PDF (Lo-Res) - Smithsonian Institution Libraries

280
The left coracoid is represented by the shoulder end and
shaft. The sternal end is covered by matrix and sternal bone,
but it is well seen in the x-radiograph (Figure 5). The sternal
end is wide and flat, with a long-pointed medial angle and with
a rectangular lateral process. Such a structure of the medial angle
is very similar to that in Lithornisplebius Houde, 1988. The
acrocoracoid is sturdy, relatively short, and its dorsal top is
three-edged and bluntly acute. The craniomedial side of the acrocoracoid
bears an elongate depression that probably represents
an articulation for the clavicle. The lateral side of the acrocoracoid
possesses a wide, slightly concave depression of the
acrocoracohumeral tendon. Ventral to this depression, a relatively
small humeral articular facet is located, the facet being
exposed laterally. An ellipsoidal scapular cotyla is exposed
caudolaterally and is located on an enlarged base of a wide,
flat, long procoracoid process. The sternal portion of the coracoidal
shaft is strongly broadened. None of the elements of the
shoulder girdle are compressed, and they all preserve the tme
configurations of the bones.
WING BONES.—The proximal end of the left humerus was
strongly compressed in its plane during preservation. The humeral
articular head is small, bean-shaped, and located in the
ventral position of the proximal end. The humerus has a
well-developed deltopectoral crest beginning very close to the
humeral articular head in the most proximal position of the
proximal end; it is similar to that in Lithornis plebius. The deltopectoral
crest is flat but is rather deflected dorsally, contrary
to Elzanowski (1995), who described it as projecting laterally.
FIGURE 4.—Shoulder articulation in Ambiortus dementjevi on the opposite
view of the main slab, PIN 3790-271+. ACR=acromion, APR=acrocoracoid
process, ATB=acromial dorsal tubercle, CMR=caudal margin, DPT=dorsal
pit, HAH=humeral artiular head, TRF=tricipital fossa, VTB=ventral tubercle.
(Scale bar= 1 cm.)
SMITHSONIAN CONTRIBUTIONS TO PALEOBIOLOGY
FIGURE 5.—X-radiograph of the main slab with Ambiortus dementjevi. The
sternal end of the coracoid with the medial angle and structure of the vertebrae
can be clearly seen. CTP=caudal transverse process, LPC=lateral process of
coracoid, MAN=medial angle of stemal end of coracoid, RB=rib, V10=10th
vertebra.
Along the dorsal margin, a shallow groove appears in the proximal
half on the cranial side. The bicipital crest and pneumotricipital
fossa are absent; the latter is expressed only as a tricipital
depression (Figure 4). The ventral edge of the proximal end
of the humerus is remarkably projected ventrally. Its distal
edge is like a boss. The cranial surface of this boss possesses a
slightly pronounced cranial tubercle with a pit in the center.
Cranially from this tubercle is a noticeable ligamental fossa
(not a groove). Lithornis plebius also has a similar tubercle
possessing a pit and has a ligamental fossa instead of a furrow.
Such a ligamental fossa is probably the homolog of the transverse
ligamental furrow. On the caudal surface of the proximal
end, a small dorsal pit is developed in the usual place of the
dorsal tubercle. A small ventral tubercle is represented on the
caudal surface of a projecting ventral edge. The capital groove
is not developed. A slightly elevated caudal margin mns along
the middle of the shaft and is directed toward the middle of the
humeral head.
The ulna is badly damaged. Only its distal end and a mold of
a portion of the shaft are preserved on the main and associated