Normal range and variation in the ontogeny of the Late Paleozoic ammonoid family Marathonitidae

Abstract

The ontogeny and phylogeny of members of the Late Paleozoic family Marathonitidae are ana-lyzed. The ontogeny of some taxa shows variation in major morphological characters, including the shell shape and sutural outline. The range of variation of the characters examined is defined, and deviations from the normal range are considered to be instrumental in the derivation of new groups of various taxonomic ranks.