Phylogeny of early tertiary swifts and hummingbirds (Aves: Apodiformes)

Auk, The, Jan 2003 by Mayr, Gerald

The nectarivorous hummingbirds evolved a derived mode of hovering flight that allows them to remain virtually motionless in front of flowers. Probably as an adaptation to their unique way of locomotion, extant Trochilidae have unusually short wings (Rayner 1988) that differ from the long and pointed wings of swifts.

The feathering of either Argornis or Jungornis is unknown, but there is a specimen (Fig. 4) of an apodiform bird from the Middle Eocene of Messel, Germany, which is osteologically very similar to Argornis and in which the wing and tail feathers are excellently preserved (Mayr 2003). As in Argornis, the robust humerus is strongly abbreviated and bears a poorly developed processus musculi extensor metacarpi radialis which is much more protruding in other apodiform taxa with a similarly abbreviated humerus (i.e. Jungornis, extant Trochilidae, and the Apodidae; see Fig. 3). The Messel apodiform further exhibits the diagnostic characters that support monophyly of the taxon (Argornis [Jungornis extant Trochilidae]) (see Fig. 1). Most unusual and completely unexpected is the combination of a short and stout humerus with a short and broad wing, the tip of which is completely preserved in the specimen. If it is a stem group representative of the Trochilidae, the Messel apodiform might indicate that strongly elongated wings indeed are synapomorphic for the taxon (Hemiprocnidae Apodidae) and that the Trochilidae evolved from a rather short-winged ancestor.

It has been assumed that hummingbirds evolved from insectivorous ancestors (e.g. Cohn 1968) and underlying the phylogeny in Figure 1, a "swift-like" or "aegothelid" beak almost certainly was present in the last common ancestor of the Apodiformes and is thus plesiomorphic for the taxon (Jungornis Trochilidae). Hovering ability of hummingbirds might have primarily evolved as an adaptation for gleaning insects from the underside of leaves (Cohn 1968) or around flowers and was a preadaptation for the highly derived nectarivory of extant Trochilidae (Mayr and Manegold 2002).

ACKNOWLEDGMENTS

I thank S. Chapman (The Natural History Museum, London) for access to fossil specimens and R. Prum, K. Smith, R. Zusi, and two anonymous reviewers for comments on the manuscript. S. Trankner (Forschungsinstitut Senckenberg) took the photograph.

LITERATURE CITED

BALLMANN, P. 1976. Fossile Vogel aus dem Neogen der Halbinsel Gargano (Italien), zweiter Teil. Scripta Geologica 38:1-59.

BAUMEL, J. J., AND L. M. WITMER. 1993. Osteologia. Pages 45-132 in Handbook of Avian Anatomy: Nomina Anatomica Avium (J. J. Baumel, A. S. King, J. E. Breazile, H. E. Evans, and J. C. Vanden Berge, Eds.). Publications of the Nuttall Ornithological Club, no. 23.

COHN, J. M. W. 1968. The convergent flight mechanism of swifts (Apodi) and hummingbirds (Trochili) (Aves). Ph.D. dissertation, University of Michigan, Ann Arbor.

COLLINS, C. T. 1976a. A review of the Lower Miocene swifts (Aves: Apodiformes). Pages 129-132 in Collected Papers in Avian Paleontology Honoring the 90th Birthday of Alexander Wetmore (S. L. Olson, Ed.). Smithsonian Contributions to Paleobiology, no. 27.