Evolution and taxonomy of the Silurian conodont Pterospathodus

New data indicate that Carniodus is not a separate taxon but the elements considered to belong to it in reality formed a part of the Pterospathodus apparatus. The latter contains 14 elements: Pa, Pb1, Pb2, PC, M1 (+M2 in P. pennatus procerus), Sc1 Sc2, Sc3, Sb1, Sb2, Sa, carnuliform with five morphs, carniciform, and curved element with three morphs. Two ecologically distinct lineages existed and evolved separately. One lineage (P. amorphognathoides angulatus - P. amorphognathoides lennarti ssp. nov. - P. a. lithuanicus - P. a. amorphognathoides) dominated open shelf carbonate-terrigeneous environments and the other (P. pennatus pennatus - P. p. procerus) the deeper basinal, graptolite-bearing facies. Both lineages evidently originated from a common ancestral taxon at the top of the P. eopennatus Biozone. Three main evolutionary 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 morphological variation within each population considerably higher, in the P. amorphognathoides lineage. P. a. angulatus and P. p. pennatus are recognized as separate taxa. P. celloni has a short range and originated from the P. pennatus lineage. Five morphologically distinct chronological populations are recognized in the P. a. amorphognathoides range.