Pseudopholidops – the earliest craniopside (Brachiopoda, Craniiformea): an extinction survivor

Four craniopside species of Pseudopholidops from the East Baltic and Iran, including P. ingriana sp. nov., are described. Pseudopholidops is the earliest yet documented craniopside, first appearing in the upper Darriwilian of Estonia. Like other craniiforms, Pseudopholidops has a lecithotrophic larval stage, settling on the ventral side of the body, and the secretion of the ventral valve is delayed until the end of metamorphosis. For the first time, the presence of a cicatrix attachment and a small posterior muscle (=levator ani) are recorded for the genus. Phylogenetic analysis supports previous observations that the craniopsides, probably represent a paraphyletic stem group within the subphylum Craniiformea. The results also suggest a monophyletic origin of Pseudopholidops. The genus first appeared during the Late Ordovician of the Baltoscandian Basin and by the late Katian had dispersed towards Mediterranean peri-Gondwana. The genus soon acquired a wide geographical distribution, as a minor component of the Hirnantian brachiopod fauna, at the time of the terminal Ordovician glaciation; it survived into the Llandovery (Aeronian) in the Alborz Region of Iran. The phylogenetic analysis indicates that the Devonian craniopside Lingulapholis may represent a distant descendant of Pseudopholidops.