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NUMBER 89 281
slabs, respectively. The radius also is represented by portions
of the shaft on both these slabs (Figure 3). It shows a circular
cross section in the midshaft. The ulnare lies near the proximal
end of the carpometacarpus. This curved element exhibits just
its oval-shaped proximal portion, in which a small fossa is developed
in the place of attachment of the humerocarpal ligament.
The left carpometacarpus displays its ventral side and the
proximal articular surface (Figures 1, 3). It has a well-developed
ulnocarpal trochlea and a deep infratrochlear fossa. The
carpal trochlea appears to be small and narrow, and the extensor
process is poorly developed, in accord with Elzanowski
(1995). The pisiform process is either not preserved or is not
developed. The major metacarpal is represented by bone fragments
on the main slab and by a mold on the associated slab.
The minor metacarpal is represented by the most proximal part
of the base and by a mold of a small portion of the shaft on the
main slab. The metacarpals are completely fused at their proximal
ends. The proximal shafts of both metacarpals are similar
in size. The molds of all three phalanges of the major wing digit
are displayed on the associated slab, with the ventral sides
exposed. The proximal phalanx has a typically avian morphology,
with a flat cranial surface and a thin, flat caudal plate, with
two divided depressions on the ventral side. The intermediate
phalanx is long and thin, and it does not show a vestigial condition.
The ungual phalanx is flat, short, and slightly bowed. The
intermediate and ungual phalanges form a good articular joint
with each other.
SOME FEATURES IN THE MORPHOLOGY OF
Ambiortus AND Otogornis
One of the most characteristic properties of Ambiortus dementjevi
was supposed to be the amphicoelous cervical vertebrae,
as I had proposed in earlier publications on this fossil
(Kurochkin, 1982, 1985a, 1985b). As emphasized above, however,
the eighth and tenth cervical vertebrae are now known to
have heterocoelous centra. New observations also revealed a
contact between the broken edges of the counterslab and associated
slab. Thus, the major metacarpal, radius, and ulna in the
main slab show extension on the associated slab with specimen
PIN 3790-272 that provides certain confirmation of belonging
to the same specimen.
I have not attempted a detailed description of Otogornis
genghisi, but I mention just some corrections to the original paper
and the characters important for comparison with Ambiortus
dementjevi.
Most characters of Otogornis genghisi that are used in this
paper were published in the original description by Hou (1994).
In contrast to Hou's observations, however, I discovered that
the deltopectoral crest is present, the transverse ligamental furrow
is only expressed as a distinctive fossa, the dorsal cotyla of
the proximal end of the ulna is well preserved, and the metacarpals
are fused at their proximal base, although this area is very
cmshed (Figures 6, 7).
FIM
LRD
LRD
DCT
HAH
RSC
FIGURE 6.—Otogornis genghisi Hou, 1994, from the Chabu Sumu locality,
Ordos Basin, China, Yijinhuoluo Formation. Cranial view; drawing made from
a slide. CGR=capital groove, CRP=cranial pit, DCD=dorsal condyle,
DCR=deltopectoral crest, DCT=dorsal cotyla, FIM=feather imprints, HAH=
humeral articular head, LCR=left coracoid, LFU=ligamental furrow, LHM=
left humerus, LRD=left radius, LUL=left ulna, OL=olecranon, OLF=
olecranal fossa, RHM=right humerus, RRD=right radius, RSC=right scapula,
SGR=scapular groove, TRF=tricipital fossa, VCD=ventral condyle. VTB=
ventral tubercle. (Scale bar=l cm.)
A wide, flat humeral articular facet in the scapula of Otogornis
faces latero-cranially. The projecting ventral edge of the
proximal end of the humerus in Otogornis possesses a small
cranial tubercle with a pit in the center that is very similar to
Ambiortus. Perhaps Otogornis is similar to Ambiortus and the
Lifhornifhiformes in the specialized morphology of having a
dorsoventrally compressed scapular acromion with a tubercle
on its dorsal side. Despite being broken, the acromion of
Otogornis shows some dorsoventral flattening with a prominence
on the dorsal surface. The cranial portion of the lateral
surface of the scapula bears a distinctive scapular groove.
The specimen of Otogornis genghisi exhibits the imprints of
two wing feathers. Hou (1994) pointed out an important characteristic
of these feathers, which is that they are not tightly arranged,
i.e., there is no bonding of the barbs by barbules. Ambiortus
dementjevi also preserves some feather imprints in the
area of the wing feathers, although these show bonded feather
vanes.
COMPARISON
The bones of the shoulder girdle and forelimb in Otogornis
genghisi are somewhat longer than those in Ambiortus de-