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2
The University
of Kansas Paleontological
Contributions
Institutional abbreviations cited: FIP, Florida Institute
of Paleontology, Dania
Beach, Florida; KUVP, The
Univer-
sity
of Kansas
Natural History
Museum and Biodiversity
Research
Center,
Lawrence, Kansas; SMM, The Science
Museum of Minnesota,
St.
Paul, Minnesota.
SYSTEMATIC PALEONTOLOGY
Terminology follows Weishampel, Dodson,
and
Osmélska
(eds., 1990), except that
the semilunate
carpal is
not referred to
as the radiale.
DINOSAURIA Owen, 1842
THEROPODA Marsh, 1881
MANIRAPTORA
Gauthier, 1986
DROMAEOSAURIDAE Matthew
and Brown, 1922
BAMBIRAPTOR n.
gen.
Type species.—Bambiraptor feinbergi
n. sp.
Diagnosis.—Jugal
with row
of
foramina along
ventral
margin;
scapula with
large,
medially directed
acromion;
distinct, short scapulocoracoid suture; coracoid
with neck
or
peduncle forming
part of glenoid; coracoid
foramen
absent; 13 dentary teeth, 9 maxillary teeth; ratio of hu-
merus
plus
ulna to
the
femur
large (H+U/F = 1.68); pubis
with distal shaft
and
boot rotated posterodorsally; ischium
with small
proximal
dorsal
process;
femur strongly recurved
laterally
and
posteriorly.
Remarks.—Genus
presently contains a single
species.
BAMBIRAPTOR FEINBERGI n. sp.
Figure
1-8
Velociraptor
sp.
cf.
V.
langstoni
(Sues); Burnham, Derstler,
and Linster, 1997, p. 75.
Velociraptor
Feduccia, 1999, p. 380.
Diagnosis.—As
for
genus.
Description.—The
holotype skeleton
of
Bambiraptor
feinbergi
has
an estimated length of
one
meter. It is
a
lightly
built theropod
(Table 1),
with
proportions more
similar to
those
of
Archaeopteryx lithographica
(Table 2)
than other
known theropods. The holotype
is roughly twice
the
size
of
the Berlin
Archaeopteryx
(De Beer, 1954), but the
head is
two
and one
half times
as large (12 cm
vs. 4.8
cm).
The
skull
of the holotype
is virtually complete
(Fig. 1).
It is lightly built with
a
narrow snout
and large,
dorsally
inflated braincase. Additionally,
the
skull has
large
upper
temporal
openings, T-shaped lacrimal,
long
narrow frontals
with pronounced
orbital rim, large antorbital fenestrae,
maxilla with 2 accessory fenestrae,
and 9
sharply recurved
teeth up to 6 mm
in
length. There
are 4.3 denticles per
millimeter,
but
anterior denticles
are visible on
only
a
few
teeth. They
are more
closely spaced (6.0 to 6.5
per
milli-
meter)
and
smaller.
The premaxilla
contains 4 alveoli,
but
the
tooth crowns
are
broken
and
mostly missing. Jugals
are
long and
parallel sided with
a
row
of
small, ventrally posi-
tioned foramina along
the ventral margin. The
ascending
process
of the jugal
is inclined posteriorly at nearly 45
degrees.
Table 1. Lengths
(in mm) of
selected elements
of the
holotype
Bambiraptor feinbergi
(FIP 001) and
Bambiraptor
adult bones
(new).
skull
125*
mandible
121*
right scapula
87
left
coracoid
40
left
sternum
69
five
sacral
vertebrae
60
left humerus
105
left ulna
95
left metacarpal
II
48
three
phalanges of
left manual
digit II
85
left
ilium
85
left
ischium
52
left
pubis
105
left femur
119
left
tibia
168
left metatarsal
III
78
four
phalanges of
left pedal
digit III
76
adult femur
170
adult humerus
145
adult
tibia
225
adult metatarsal
III
105
*estimated.
The holotype
includes two elements seldom recorded
in theropods. The
first is
a
hyoid.
