Some remarks on the ontogenetic development and sexual dimorphism in the Ammonoidea

Abstract

The writer discusses the problem, suggested by some authors, of interpretation of small forms in Ammonoidea as neotenic ones. The classical conception of neoteny is connected with presence of a larval stage which in Ammonoidea was very tiny. It therefore appears that small forms in Ammonoidea are highly advanced in their ontogenetic development as compared with a larval stage of this group. Numerous examples are also known of the dimorphism, the large and small forms in which differ in their dimensions very indistinctly. The latter facts contradict a conception of a neotectonic character of small forms. The writer discusses also the problem of systematics of the Ammonoidea against the background of the commonly being accepted theory of sexual dimorphism.