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A New Genus and Species
of the Family Jungornithidae (Apodiformes) from the
Late Eocene of the Northern Caucasus,
with Comments on the Ancestry of Hummingbirds
ABSTRACT
Argornis caucasicus, a new genus and species of the family
Jungornithidae (Apodiformes), is based on an incomplete, articulated
skeleton of the shoulder girdle and wing from the late Eocene
of the northern Caucasus. The holotype includes the manus, which
was previously unknown in the Jungornithidae. In comparison
with early Oligocene Jungornis, the new form is less advanced
evolutionarily, and, in particular, it lacks certain characters shared
by Jungornis and the Trochilidae. An emended diagnosis of the
family Jungornithidae is given. Taking into account that both Jungornis
and Argornis possess an apodid-like deltopectoral crest,
revealing their highly developed ability for gliding flight, the
appearance of trochilid-like features in Jungornis demonstrates a
real possibility that hovering specializations developed from gliding
adaptations. This conclusion conforms with the results of a
comparative analysis of the transformation of forelimb muscles in
three modem apodiform families.
Introduction
Jungornis tesselatus Karhu, 1988, a bizarre Paleogene apodiform
referred to its own family, was described from an incomplete,
articulated skeleton of the shoulder girdle and forelimb
from the early Oligocene of the northern Caucasus. The second
genus and species of the family Jungornithidae described,
Palescyvus escampensis Karhu, 1988, was based on a single
coracoid from the late Eocene of the Phosphorites du Quercy,
France, that Mourer-Chauvire (1978) had previously assigned
to Cypselavus gallicus Gaillard.
Alexandr A. Karhu, Paleontological Institute, Russian Academy of
Sciences, Profsoyuznaya Street 123, Moscow, 117868, Russia.
Alexandr A. Karhu
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The Jungornithidae possess features in common with such
evolutionarily advanced families as the Apodidae and Trochilidae;
the Jungornithidae also demonstrate a clear resemblance
to the comparatively generalized apodiform family Hemiprocnidae,
and even to the Caprimulgidae. An unusual combination
of characters in the Jungornithidae, some of which are shared
separately either with the Apodidae or with the Trochilidae, has
been considered evidence in favor of the common origin of
these three families (Karhu, 1988, 1992a, 1992b). Further investigation
of the apodiform flight apparatus has revealed, in
particular, that an important part of the morphofunctional specializations
in hummingbirds represents subsequent stages of
development from the apodid-like adaptations (Karhu, 1992a).
This contradicts the principal conclusion of Cohn (1968) that
the similarity between the true swifts and hummingbirds is the
result of convergence.
In 1993, a new genus and species of jungornithid, described
herein, was found in a late Eocene locality, Gorny Luch, northern
Caucasus, that has yielded an abundant marine ichthyofauna
(Bannikov, 1993). This discovery provides important data
concerning the morphological specialization of the flight apparatus
in the Jungornithidae. Taking into account the essential
similarities between the Jungornithidae and Trochilidae, an
older example of the former family may shed light on the early
evolution of hummingbirds.
METHODS.—Comparative study of the forelimb muscles in
modern Apodiformes is very important for analysis of evolutionary
trends. The forelimb muscles of the following species
were studied (number of specimens is in parentheses): Hemiprocnidae:
Hemiprocne mystacea (1), Hemiprocne comata (1);
Apodidae: Collocalia lowi (1), Hirundapus caudacutus (1),
Chaetura pelagica (1), Chaetura brachyura (1), Apus apus (4),
Apus pacificus (1); Trochilidae: Chlorostilbon ricordii (1),
Chlorostilbon sp. (1), Heliomaster longirostris (1), and Papho-