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NUMBER 89 209
son with other known Apodiformes, and it appears to be closest
to that in the Caprimulgidae.
Scapula: The cranial margin of the acromion is strongly
beveled laterally in Argornis, whereas in Jungornis the margin
is thickened. The crista lig. acrocoraco-acromiale is well developed
in Argornis, but it is not pronounced in Jungornis. In Argornis
the facies articularis humeralis is relatively longer craniocaudally
and wider dorsoventrally in comparison with
Jungornis.
Coracoid: The overall configuration is close to that in Jungornis.
In these genera the shaft is relatively slender, and the
mediolateral width of the processus acrocoracoideus exceeds
the distance between the angulus medialis and the angulus lateralis
of the sternal facet (Figure 3c,D), whereas in Palescyvus
the shaft is stouter, and the acrocoracoid is narrower than the
sternal facet in frontal aspect (Figure 3E). In Argornis the dorsal
crest of the medial portion of the acrocoracoid protrudes
caudally almost to the level of the middle of the dorsal aperture
of the canalis triosseus, and the base of this crest does not reach
laterally to the level of the medial border of the impressio lig.
acrocoracohumerale. In Jungornis the crest projects much less
caudad, and its base is relatively wider, extending laterad to the
level of the medial edge of the impression mentioned above. In
Palescyvus the medial portion of the acrocoracoid curves
strongly caudally but lacks a pronounced dorsal crest. The base
of the proc. procoracoideus is relatively wider in Argornis in
comparison with either Jungornis or Palescyvus. The facies articularis
sternalis is saddle-shaped in Argornis but is concave in
Jungornis. In Argornis only the medial part of the crista ventralis
of the sternal facet protrudes ventrad, whereas in Jungornis
the entire crista ventralis forms a ventral convexity. The ratio
of the greatest dorsoventral width of the sternal facet to the distance
between the angulus medialis and angulus lateralis is
smaller in Argornis than it is in Jungornis. The angulus medialis
is rounded in Argornis and in Palescyvus, whereas in Jungornis
it is moderately sharpened. The angulus lateralis
projects slightly distad beyond the level of the angulus medialis
in Argornis; in Jungornis and Palescyvus the angulus medialis
and angulus lateralis are placed approximately on the same level
(Figure 3C-E).
Humerus: In Argornis the humeral shaft is more slender,
and both the proximal and distal ends are relatively narrower in
comparison with Jungornis (Figure 2E-G,R). The smaller, ventral
part of the caput humeri is situated perpendicularly to the
long axis of the bone in Argornis, unlike in Jungornis, in which
the entire caput humeri is transversely placed (Figure 2H,R).
There is no distal enlargement of the middle of the caput humeri
on the facies caudalis in Argornis as there is in Jungornis.
In Argornis the clearly pronounced tuberculum of M. tensor
propatagialis pars brevis adjoins distally the base of the proc.
supracondylaris dorsalis. This process in Jungornis is adjoined
distally by a high thin crest, and the insertion of M. tensor propatagialis
pars brevis is not marked. Tuberculum M. pronator
superficialis is low and is clearly separated from the tubercu­
lum supracondylare ventrale in Argornis, whereas in Jungornis
the former protrudes strongly proximad and fuses with the
proximal part of the tuberculum supracondylare ventrale. In
Argornis the tuberculum supracondylare ventrale adjoins the
base of the condylus ventralis ventroproximally, but in Jungornis
it is placed more proximally and is well separated from the
base of the condylus ventralis. In Argornis the condylus ventralis
projects distad beyond the condylus dorsalis, whereas the
distal borders of both condyli are placed on the same level in
Jungornis. In Argornis the epicondylus ventralis protrudes
strongly ventrad, is widened proximodistally, and is fused distally
with the proc. flexorius, unlike the much smaller and detached
epicondylus ventralis of Jungornis. The proc. flexorius
projects distad less in Argornis than in Jungornis.
Ulna: In Argornis the tuberculum lig. collaterale ventrale
is smaller and protrudes less ventrad in comparison with Jungornis.
Radius: In contrast to Jungornis, there is an impression of
M. biceps brachii on the ventrocranial surface of the tuberculum
bicipitale brachii in Argornis.
REMARKS.—An extremely peculiar morphology of the sternocoracoidal
articulation is among the most characteristic features
of the Apodiformes sensu Wetmore, 1960 (Lucas, 1893;
Lowe, 1939; Cohn, 1968; Karhu, 1988, 1992a). In the Apodiformes,
the sternum possesses a weakly saddle-shaped or convex
facies articularis coracoidei instead of the coracoidal sulcus
of most birds. Consequently, the coracoid has a more or
less dorsoventrally widened facies articularis sternalis that is
slightly saddle-shaped, or concave, and placed on the whole
perpendicularly to the long axis of the bone. There is a single
exception: in Aegialomis the coracoid has the sternal facet ventrally
widened near the angulus medialis, whereas its greater
part is wedge-shaped in dorsoventral section, as is typical for
most birds.
The structure of the sternal facet of the coracoid is considerably
more generalized in Argornis in comparison with Jungornis.
In Jungornis the overall configuration of the facies articularis
sternalis is apodid-like, with the entire ventral margin
convex ventrad but to a lesser degree than in true swifts. In Argornis
the coracoid possesses a facies articularis sternalis that
is widened by a ventral prominence in its medial part only,
which is similar to the most generalized type within Apodiformes
as demonstrated by Aegialomis. Argornis differs from
Aegialomis, however, in having the dorsal edge of the sternal
facet situated much more sternally (Figure 3A,C).
The other relatively generalized character of the coracoid in
Argornis is the placement of the angulus lateralis slightly beyond
the level of the angulus medialis (Figure 3C). In Jungornis
and Palescyvus the angulus lateralis and angulus medialis
are on the same level relative to the long axis of the bone (Figure
3D,E), which was pointed out as a distinctive familial character
in the former diagnosis of the Jungornithidae (Karhu,
1988). In the Hemiprocnidae and Apodidae, as well as in the
Eocene genus Aegialomis, the angulus lateralis protrudes con-