The early L udfordian leintwardinensis graptolite Event and the G orstian– L udfordian boundary in B ohemia ( S ilurian, C zech R epublic)

The late G orstian to early L udfordian hemipelagic succession of the south‐eastern part of the P rague S ynform preserves a rich fossil record dominated by 28 species of planktic graptoloids associated with pelagic myodocopid ostracods, pelagic and nektobenthic orthocerid cephalopods, epibyssate bivalves, nektonic phyllocarids, rare dendroid graptolites, brachiopods, crinoids, trilobites, sponges and macroalgae. Faunal dynamics have been studied with particular reference to graptolites. The early L udfordian leintwardinensis graptolite extinction Event manifests itself as a stepwise turnover of a moderate diversity graptolite fauna rather than an abrupt destruction of a flourishing biota. The simultaneous extinction of the spinose saetograptids S aetograptus clavulus , S aetograptus leintwardinensis and the rare S . sp. B . at the top of the S .  leintwardinensis Z one was preceded by a short‐term acme of S . clavulus . C ucullograptus cf. aversus and C . rostratus vanished from the fossil record in the lower part of the B ohemograptus tenuis B iozone. No mass proliferation of B ohemograptus has been observed in the postextinction interval. Limited indigenous speciation gave rise to P seudomonoclimacis kosoviensis and P seudomonoclimacis cf. dalejensis . E gregiograptus (the only novel element of cryptic origin) made its earliest occurrence in association with the latest cucullograptids. A postextinction graptolite assemblage of moderate diversity, composed for the most part of long‐ranging taxa, persisted through the middle and upper tenuis B iozone until new rediversification in the N eocucullograptus inexpectatus B iozone. Unlike the graptoloids, the planktic, epiplanktic, nektonic and nektobenthic shelly fauna did not suffer significant extinction in the early L udfordian. The G orstian– L udfordian boundary is placed at the lowest occurrence of S . leintwardinensis in spite of the very modest graptolite record available from the L udfordian GSSP where no graptolites occur below the basal bed of the L ower L eintwardine F ormation. Elsewhere, the G orstian– L udfordian boundary has been placed at the base of the S aetograptus linearis B iozone which has been considered roughly correlative with the leintwardinensis B iozone. Indeed, our morphometric study places the worldwide biozonal index species S . linearis in synonymy with S .  leintwardinensis and thus considerably enhances the biostratigraphical utility of the latter index species. P seudomonoclimacis antiqua sp. nov. is described.