This
slender rod is 3
cm
long and
nearly straight. It was preserved
in the
skull
block,
below
the basicranium and
between
the
mandibular
condyles of the two quadrates.
The
other is
the
right stapes.
A portion of
this delicate bone lay
in position
against
the
right exoccipital.
A paraquadratic fenestra is framed by
a
reduced, for-
wardly deflected
bar of bone. This bar
is formed by
the
ascending process
of the quadratojugal and the
descend-
ing process
of the squamosal.
It is slender
and
nearly
threadlike
in
B.
feinbergi.
The quadratojugal portion of
this
bar
is curved.
The
quadrate has rostrolateral flanges nearly
as long as the quadrate is
high.
In
lateral view,
the
mandible is nearly parallel sided.
There
are 13 dentary
teeth, recurved
and
similar
in
size to
the
maxillary teeth with crowns nearly 7 mm
in
length.
The dentary
teeth
have 5
posterior denticles
per
millime-
ter. Anterior denticles are
not easily
discernable. The coro-
noid
process is low
and
includes
a
delicate coronoid
bone.
The
external
surface of each dentary has many small fo-
ramina, especially abundant
on the
anterior portion.
A
mandibular fenestra is present
and
heavily built. Unfused
articulars
are
present.
The
vertebral column consists of 22 presacral vertebrae,
including 9 cervicals,
a cervicodorsal, and 13 dorsal
verte-
brae.
Large pleurocoels
occur
on the cervical and dorsal
vertebrae. Posterior cervicals, cervicodorsal,
and the
ante-
rior
dorsal
vertebrae
centra bear
a ventral
keel, similar to
Deinonychus.
There
are 5
fused
sacral and 23
preserved
caudal
vertebrae.
The
posterior end of the caudal
series is
missing. Elongated zygopophyseal rods
and extensions of
the chevrons
overlap forward, producing
the
bony tail
typical
of dromaeosaurid
dinosaurs.
Burnham
et
al.—Remarkable
New
Birdlike Dinosaur (Theropoda: Maniraptora)
3
parietal
Figure
1. Bambiraplor feinbergi
n.
gen.
and
n.
sp.,
holotype (FIP 001);
I,
skull
and
mandibular elements
in
left lateral view;
2,
restored
skull
in
left lateral view;
3,
restored skull
in dorsal
view. Scale
bar:
5
cm (new).
Most ribs
and
gastralia
are
damaged.
No single
rib
or
gastralium
preserves its full length, although
the volume of
rib heads
and fragments
suggests that
the
ribcage
and
gastral
basket were originally complete. Pending further
restoration,
the
shape
of the
ribcage
must
remain conjec-
tural.
The
proximal
caudal
vertebrae
and
rod-stiffened por-
tion
of the
tail
have a
distinctly upward curve
(Fig.
2).
It is
4
The University
of Kansas Paleontological Contributions
Figure
2.
Bambiraptor feinbergi
n.
gen.
and
n.
sp.,
holotype (FIP
001),
bone map
of
Bambiraptor feinbergi
showing
the
skeletal
elements that were associated
but
not articulated.
Note the
curvature of
the tail.
Scale
bar:
10
cm (new).
difficult to determine
if
this curve is real
or an
artifact
of
preservation.
The pectoral
girdle is well preserved three dimension-
ally
and
complete
(Fig. 3.1)
except
for the glenoid
pe-
duncle
(or
neck)
of the
right coracoid.
The furcula
is
craniocaudally compressed, U-shaped,
and
lacks
a
hypo-
cleidium (Burnham
and Zhou, 1999). The caudal surface
of the
MI cula has
a
small foramen
on
each ramus.
This
furcula (Fig. 3.4-3.5)
is reminiscent
of
those seen in the
earliest birds, e.g.,
Archaeopteryx and Confuciusornis
(Chiappe
et
al.,
1999;
Zhou, 1999).
The
scapula
and coracoid are
separate, unfused ele-
ments.
The suture
between them is distinctly shorter than
almost all theropods.
