.

The specimen is small for a dromaeosaurid, with a skull which measures
approximately 13 cm (5 1/8 ") long.

The one photograph in the _Nature_ article depicts the fossil slab as a
whole.  The caption (copyright Macmillan Publishers Ltd. 1999) reads:

"Figure 1  _S. millenii_, Holotype, IVPP V12811.  The posterior part of the
skull is disarticulated from the snout and lower jaws and turned 180 degrees
in the opposite direction.  The postcranial skeleton is also not
articulated, but the bones retain a close association.  Integumentary
filaments have been displaced, lacking the direct relationships to bony
elements."

In other words, the skeleton is incomplete, the bones are somewhat jumbled
and broken up, and the palate and braincase are cracked and dislocated, but
a good many well-preserved elements remain.

The morphology of the fibers cannot be discerned at this time, but the
structures are described as comparable to those found on other theropods
from the Yixian Formation (and also compare with the downy integument
associated with _Confuciusornis_ fossils) and the filaments likely covered
much of the animal prior to postmortem disturbance and burial.

_Sinornithosaurus millenii_ represents the fifth non-avialean theropod genus
recovered from this locale which features a filamentous integument.  Nowhere
else in the world have non-avialean theropod specimens been found which
unambiguously preserve these elusive details.

The filamentous structures are roughly 40 mm (1.6") long; those near the
cranium seem to be shorter than the postcranial fibers.  Further preparation
of the specimen could reveal more fibers.  Due to postmortem scattering of
the filaments and the current state of preparation, the holotype does not
reveal whether rectrix-like structures or remex-like structures (as seen on
_Caudipteryx_) would have been present on the living animal.

The lateral position of the glenoid (shoulder socket) would permit
elevation, rotation and adduction of the forelimbs, providing
_Sinornithosaurus_ a freedom of forelimb movement comparable to that of
_Archaeopteryx_.  The forelimbs are estimated to be 80% as long as the
hindlimbs.

The paired, ossified sterna possess a series of perhaps five costal facets
(rib attachments), implying hinged sternocostal joints, contrary to the
hepatic piston theropod respiration model proposed by John Ruben et al.
(1997).

The skull, arms, legs, scapulae, coracoids, sacrum, a manus, a pes, and the
furcula are all quite reasonably represented by the holotype, however, many
vertebrae and rib elements are missing.

There is some distal sheath material present on one of the manual unguals,
and also on one of the pedal unguals (though not on the slashing ungual
recovered).

Detailed drawings of the specimen, the skull and lower jaws, and selected
postcranial elements are provided, as is a cladogram showing the
relationships of Dromaeosauridae, including _Sinornithosaurus_, within the
derived theropods.

The paper discusses the specimen in considerable detail; interested parties
will have to see the paper for themselves.

-- Ralph W. Miller III       gbabcock@best.com