The Phylogenetic Distribution and Innervation of Craniate Mechanoreceptive Lateral Lines

Phylogenetic studies can be undertaken with a number of aims: (1) to describe the history of traits; (2) to discern form-function relationships that may not be evident from examining the traits in a single species; (3) to generate hypotheses regarding the evolutionary mechanisms responsible for the history of the traits; and (4) to detect gaps in our knowledge of the traits (Gans 1985; Northcutt 1985a, 1986a). The following analysis involves each of these aims but is confined to the distribution and innervation of mechanoreceptive neuromasts. It does not attempt to deal with related receptors and organs or the phylogeny of the octavolateralis system as a whole, although I have discussed electroreceptors and the inner ear in previous publications (Northcutt 1980, 1986a,b).