As a
geometric consequence,
the
acromion
is
more
medially directed, allowing
contact
with
the furcula
rather than
the coracoid. The glenoid
portion
of the coracoid
forms
a distinct
neck, anticipating
the
avian strutlike coracoid. Additionally,
the coracoid
lacks
a
foramen
and
has
a
prominent biceps (or coracoid)
tu-
bercle.
The glenoid faces
laterally.
Two
large, subrectangular sternal plates lie
along
the
posterior edge
of the coracoids.
Each
plate
is roughly 18
square
centimeters,
more
than twice
the
size of
the
adja-
cent coracoid. The plates are
thin except along the
cranial
margin,
where they
are
thicker
and
bear
a
groove
for the
insertion of the coracoid. The plates
also
have
articular
facets
for
at least 4
ventral
ribs.
The
forelimbs
are
essentially
as in
Deinonychus antirrhopus
(Ostrom, 1969b), although they
are
proportionally longer
(Table 2). The
wrist contains at least two elements, includ-
ing
a semilunate and a
carpal with two saddle-shaped fac-
ets
and a concave
distal
face. At least one other small
element may also be
a
carpal. Unfortunately, ambiguities
in the
bone map leave
the original position of
these bones
unresolved.
The pelvis
resembles that
of
Deinonychus antirrhopus
and
Velociraptor mongoliensis
(Fig. 4). The postacetabular
half
of
the ilium
is
compact and
tapers posteriorly.
The pubis
is
retroverted, with
a
heavy, posteriorly projecting pubic
boot.
The
pubic symphysial
suture
extends along less than 50
percent
of
the
pubic shaft (Table 2). The
distal
end
of
the
pubic shaft is deflected posteriorly.
The ischium
is
long
(half
the
length
of the
pubic shaft)
and flat. The obturator
process is located near
the
distal extremity of the ischial
shaft. There is
a
modest proximodorsal
process.
The
femur has
a
pronounced curve
and
lacks
a
fourth
trochanter. The remainder
of the hindlimb
elements
are
as
those described
for
D. antirrhopus
(Ostrom, 1969b,
1976b).
Several features indicate that
the holotype
is subadult:
neural arches unfused
to
the centra,
separate braincase
elements (notably
the
parietals), modest
sagittal
crest,
unfused posterior interdental
plates on the dentary
and
maxilla, large
orbits,
and
skull
longer
than the
femur.
Judging from lengths
of
larger isolated
Bambiraptor
limb
elements found at
the
same locality
(Table 1), the holo-
type has reached 75
percent of
its adult
size.
Incidentally,
the collection of
Bambiraptorpieces
includes
almost 40 other bones that
are
indistinguishable from
equivalent elements
in the holotype
except
for the size.
These represent at least 2 larger individuals. Among these
bones
are
several articulated, dorsally bent
caudal
series.
Remarks.—The
original preparators removed most
of
the
limb
and
girdle elements from the matrix,
as
well
as
portions
of the axial
skeleton
and
skull. When
the
fossil
was turned over to
the senior author, only three
portions
of the
skeleton remained
in
small blocks of
rock—most
of
the
skull
and
anterior
cervical
series,
portions of the
ante-
rior torso with
the sternals, and the
posterior torso with
portions of the
hips
and proximal tail. Articulation
within
each
of
these blocks was recorded by photographs,
draw-
Table 2. Ratios of
lengths
of
skeletal features;
E
femur; H,
humerus;
Pl,
pubic length;
Ps,
pubic symphysis (new).
(Tibia:F) (H+Ulna:F) (ManusILF)
(Ps:PI)
Archaeopteryx
1.42
2.11
1.42
0.43
Bambiraptor
1.39
1.68 1.13
0.54
Unenlagia
1.13
--
0.63
Sinornithosaurus
1.65
1.03
0.62
Velociraptor
1.07
0.93
0.5*
Deinonychus
1.10
1.38
1.05
<0.58
*estimated.
Burnham
et
al.—Remarkable
New
Birdlike Dinosaur
(Theropoda: Maniraptora)
a
2
Figure
3.
