EIFELIAN ICRIODIDS (CONODONTS) FROM THE BRYANSK REGION AND THEIR ONTOGENY

Abstract

The ontogeny of five conodont species of the genus Icriodus, widespread in the Mosolovian and Chernoyarian horizons of the Eifelian of the central part of the Russian Platform, was studied. The extremes of the Icriodus formosus ontogenetic series strongly differ in morphology. The assignment of these forms to the same species is based on our ontogenetic reconstructions. The other four species, i.e., I. struvei, I. introlevatus, I. platyobliquimarginatus, and I. lindensis, are relatively constant in morphology. The ontogenetic series give evidence for establishing tentative phylogenetic relationships of the species examined. Icriodus formosus is a descendant of I. norfordi; I. struvei and I. introlevatus are descendants of I. corniger; and I. platyobliquimarginatus and I. lindensis are descendants of I. regularicrescens.