Evidence for a Polyphyletic Origin of the Piciformes

-Despite two recent anatomical studies to the contrary, the order Piciformes appears to be polyphyletic. The structure of the zygodactyl foot in the Galbulae is very distinct from that in the Pici, and no unique shared derived characters of the tarsometatarsus have been demonstrated for these two taxa. The supposedly three-headed origin of M. flexor hallucis longus shared by the Galbulae and Pici is doubtfully homologous between the two groups, leaving only the Type VI deep flexor tendons as defining the order Piciformes. This condition is probably a convergent similarity. Evidence is presented supporting a close relationship between the Galbulae and the suborder Coracii and between the Pici and the Passeriformes. There are fewer character conflicts with this hypothesis than with the hypothesis that the Piciformes are monophyletic. Problems concerning fossil taxa are also addressed. Received 24 September 1981, accepted 15 May 1982. A MONOPHYLETIC origin of the Piciformes appears to have gained support from the simultaneous appearance of two cladistic, anatomical papers (Swierczewski and Raikow 1981, Simpson and Cracraft 1981) that concur in the traditional concept of the order-a concept that has prevailed at least since the time of Gadow (1893). I depart from this view in considering each of the two major subdivisions of the Piciformes, the Galbulae (Bucconidae, Galbulidae) and the Pici (Capitonidae, Ramphastidae, Indicatoridae, Picidae), to be more closely related to another group than to each other. My purpose here is (1) to show that the evidence for monophyly is weak, uncorroborated, and has in part been misrepresented by Simpson and Cracraft (1981), and (2) to make preliminary suggestions as to the probable closest relatives of the Galbulae and the Pici. THE WEAKNESS OF THE EVIDENCE FOR PICIFORM MONOPHYLY Zygodactyly.-Obligate zygodactyly, the condition in which the fourth toe is permanently reversed and has an enlarged accessory articulating process (the "sehnenhalter"), occurs in cuckoos (Cuculidae, Cuculiformes), parrots (Psittacidae, Psittaciformes), and in the Piciformes. This is obviously a derived condition in birds that could be used to define these taxa as a monophyletic group in a cladistic sense, unless it were shown that each of these zygodactyl taxa shares derived characters with outside groups in a manner indicating that the zygodactyl condition in cuckoos, parrots, and Piciformes had arisen independently, through convergence. Although I certainly do not advocate a monophyletic origin of zygodactyl birds, the arguments that Simpson and Cracraft (1981) and Swierczewski and Raikow (1981) present against such a hypothesis do not meet the requirements of their cladistic methodology. Simpson and Cracraft (1981: 484) conclude only that "the relationships of cuckoos and parrots remain among the most enigmatic within ornithology ," although "there is a general acceptance among avian systematists . . . that piciforms are most closely related to coraciiforms or to passeriforms and that cuckoos and parrots are not." They concede that "this hypothesis has yet to be tested cladistically ....' Swierczewski and Raikow (1981: 469) state that: "The muscular component of the foot mechanism is quite different in [the Cuculidae, Psittacidae, and Piciformes] . . . which supports the contention (Bock and Miller 1959: 30) that those groups became zygodactyl independently." Both sets of authors have thus tacitly accepted differences between taxa as evidence of nonrelationship, a procedure of which Cracraft has been outspokenly critical (see Olson 1982). The most complete and original work on the nature of the zygodactyl foot is that of Steinbacher (1935), whose results have seldom been accurately represented (a notable exception being Sibley and Ahlquist 1972). Steinbacher 126 The Auk 100: 126-133. January 1983 This content downloaded from 157.55.39.104 on Sun, 19 Jun 2016 05:50:06 UTC All use subject to http://about.jstor.org/terms January 1983] Polyphyletic Origin of the Piciformes 127