Rambiraptor feinbergi
n.
gen.
and
n.
sp., holotype (FIP 001); /,
pectoral
girdle
in
right oblique anterior view; scale
bar:
5
cm;
2,
right humerus
in
external view;
3,
right humerus
in
dorsal view;
4,
furcula
in
cranial view; 5, furcula
in caudal
view; scale bar: 5 cm
(new).
ings,
and in
some
cases,
casts. Judging from these
blocks,
the
skeleton was at least partly articulated.
One of the
excavators,
Robert
Linster,
skillfully recon-
structed
a
bone map from his family's lab
notes.
Using this
map,
it appears that many
of the
bones shifted
position a
few centimeters so that much of the skeleton became slightly
disarticulated
before
final
burial. Unfortunately,
the
pre-
cise
position of some elements, notably
the
carpals, tarsals,
furcula,
and
anterior
presacral
vertebrae (including ele-
ments of
the
axis
complex) have
been lost, so their posi-
tions
on the
bone map
are
only approximate. Further-
more, almost all rib
and
gastralia
positions are
lost
and
so
they have been left off the
bone
map. At
least
one
bone
(a
left metatarsal, field number
20)
is recorded
in
two differ-
ent positions on
the
bone map
and the
right femur origi-
nally lay beneath the
pelvis,
rather than
the position
shown
in Figure
3.
Finally,
as far as
we
know, the positions of the
adult
Bambiraptor
bones
are
unrecorded.
The
individual skull
blocks
were pieced together before
final
preparation. Unfortunately, many of
the
skull ele-
ments sustained
damage
during excavation
and
initial
preparation. Many were split
and
pieces were missing. The
occipital
region
and
skull roof were especially damaged. It
is
impossible
to determine
if the
two missing skull bones—
the right
premaxilla
and
supraoccipital—were
present
in
the
outcrop.
The
vertebral column suffered
damage as well.
Some
vertebrae were partly
disarticulated
and
crushed by sedi-
mentary compaction.
Most
presacral
vertebrae were re-
moved
and
further damaged before
the
senior author
received
the
fossil.
The
first 16 caudal
vertebrae
are
articulated
and intact.
Portions of
at least
6
(and
probably
8)
more
exist,
all
but
1
with fresh
breaks
indicating that they were originally more
complete
in the rock.
By studying
the
size
of
these ele-
ments
and the
size
of the
zygapophyses,
we conclude that
6
The University
of Kansas Paleontological
Contributions
Figure 4.
Bambiraptor feinbergi
n.
gen.
and n.
sp., holotype (FIP 001), pelvic girdle
in
lateral view. Scale
bar: 5 cm (new).
Bambiraptor feinbergi
originally had
more
than 22
caudal
vertebrae, some
of the
additional ones being located be-
tween
the
existing bones
and
others distal to
the
preserved
end of the
series. Unfortunately, we
have no
way to deter-
mine
the total number of caudal vertebrae
or the length
of
the
complete
tail.
Limited
information suggests that
the holotype
may
have
been a male (P.
Larson, personal
communication,
February 2000).
The
first
chevron
is
long, slender,
and
it
reclines against
the ventral side
of the
vertebral column.
The
distal
chevrons are more
bladelike
and
less reclined.
This
is reminiscent
of the condition
seen
in male
crocodil-
ians (Larson, 1995).
Bambiraptor
was possibly
a subadult
male.
The
new species is readily identified
as a
member of
the
Dromaeosauridae.
It fits
the dromaeosaurid gestalt
with its
lesser
trochanter
Burnham
et
al.—Remarkable New Birdlike Dinosaur
(Theropoda: Maniraptora)
7
enlarged, retractable
second
pedal ungual, rod-stiffened
tail, and
T-shaped lacrimal.
Although nearly contemporaneous with
Saurornitholestes
langstoni
(Sues, 1978), the
new taxon is distinguished by its
relatively long, anteriorly tapering
frontal.
While this fea-
ture may be exaggerated
due
to
the
immaturity
of the
holotype,
it is unlikely to be entirely
an ontogenetic
differ-
ence.
The frontals in the holotypes of
both species
are
nearly
the
same length,
but the orbital rim of
B.
feinbergi
is
twice
as long
as
that
of
S.
langstoni.
