Publication Date


Document Type


First Advisor

Jollie, Malcolm

Degree Name

M.S. (Master of Science)

Legacy Department

Department of Biological Sciences


Vertebrae; Catfishes--Anatomy; Fishes--Anatomy; Gymnotidae--Anatomy


Gymnotoid fishes are the wholly electrogenic and Neotropical component of Ostariophysi , a group which constitutes approximately three-fourths of the world's freshwater teleost species. Despite great anatomical diversity, ostariophysans are monophyletic, being characterized by extensive modification of the anterior vertebrae and (especially) the possession of a series of bony ossicles connecting the gas bladder and inner ear, the Weberian apparatus. Literature concerning the anatomy of the anterior vertebral region in gymnotoids, as well as with the phylogenetic relations of this group to other Ostariophysi, is incomplete. This thesis attempts to remedy this situation by providing a detailed description of the anterior vertebral modifications as seen in gymnotoids, and a comparison of their condition to members of other ostariophysan lineages. The fossil history, biogeography and other anatomical features of gymnotoids, characoids and catfishes are considered in a phylogenetic context. Major conclusions resulting from this study are that 1) within Gymnotoidea there exists a clear anatomical distinction between the electric "eel" and knifefishes, and that this justifies taxonomic revision; 2) within the knifefish families there is little patterned variation among anterior vertebral modifications, including the Weberian apparatus, and thus this region is of little taxonomic importance for these families; and 3) characoids are the most probable ancestral source of the relatively recent Gymnotoidea.


Bibliography: pages [43]-47.


viii, 50 pages




Northern Illinois University

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