A Model for the Evolution of Perching Birds

Feduccia, A. (Department of Zoology, University of North Carolina, Chapel Hill, North Carolina 27514) 1976. A model for the evolution of perching birds. Syst. Zool. 26:19-31.The Passeriformes and related avian orders (here termed "perching birds") have presented almost insurmountable problems in resolving phylogenetic relationships. New evidence from the morphology of the avian stapes (columella) permits a reassessment of the phylogenetic relationships of the advanced perching birds. Though the stapes represents but a single character, the primitive condition for the element can be established beyond reasonable doubt as that condition found in the reptilian ancestors of birds and present in the vast majority of living birds. Therefore, where unique, derived morphologies of the stapes occur, they may be of great importance in establishing evolutionary relationships within these groups, as no other characters are presently available for which primitivederived sequences can be established beyond doubt. A cladistic approach to stapedial morphology permits a number of probable evolutionary statements concerning the "perching birds" as follows: 1) New and Old World suboscines are a monophyletic assemblage, and this group, now termed the Tyranniformes, includes the previously classified subocines of Madagascar, but not those of Australia (the lyrebirds and allies, and the New Zealand Wrens), which are shown to be oscines; 2) the wood-hoopoes and hoopoes are monophyletic and possess a unique "anvil" stapes; 3) the bee-eaters, motmots, kingfishers, and todies possess a common derived stapedial morphology and almost certainly represent a monophyletic assemblage; 4) trogons possess a stapedial morphology identical to that of the above assemblage (in 3) and are probably derived from that particular group, all of which are now termed the Alcediniformes; 5) the oscines and suboscines could not have shared a common ancestor because suboscines show a myriad 6f primitive characters with respect to the oscines, are relictually distributed, and yet possess a derived stapedial morphology, while the otherwise structurally advanced oscines possess the primitive condition of the stapes; for that reason the order Passeriformes is restricted to include only the oscines; 6) the Tyranniformes (suboscines) and Alcediniformes may have shared a common ancestor; both groups possess derived morphologies of the stapes that share many common features, but establishing beyond all doubt that the morphologies are strictly homologous is difficult. New evidence from the fossil record (particularly from the Western Hemisphere) provides a new basis for a paleobiogeographic analysis of "perching birds. " This new evidence indicates that: 1) The Eocene of North America was a period during which structurally primitive piciform birds were the predominant, if not the only, perching birds. Eight species -are now known from the Lower and Middle Eocene of North America, including one previously thought to represent a passerine. 2) The piciforms are probably New World in origin, and could have dispersed into the Old World via Beringia or across the North Atlantic. 3) The alcediniform birds are almost certainly Old World in origin; trogons, motmots, and perhaps todies crossed over into the New World using the Beringia route; alcediniforms were probably predominant during the Oligocene. 4) Suboscines are probably a Southern Continent group, and probably did not arrive into North America until relatively late, perhaps late Pliocene or early Pleistocene, when a Central American land bridge became established. 5) The Bering route probably served as a corridor for the arrival of oscines in the New World that gave rise to the New World nine-primaried oscine radiations. Apparently North America did not reciprocate to any significant degree. Oscines probably did not become established firmly in North America until the Miocene and are late arrivals into Central and South America; they probably entered these regions as late as late Pliocene or early Pleistocene when the Central American land bridge became established. [Phylogenetic relationships; "perching birds"; Passeriformes; stapes; paleobiogeography. ] As a morphologically uniform group of 1 Plenary lecture presented at the ninety-third meeting of the American Ornithologists' Union in Winnipeg, Manitoba, August, 1975. vertebrates, birds present more problems in resolving phylogenetic relationships than any other group of tetrapods (Bock, 1963). The major difficulties are due to such fac-