There is little basis
for
further comparison since
the holotype of the latter
is so
incomplete and poorly preserved.
As
mentioned above,
the
limbs
and axial skeleton
of
B.
feinbergi
are
similar to those described
for
Deinonychus
antirrhopus
(Ostrom, 1969b).
This
may reflect
the
quality
of
information available
on
these two dromaeosaurids,
since
the
forelimbs (and especially
the
hands)
are
propor-
tionally
much
longer in the
new species. These two species
can be distinguished, however, by more teeth
in the
max-
illa (15 vs. 9)
and dentary (14
to 15 vs. 13) of
D.
antirrhopus.
Additionally, there
are
numerous differences
in the
shoul-
der and pelvic girdles.
Most
prominent
in
D.
antirrhopus
are the
relatively long scapulocoracoid
suture and the
less
strutlike shape of
the coracoid, a
less
distinct acromion,
lack
of a glenoid
peduncle, higher
(and
less tapered)
postacetabttlar iliac blade,
and the
larger size
and more
proximal
position
of
the obturator
process
on the ischium.
Bambtraptor feinbergi
is different from
Velociraptor
mongoliensis
(Osborn, 1924) since
the holotype
does not
have the
ventrally depressed nasals
or the
resulting bul-
bous snout (Barsbold
and Osm61ska, 1999). V.
mongo/iensis
has several additional maxillary teeth.
The furcula
is V-
shaped with
a
rounded
cross section as
well
as a
small
hypocleidium, different from
the more
Archaeopteryx-like
condition
of
Bambiraptor
(Norell, Mackovicky, and Clark,
1997). The
pectoral girdles
in the
described skeletons
of V.
mongoliensis
(Norell and Makovicky, 1999) are imperfect,
but they appear to
have a longer scapulocoracoid suture
(fused in
the
available specimens)
and a smaller acromion.
The postacetabular
blade
of the ilium
is higher
(as in
Deinonychus)
and
less tapered (Norell
and Makovicky, 1997).
Finally,
the
femur
of
Velociraptor mongoliertsis
is reported to
have a
fourth
trochanter, a
feature
absent in
Bambiraptor
and
other dromaeosaurids. Additionally
the
femur
of V.
mongoliensis
is curved
in
lateral view similar to
the holotype
of
B.
feinbergi,
but in
posterior view it is straight.
In
B.
feinbergi,
the
femur is also curved
in
posterior view
(Figure
5).
Two other Mongolian theropods
have
been described
as dromaeosaurids,
Adasaurus mongoliensis
Barsbold (1983)
and
Hulsanpes perki
Osm6lska (1982).
They may very well
belong within
the Dromaeosauridae, but
each was described
from
a single
fragmentary skeleton.
Adasaurus
was illus-
trated (Barsbold, 1983, fig. 24) with
a pubis
that is retro-
verted, but
the
distal end is not bent posteriorly
and the
ischium
has
a midshaft obturator process. The anterodorsal
Figure
5.
Bambiraplor frinbergi
n.
gen.
and
n.
sp., holotype (FIP
001);
1,
left femur
in
lateral view;
2,
left femur
in
posterior view;
scale
bar:
5
cm
(new).
projection
on
the ilium
is unlike
the holotype of
B.
feinbergi.
Hulsanpes
is too incomplete to allow meaningful compari-
son with other dromaeosaurids (Barsbold
and Ostnélska,
1999, p. 215).
Achillobator giganticus
(Perle, Norell, and Clark, 1999)
is
described from
a single,
fragmentary skeleton. The bones
present
a
mix
of
features, with only
a
few found
in
better-
established dromaeosaurids.
For
example, two pedal
unguals could come from
a dromaeosaurid-type
second
pedal
digit. On the
other
hand, the ilium, ischium,
max-
illa,
and caudal
vertebrae share
no
unique features with
the Dromaeosauridae.
It may well be that this taxon is
based upon
a mixture of
bones from two
or
more actual
species.
