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210
siderably more sternally than does the angulus medialis (Figure
3A,B,F).
All three known genera of the Jungornithidae are clearly distinguished
from other fossil and modern Apodiformes by the
presence of a well-developed proc. lateralis in the sternal part
of the coracoid (Figure 3).
In caudal aspect, the overall configuration of the caput humeri
in Argornis is most similar to that in Hemiprocne: the
smaller ventral part of the head is placed approximately perpendicular
to the long axis of the bone, whereas its greater part
is placed obliquely and more distally relative to the ventral part
of the head. At the same time, Argornis differs from Hemiprocne
in having the caput humeri directed mainly caudally, in contrast
to Hemiprocne in which it is directed apically. Both Argornis
and Jungornis have a relatively distally placed proc.
supracondylaris dorsalis, similar to that in Aegialomis. In comparison
with other Apodiformes, Argornis possesses the most
distally situated tuberculum supracondylare ventrale, revealing
a tendency toward the proximal displacement found in all
apodiform families.
In Argornis and Jungornis the cotyla ventralis ulnae has a
slightly pronounced ventroproximal edge. The Trochilidae possess
a similar structure of the cotyla ventralis in this regard,
whereas in the Hemiprocnidae and Apodidae its ventroproximal
edge is well marked.
Argornis caucasicus, new species
FIGURES 1,2A-P, 3C
HOLOTYPE.—Incomplete, partially crushed articulated skeleton
including the vertebral column, shoulder girdle, and forelimbs;
Paleontological Institute of the Russian Academy of
Sciences, PIN 4425-18.
TYPE LOCALITY.—Gorny Luch, left bank of Pshekha River,
northern Caucasus, Russia.
HORIZON.—Kuma (Kumsky) horizon, upper Eocene (Bannikov,
1993).
MEASUREMENTS (in mm).—Clavicle, minimum width 0.5,
maximum width 0.9; scapula, dorsoventral width of cranial end
2.4; coracoid, length 10.0, diameter of midshaft 0.9 by 1.0, mediolateral
width of sternal end 2.6, dorsoventral width of sternal
end 1.2, distance between tips of angulus medialis and angulus
lateralis 1.8; humerus, length 10.4, proximal dorsoventral
width 4.1, distal dorsoventral width 3.3; ulna, length 16.0; radius,
length 15.1, diameter of midshaft 0.5 by 0.7; carpometacarpus,
length 11.6, craniocaudal width through extensor process
3.8, craniocaudal width of midshaft of major metacarpal 1.1;
proximal phalanx of major digit, length through articular surfaces
6.4, maximum length 7.2, craniocaudal width at middle
2.4; distal phalanx of major digit, length 6.3; phalanx of minor
digit, length 3.0.
Judging from the length of the coracoid, A. caucasicus may
have been approximately the same overall size as Palescyvus
escampensis, which has a coracoid 10.1 mm long (Harrison,
SMITHSONIAN CONTRIBUTIONS TO PALEOBIOLOGY
1984, table 2), although in A caucasicus the coracoid is somewhat
more slender, suggesting smaller body size. Argornis
caucasicus noticeably exceeds Jungornis tesselatus in all corresponding
measurements.
ETYMOLOGY.—After Caucasus, the geographic area of the
type locality.
DESCRIPTION.—Remains of the vertebral column, sternum,
and ribs are too fragmentary and badly damaged for description
of their features.
Clavicula: The scapus claviculae is flattened mediolaterally
and smoothly widened toward the extremitas omalis. The
transition between the clavicular shaft and the proc. acromialis
is not pronounced. The proc. acrocoracoideus protrudes strongly
laterad, its base approximately one-half the dorsoventral
width of the clavicular shaft. The facies articularis acrocoracoideus
is flattened dorsoventrally and is concave mediolaterally.
Scapula: The acromion protrudes a little beyond the level
of the cranial border of the tuberculum coracoideum. The dorsal
margin of the acromial tip is curved laterad, with the crista
lig. acrocoraco-acromiale short craniocaudally. The tuberculum
coracoideum passes gradually into the proc. glenoidalis.
The dorsocaudal part of the proc. glenoidalis protrudes strongly
laterad. The facies articularis humeralis is widened ventrocaudad,
being directed cranioventrally and turned slightly laterally.
Coracoid: The facies articularis clavicularis is convex. The
well-marked cotyla scapularis is rounded and moderately concave.
The proc. procoracoideus is long, its base stretches
caudad almost to the level of the cranial border of the impressio
M. sternocoracoidei. The foramen supracoracoidei, situated in
the middle of the base of the procoracoid, opens ventrally into
a groove that extends along the base. The sulcus supracoracoideus
is well developed craniad of the level of the foramen supracoracoidei.
The impression of M. supracoracoidei is deep
and sharply outlined. The proc. lateralis is obtuse-angled in
frontal aspect. The facies articularis sternalis is subdivided
asymmetrically into a smaller medial and a larger lateral part
by a saddle-like ridge that extends lateroventrad from the angulus
medialis. The larger lateral part is concave in both mediolateral
and dorsoventral dimensions.
Humerus: The tuberculum dorsale is displaced distad from
the dorsal part of the caput humeri. The crista deltopectoralis is
high and tapering, with a concave proximal edge. The tip of the
crista deltopectoralis is approximately on the level of the middle
of the impression of the tendon of M. supracoracoideus.
The proc. supracondylaris dorsalis occurs about one-quarter of
the length of the humerus from its distal end. The tuberculum
M. pronator superficialis is placed approximately on the level
of the tuberculum M. tensor propatagialis pars brevis. The sulcus
intercondylaris is narrow and shallow. The proc. flexorius
is blunt and widened dorsoventrally. The cranial surfaces of the
tuberculum supracondylare ventrale and epicondylus ventralis
are fused continuously, as are the cranial surfaces of the epicondylus
ventralis and proc. flexorius. The fossa of M. brachia-