Tracing the origin of the planktic graptolites (Hemichordata, Pterobranchia) through the Furongian Gap (Upper Cambrian)

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The Furongian (late Cambrian) time interval is the key interval to understand the origin and early evolution of planktic graptoloids (Graptolithina: Pterobranchia) and the starting point for the geological application of graptolites in biostratigraphy, long after the origination of the graptolites in the basal Cambrian. Unfortunately, the ‚Furongian Gap‘, an interval of low fossil yield that needs to be filled, masks our understanding of the origin and early evolution of planktic graptolites. It appears that planktic graptoloids suddenly originated at the base of the Ordovician and little is known about their early evolutionary changes during this time interval. The Furongian Guole lagerstätte of S. China yield a diverse benthic graptolite fauna, which, together with the investigation of early planktic graptolite faunas from the Cambrian/Ordovician GSSP section at Green Point (Newfoundland, Canada) and the Dayangcha section (N. China) will shed light on this chapter in the evolution of the graptolites and their exploration of the oceanic environment in the early Paleozoic. The origin of planktotrophy in the graptolites and the associated modifications in their tubarium formation led to the earliest macro-plankton populating the expanses of the world’s oceans, before nektic organisms and plankton feeders outcompeted these organisms in the early Devonian.