Caecilian viviparity and amniote origins

Abstract

A recent evaluation of alternative hypotheses for the origin of the amniotic egg, by mapping a single reproductive-mode character onto a phylogeny of tetrapods, concluded that the alternative hypotheses were equally parsimonious. However, this interpretation is dependent upon a mistaken coding of the caecilian amphibians as showing extended embryo retention. Although some caecilians are viviparous, phylogenetic analyses indicate that oviparity is ancestral for the group. With the coding of caecilians corrected, the most parsimonious inference is that the ancestral amniotes did not practice extended embryo retention. A review of the available data indicates that the widespread view that a majority of caecilians are viviparous is mistaken. Oviparity is the dominant reproductive mode in caecilians as it is in other living amphibians.

Keywords :

• Evolution
• phylogeny
• parsimony
• Amniota
• Gymnophiona
• reproductive modes