Glyptopomus bystrowi (Gross, 1941), an “osteolepidid” tetrapodomorph from the Upper Famennian (Upper Devonian) of Latvia and Central Russia

The recent find of an ethmosphenoid of Glyptopomus bystrowi (Gross 1941), a “glyptopomid” tetrapodomorph, in the Ketleri Formation (Upper Famennian, Upper Devonian) in western Latvia induced the description of historical material from this site and almost coeval localities in Central Russia (Orel-Saburovo Beds, Plavskian Regional Stage). Detailed morphological studies allowed recognition of new characters which support the taxonomic position of this species. Three-dimensional preservation of isolated elements enable the description of internal cranial structures, like the posterodorsolateral expansion of prenasal pits, the passage of some nerves and blood vessels, unknown in the previously described species of this genus. Despite minor differences, the vertebrate assemblages from these areas fit within the placoderm B. ciecere Zone (VII), which corresponds to the ?Upper postera–Lower expansa conodont Zone interval. These assemblages are virtually the same in their composition, except that durophagous placoderms and dipnoans are present in the Central Russian sites, in contrast to the Latvian ones. This could be explained by more significant marine influences.