Overview of Brain Evolution: Lobe-Finned Fish vs. Ray-Finned Fish
Résumé
Bony jawed vertebrates (Osteichthyes) are divided into two groups, ray-finned fish (Actinopterygii) and lobe-finned fish (Sarcopterygii). The tetrapod (including mammals and birds) is a group of lobe-finned “fish” specialized in terrestrial life. Although the overall brain organization is conserved, significant differences exist within each brain region between Actinopterygii and Sarcopterygii. This chapter introduces a new view of the vertebrate brain organization; more particularly, we propose revised subdivisions in the anterior forebrain, which was revealed through comparative analyses between Actinopterygii and Sarcopterygii.
Behaviorally, some teleosts (a group of Actinopterygii) demonstrate higher order cognitive functions such as tool use or transitive inference. Moreover the “fish brains” are not necessarily simpler than tetrapod brains, and some teleost species have an enlarged pallium (dorsal telencephalon) as it is the case in amniotes. Nonetheless, the anatomical organization of the teleost brain is very different from that of the tetrapods, and there are many inconsistencies when we consider that these functional similarities are inherited from the common ancestor. It is possible that the nervous system is highly plastic during evolution, and more convergent evolution has taken place than is currently thought.