Pleuronectiform Relationships: A Cladistic Reassessment

Flatfish monophyly, interrelationships and intrarelationships are examined. The order Pleuronectiformes is monophyletic on the basis of three synapomorphies: cranial asymmetry associated with ocular migration, advanced position of the dorsal fin over the cranium and presence of a recessus orbitalis. Characters used to postulate a relationship between percoids and flatfishes are found to be plesiomorphic and the sister group of flatfishes remains unknown. The monophyletic status of all suprageneric taxa of Pleuronectiformes is reexamined and a cladistic analysis is performed using a character state matrix of 39 polarized morphological (mainly osteological) characters. Eighteen equally parsimonious trees were generated. A consensus tree was constructed and discussed in detail. It is concluded that phylogenetic knowledge within flatfishes remains very incomplete. The monophyletic status of speciose taxa such as the Pleuronectinae and Paralichthyidae will have to be reassessed before any fruitful statement of relationships can be formulated.