A revision of atavisms in vertebrates

Abstract

This work deals on a synthesis of the atavisms, on its three main kinds: spontaneous, experimental and taxic, and the basics criteria to recognize them. Many cases on several vertebrates groups are presented: experimental atavisms in the formation of extra-digits in caviomorph rodents and complete fibulae in Aves, and the induction of avian oral epithelium combined with rodent mesenchyme to form teeth; spontaneous atavisms like the occurrence of complete hindlimb in cetaceans and snakes, the extra-digits in horses, the occurrence of mandibular molars in felids and hip muscles in passerine birds; taxic atavisms are discussed in the light of robust phylogenies to each group in question (cichlid fishes, passeriformes birds, pinniped phocids, fossil snakes and gavialine crocodilians) and regarded as a natural consequence of the incorporation of spontaneous atavisms to the taxa. The irreversibility of evolution, or Dollo’s law, arises as an important and underlying theoretical issue, allowing a critical revision about the role of the atavisms in the vertebrate evolution. The importance of genic regulation mechanisms, as the function of Hox genes, the atavisms being useful in searching criteria to establish homologies, and their possible relationship to macroevolutive phenomena are presented, as well as the criticism is analyzed and discussed too.

Key words: vertebrates, experimental atavisms, spontaneous atavisms, taxic atavisms, irreversibility of evolution.