EVOLUTION AND TAXONOMY OF THE SILURIAN CONODONT PTEROSPATHODUS

New data indicate that Carniodus is not a separate taxon but the eleme nts considered to belong to it in reality formed a part of the Pterosp athodus apparatus. The latter contains 14 elements: Pa, Pb-1, Pb-2, Pc , M-1 (+ M-2 in P. pennatus procerus), Sc-1, Sc-2, Sc-3, Sb-1, Sb-2, S a, carnuliform with five morphs, carniciform, and curved element with three morphs. Two ecologically distinct lineages existed and evolved s eparately. One lineage (P. amorphognathoides angulatus - P. amorphogna thoides lennarti ssp. nov. - P. a. lithuanicus - P. a. amorphognathoid es) dominated open shelf carbonate-terrigeneous environments and the o ther (P. pennatus pennatus - P. p. procerus) the deeper basinal, grapt olite-bearing facies. Both lineages evidently originated from a common ancestral taxon at the top of the P. eopennatus Biozone. Three main e volutionary intervals, separated by levels at which the most distinct morphological changes to the elements took place, have been recognized in the Pterospathodus sequence. Evolution was more rapid, and the mor phological variation within each population considerably higher, in th e P, amorphognathoides lineage. P. a. angulatus and P. p. pennatus are recognized as separate taxa. P. celloni has a short range and origina ted from the P. pennatus lineage. Five morphologically distinct chrono logical populations are recognized in the P. a. amorphognathoides rang e.