In
any event,
the
femur
of
A.
giganticus
is relatively
straight, there is
an
anterior projection
on the
pubic
boot,
and the ischium
has
an obturator
process that is far
larger
8
The University of Kansas
Paleontological
Contributions
Burnham
et
al.—Remarkable
New
Birdlike Dinosaur
(Theropoda: Maniraptora)
9
10
The University
of Kansas Paleontological Contributions
and more
proximal than analogous features
in
B. feinbergi.
Even discounting
the
size difference,
A. giganticus
cannot
be confused with
the
species described herein.
Comparisons
of
Dromaeosaurus albertensis
(Matthew
and
Brown, 1922; Colbert and Russell, 1969;
Currie, 1995) with
B. feinbergi
show the jugal in
D. albertensis
is
more
robust
and
lacks
a
row of ventral foraminae. Furthermore,
the bar
formed from
the
descending process
of the squamosal and
ascending process
of the quadratojugal
is
more robust,
straighter,
and
more nearly
vertical.
Perhaps most striking
are
differences
in the frontals and
tooth crowns.
The
frontals
of
D. albertensis
are
relatively
short, and the
teeth
have carinae
that follow
a nonplanar
path along
the
length
of the
crown.
The
Early Cretaceous
Utahraptor ostrommayi
(Kirkland,
Burge, and Gaston, 1993)
is described from a
small
set of
scattered theropod bones. We see little reason to believe
that these bones come from
a single
species,
let
alone
a
dromaeosaurid.
Pending
a
thorough analysis
and rede-
scription of
this material, we suggest that
B. feinbergi
can be
distinguished from
U. ostrommayi
in
its smaller size
and the
deeper popliteal fossa
on
its distal femur.
Bambiraptor feinbergi
(Fig. 6-7)
does share many features
with
the
recently described
Sinornithosaurus milleni
(Xu,
Wang, and Wu, 1999). Most
noteworthy
are the furcula
and sternal plates. This
Early Cretaceous
form,
however,
lacks
a
pubic boot
and
has a long obturator process.
Its
skull is
longer
than its femur,
and the
arms
are
proportion-
ally shorter, although these may be ontogenetically
influenced features. Contrary to
the
published descrip-
tion,
the coracoid and
scapula
are
similar to
Deinonychus
and
quite unlike those
of
Bambiraptor
described above.
Finally, we
compare
Bambiraptor
with
Rahonavis ostromi
(Forster
et
al.,
1998a, 1998b)
and
Unenlagia comahuensis
Novas
and Puerta (1997). Even though neither is
a
dromaeosaurid,
both share features with
Bambiraptor
feinbergi.
All three
have pectoral and
pelvic features other-
wise reported only
in
birds (see
Discussion
below). Both
can be distinguished from
B. feinbergi
by their lack
of a
ventrally flared preacetabular blade
on the ilium.
Further-
more, the preacetabular portion of
R. ostromi
is not flared,
and the
pubic boot projects posteriorly less than twice
the
thickness
of the
pubic shaft.
Our
new species can be differ-
entiated from
U comahuensis
by pubic shafts, which
are
joined along more
than 50
percent of their length
and
have
posterior dorsals with relatively small pleurocoels.
Etymology.—Bambi:
from
the
now widely used nickname
for the holotype,
originally coined by
the Linster
family;
raptor:
robber;
Feinberg:
honoring Michael
and
Ann
Feinberg, who recognized
the
significance
of
this fossil
and have
generously encouraged our
research and the
preservation
of
this fossil for
science.
Holotype.—FIP
001, on
exhibit at
the
Florida Institute
of
Paleontology,
Graves Museum of Archaeology
and
Natural
History, Dania Beach, Florida;
casts
are
available at
the
University of Kansas
Natural History
Museum and
Biodiversity
Research
Center,
Lawrence, Kansas (KUVP
129737) and
at
the Science Museum of Minnesota,
St.
Paul,
Minnesota (SMM P99.3. 1c).
Additional material.—FIP
002-036. Elements from
the
adults (Table 1)
discovered within
a
few meters
of the
holotype.
These
are
available
in the collections of the
Florida Institute
of
Paleontology at the Graves Museum of
Archaeology
and
Natural History, Dania
Beach, Florida.
