A PHYLETIC STUDY OF THE LAKE TANGANYIKA CICHLID GENERA ASPROTILAPIA, ECTODUS, LESTRADEA, CUNNINGTONIA, OPHTHALMOCHROMIS, AND OPHTHALMOTILAPIA KAREL F. LIEM' CONTENTS Abstract 191 Introduction 191 Materials and Methods 192 Osteological Aspects of Ectodus 193 Myological Aspects of Ectodus 195 Comparative Osteology 197 Comparative Myology 203 Phyletic Analysis 205 Acknowledgments 212 Abbreviations 212 Literature Cited 213 Abstract. On the basis of comparative osteology and myology, Asprotilapia, Ectodus, Lestradea, Cunningtonia, Ophthalmochromis, and Ophthal-motilapia of Lake Tanganyika are hypothesized to be members of a monophyletic lineage of cichlid fishes. All members share the following suite of characters: (1) the entopterygoid is widely separat-ed from the palatine; (2) the posterior and dorsal margins of the palatine form a 90° angle; (3) the slender hyomandibula has a long symplectic pro-cess and a very reduced hyomandibular flange; (4) the anterior margin of the pterosphenoid is notched; (5) the vertical depth of the metapterygoid is shallow; (6) the operculum has a distinct auricular process; (7) the transversus dorsalis muscle is re-duced; and (8) the obliquus posterior muscle is en-larged. These characters are considered specialized when compared with the accepted generalized mori^hology oi Astatotilapia. The phyletic relation-ships of this lineage are documented by synapo-morphies that distinguish subunits of decreasing levels of universality within the assemblage. As-protilapia represents a highly specialized branch with six major skeletomuscular specializations. The remaining five genera are pictured as a second lin-' Museum of Comparative Zoology, Harvard Uni-versity, Cambridge, Massachusetts 02138. eage, of which Ectodus is the most generalized tax-on. On the basis of recency of common descent, Ophthalmochromis is synonymized with the genus Ophthalmotilapia. Although there is no doubt that the Ophthalmotilapia lineage has undergone ex-tensive morphological radiation in both skull struc-ture and dentition, the data on morphology, func-tion, trophic ecology, and behavior of this and other cichlid lineages have failed to establish unequivo-cally that the morphological radiation is also adap-tive. The morphological and functional pattern in this lineage reinforces the paradox that morpholog-ically and phylogenetically most specialized cichlid taxa are not only remarkable specialists but also jacks-of-all-trades. INTRODUCTION The precise phylogenetic interrela-tionships of the endemic cichHds in Lake Tanganyika are still unknown (e.g., Fryer and lies, 1972: 507). Essentially the problem is to distinguish groups that are true, hierarchically evolved sister groups showing increasing specialization or apo-morphy, from groups that are gradal as-semblages of polyphyletic ancestry (Greenwood, 1974, 1979). Liem and Stewart (1976) have shown that the lepi-dophagous cichlids of Lake Tanganyika represent a monophyletic lineage. Re-cently Liem (1979) has postulated that because of the basic homogeneity in spe-cialized morphology and function, the in-vertebrate picking cichlids of Lake Tan-ganyika must have originated from a common ancestor. Greenwood (1979) has synonymized Limnotilapia with Simo-Bull. Mus. Comp. Zool., 149(3): 191-214, Februar>-, 1981
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