Myology of the Pectoral Appendage in Kingbirds (Tyrannus) and Their Allies

Abstract

-The forelimb muscles of several species of the group are here described and illustrated, with the goal of discovering character states of use in delineating clades within the Tyrannidae. These muscles conform in all species to the oscine pattern as described by other authors, with the exception of a few features. Special attention is given to M. latissimus dorsi caudalis, the only muscle that varies widely among, as well as within, the species examined. Absence of this' muscle in the species ofMyiozetetes could mean that this group is a clade. Variation in other tyrannids, however, indicates that closely related species may be losing M. latissimus dorsi caudalis independently. The present study of wing muscles in the kingbird assemblage (Traylor 1977) was undertaken as part of a larger study, to determine whether the appendicular musculature of New World flycatchers (Tyrannidae) can provide information of use in constructing phylogenetic hypotheses for this group. Anatomical data from the work of Garrod (1876), Ames (1971), MidtgArd (1982), and W. E. Lanyon (pers. comm.) have recently been used in a cladistic analysis of relationships within the Tyrannoidea (McKitrick 1985). Other anatomical data for this group are scarce and incomplete, and much additional information is needed from a variety of anatomical (and molecular) systems to clarify relationships within this group. A few published studies of the forelimb muscles of oscines exist, e.g., Swinebroad (1954), Hudson and Lanzillotti (1955), George and Berger (1966), Borecky (1977), and Raikow (1977, 1978), but I have found virtually no such information for suboscines. I undertook to describe and illustrate the forelimb muscles of several species of the group, and compare them with what is known of these muscles in other passerine birds. My purpose was to determine polarities of character states, and thereby assess the potential of this anatomical system for phylogenetic analysis. Similar data for the hindlimb muscles are provided in McKitrick (in press). My working hypothesis was that the Tyrannidae is monophyletic (McKitrick 1985) and, further, that the group is also a clade (Lanyon 1984). MATERIALS AND METHODS I dissected fluid-preserved specimens of the following species: Tropical Kingbird (Tyrannus melancholicus USNM 504538 and 504539), Rusty-margined Flycatcher (Myiozetetes cayanensis USNM 504542), Piratic Flyca cher (Legatus leucophaius USNM 510867), and Variegated Flycatcher (Empiono us varius FMNH 288494), all members of the group. One muscle, M. latissimus dorsi caudalis, was intraspecifically variable, and I examined this muscle in 39 other species of Tyrannidae to assess the extent of variation. Dissections were done under a stereomicroscope at 6 x, 12 x and 25 x, with the use of iodine stain (Bock and Shear 1972) to enhance visibility of muscle fibers. Anatomical nomenclature is from Baumel et al. (1979), and abbreviations are, for the most part, from Zusi and Bentz (1984). Descriptions of muscles refer to Tyrannus melancholicus, and are the same in the other species unless otherwise stated. Comparisons with other passerine species are noted where differences occur. Abbreviations for museums from which specimens were borrowed are as follows: AMNH, American Museum of Natural History; CM, Carnegie Museum of Natural History; FMNH, Field Museum of Natural History; KU, University of Kansas; LSU, Louisiana State University; USNM, National Museum of Natural History; YPM, Peabody Museum, Yale University. Collection data were reported in McKitrick (1984). RESULTS AND COMPARISONS M. rhomboideus superficialis (Fig. I:RS) is a thin, flat, essentially parallel-fibered muscle, lying deep to M. latissimus dorsi pars cranialis and superficial to M. rhomboideus profundus. It arises by an aponeurosis from the neural spines of the last two cervical vertebrae and the neural spines of the first dorsal vertebrae. It passes craniolaterally to insert by a narrow aponeurosis on the dorsomedial surface of the c anial two-thirds of the scapula. The cranialmost fibers insert at the very cranial tip of the