Stratigraphy.—The
holotype came
from
the
Two Medi-
cine Formation approximately two-thirds
of the
way above
the base
of
the unit,
Upper Cretaceous, Campanian
(Lorenz, 1981; Lorenz and
Gavin, 1984).
Locality.—The
site
is about 19 km
west
of the
city
of
Bynum, Teton County,
Montana, USA.
The holotype
occurred within
a
60-cm-thick siltstone
layer
associated with thousands
of
bones
and a
few
partial
skeletons
of hadrosaurs, presumably
Maiasaura peeblessorum
(Homer
and Makela, 1979).
Also associated were at least
three specimens
of tyrannosaurids,
two
types of
eggshell
fragments, and
carbonized wood scraps. Brandvold,
Brandvold,
and
Sweeney (1996) interpreted the site as a
low-velocity channel fill within
the
Two
Medicine fluvial
complex.
DISCUSSION
The main
purpose
of
this contribution aside from sys-
tematics
and a
preliminary
description
is to identify some
of the more
obvious avian features
of
Bambiraptor feinbergi.
This
subject has become
relevant
since
the
dinosaurian
origin
of
birds was re-examined by Ostrom (1973).
Furcula.—Many
theropods have a turcula (Chure and
Madsen, 1996),
one of the
traditional hallmarks
of a
bird.
Among these wishbone-bearing animals,
Bambiraptor
is
unusual
in
having
a furcula
that has thick, curved arms,
and a
rounded interior
angle, and
lacks
a hypocleidium.
The
authors
are
aware
of
only
one
dinosaur
—
Sinornithosaurus—and
a
few early
birds—Archaeopteryx
and
Confuciusornis—that
have the same
type
of wishbone. Other
theropods
have a furcula
with straight arms
and a
less
rounded interior
angle,
while most other birds
have more
slender furcular arms and a large,
platelike hypocleidium.
Large
ossified sternum.—In
general, birds
have a large
sternum
produced from two fused
ossifications.
Bambiraptor
has two
large sternal ossifications
although they
are
not
fused. Several other maniraptorans
have
similar ossified
plates
including
Velociraptor, Sinornithosaurus,
and
Oviraptor
(Barsbold, 1983).
Laterally facing glenoid.—As
discussed by Novas
and Puerta
(1997) in
their
description of
Unenlagia comahuensis,
a
lat-
erally oriented glenoid is
a preadaptation for
avian flight.
In
all dromaeosaurids,
the glenoid faces
laterally to some
degree.
In
Bambiraptor
the glenoid faces more
laterally
than
in
any other theropod.
Elongate coracoid.—Perhaps
the
most notable feature of
Bambiraptor
is
the
shape
of its coracoid. Loss
of the dorsal
edge
of the coracoid (and
resulting loss
of the coracoid
Burnham
et
al.—Remarkable
New
Birdlike Dinosaur
(Theropoda: Maniraptora)
11
12
The University
of Kansas Paleontological Contributions
foramen) shortens
the suture
with
the scapula. The glenoid
portion
of the coracoid
becomes
a
slender neck.
Most
modern
birds
have
elongated
the coracoid in
this direc-
tion
as well, and all
have an
extremely
long coracoid
neck.
Acromion.—Reduction
of the dorsal
edge
of the cora-
coid, as
discussed above, produces
a free acromion. In
birds, such
a free acromion contributes to
the
construc-
tion
of the triosseal canal.
Bambiraptor
has
a
prominent
free acromion, as do
Unenlagia, Rahonavis,
and modern
birds. It is curious that some early birds lack
a
pronounced
free acromion
(Confuciusornis sanctus,
as
described by
Zhou,
1999),
while others
have
such
a structure
(e.g.,
Ambiortus
dementjevi
and
Otogornis genghisi
as redescribed
by
Kurochkin, 1999).
Biceps tubercle.—Bambiraptor
has a large biceps
tubercle,
as do
many other smaller theropods.
One
example among
many is
Gallimimus bullatus
Osmôlska, Roniewicz, and
Barsbold (1972). In
birds,
an
enlarged
version
of
the
bi-
ceps tubercle is termed
an acrocoracoid and
forms
part of
the triosseal canal
(Ostrom, 1976a).
