The protractor pectoralis muscle and the classification of teleost fishes Peter Humphry Greenwood Department of Zoology, British Museum (Natural History), Cromwell Road, London SW7 5BD George V. Lauder 1 Museum of Comparative Zoology, Harvard University, Cambridge, Massachusetts, 02 1 38 Introduction The protractor pectoralis muscle is currently thought to be one of the shared derived features characterizing certain neoteleostean fishes. Further investigation shows, however, that a protractor pectoralis muscle occurs in many taxa throughout the Teleostei, the Dipnoi, the Palaeopterygii and other lower actinopterygians, and, probably, in the Elasmobranchio-morphi as well. Since the protractor pectoralis is apparently homologous with the trapezius muscle of tetrapods it therefore would appear to be a derived feature of the Gnathostomata as a whole and not just a synapomorphy of a group (the Eurypterygii) within the Teleostei. In his paper on the interrelationships of the higher Euteleostei, Rosen (1973) considered the presence of a protractor pectoralis muscle to be one of the synapomorphies characterizing the section Eurypterygii of his subdivision Neoteleostei. Rosen also included in the Neoteleostei, as the primitive sister group of the Eurypterygii, the section Stenopterygii (=Stomiatiformes). Although lacking a protractor pectoralis muscle, the Stomiatiformes share other derived features with their apomorph sister taxa, viz. the Aulopiformes, Myctophiformes, Protacanthopterygii and Acanthopterygii (Rosen, 1973:505). According to Rosen (who based his conclusions involving the protractor pectoralis largely on the then unpublished work of Winterbottom) this muscle does not occur in any other group of teleostean fishes. When that work was published the following year, Winterbottom (1974 : 269) repeated the claim that '. . . the protractor pectoralis appears to be confined to the neoteleosts', despite the fact that he described and illustrated the muscle in three non-neoteleostean taxa, the ostariophysans Brycon, Cyprinus and Diplomystus. This lapsus is probably explained by Winterbottom's definition of the concepts 'neoteleosts' and 'non-neoteleosts' (Winterbottom, 1974 : 227). He uses the term neoteleost *. . . in the sense proposed by Rosen & Patterson (1969 : 460)' but uses its antithesis, the non-neoteleosts, '. . . to designate Divisions I and II, and the salmoniforms (less mycto-phoids) of Division III of the Greenwood et al. (1966) classification'. Thus the Ostariophysi and the Gonorynchiformes of Greenwood et al. were left in limbo, neither neoteleosts nor non-neoteleosts, and were overlooked. A further complication is introduced by Winterbottom's report in some clupeomorphs (sensu Greenwood, Rosen, Weitzman & Myers, 1966) of a muscle which, in his opinion (1974 : 269) '. . . seems to be analogous to the protractor pectoralis', and with which '. . . the muscle in the neoteleosts would appear to be a homologous structure, and indicative of common ancestry'. These incongruities in recently published accounts, coupled with the fact that a muscle apparently identical to the protractor pectoralis in neoteleosts has been described in 'Present address: Department of Anatomy, University of Chicago, 1025 East 57th Street, Chicago, Illinois 60637, USA Bull. Br. Mus. nat. Hist. (Zool.) 41(4): 2 1 3-234 Issued 26 November 1 98 1
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