Elongated arms
and manus.—Bambiraptor
has proportion-
ally
longer arms
and
hands than any other described
theropod, approaching forelimb proportions of
Archaeop-
teryx
and
other early birds.
Large semilunate
ea
.—This
bone allows
the
develop-
ment
of a
laterally folding wrist.
In
birds, except
Archaeop-
teryx,
the semilunate
is fused
on the proximal ends of the
middle
metacarpal.
The
same
condition
is found
in
most
maniraptoran dinosaurs. Recently,
a
small semilunate has
also been found
in an allosaurid (Chure, in press).
Proximodorsal
process
on the ischium.—Among
dinosaurs,
this feature is reported only
in
Rahonavis, Unenlagia,
and
Bambiraptor.
It is also seen
in
such early birds
as
Archaeop-
teryx,
Confuciusornis,
and
Cathayornis
(anterior anterodorsal
process
of Zhou, 1999).
Retroverted pubis.—Widely
discussed
in the
literature
and
present
in
all dromaeosaurs including
Bambiraptor.
This
condition
is easily observed
in
all
modern
birds, although
the
pubic shafts
have
separated.
Splintlike fibula.—In
birds,
the
fibular shaft is thin
and
tapers to
a point
before it reaches the calcaneum. In
all
dromaeosaurids including
Bambiraptor,
the
fibular shaft is
thin although it does extend to
the calcaneum.
Pneumatic cervical
and dorsal vertebrae.—Pulmonary
air
sacs are an
integral
part of the unique
avian respiratory
system.
One set
of air
sacs
grows into the
vertebrae, entering
through pneumatic fossae (pleurocoels)
on
either side
of
each centrum. Crocodilians
have a modest version of the
axial air sac (Britt, 1993)
along
the
most anterior portion
of
their vertebral column. A more extensive
system
apparently existed
in theropods,
associated with pneumatic
fossae
in the cervical and
anterior
dorsal centra
(see
O'Connor, 1999 for a
partially contrary claim).
The
holotype of
B. feinbergi
has
large pleurocoels
along
the
entire length
of the cervical and dorsal
series. They
are
similar to those found
in
other dromaeosaurids
and
birds.
ACKNOWLEDGMENTS
We thank Wes Linster, who discovered
the holotype;
Robert Linster for
reconstructing
the
bone
map; and the
entire family
of
Cliff
and
Sandy Linster, CJL, Inc.,
for
bringing Bambi to our
attention and for
graciously donat-
ing their other
Bambiraptor
bones to
the
Florida Institute
of
Paleontology. We also acknowledge
the
following colleagues
for
their
contributions
to this
project: Pat
Redman
for
producing many
illustrations; Mary Tanner for
prelimi-
nary
figures;
Larry
Martin for
anatomical
insight on
fossil
birds
and
dinosaurs
and for
reviewing
the
manuscript;
Desui Miao
for
reviewing
the
manuscript;
Marty Shttgar
for
invaluable organization;
and
Peter Larson
and Robert
Farrar
for
laboratory advice
and observations on archosaur
sexual
dimorphism.
Dave Buzzanco
and
Will Snyder helped
with
the
laboratory work.
Bill
Mason
of
Uncommon Con-
glomerates, Inc., donated
supplies.
Rhonda Friga, Crystal
Mark,
Inc., donated
supplies and lent
equipment.
Paul
Janke,
Pan Terra,
Inc., provided
digital records.
We also
thank
Bill Fleming and
Susan Turnbull, who captured our
vision on
film.
This
work was supported by Michael
and
Ann Feinberg,
Fossilworks, Inc.; Jim
and
Debbie Kendrick; The University
of Kansas; The University of New Orleans; Richard and
Maisie Wolszon;
and
anonymous donors. Peggy
Williams,
Kristen
Davis, and
Katrina Gobetz read early
versions of
this paper
and
suggested many improvements.
Burnham
et
al.-Remarkable
New
Birdlike Dinosaur
(Theropoda: Maniraptora)
13
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