Caught in the Cambrian Explosion: The mystery of the early evolution of the Pterobranchs (Hemichordata, incl. Graptolithina) and their evolutionary innovations

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The Cambrian explosion is the time interval when most of modern phyla originated. However, the fossil record only in part supported this idea. First definitive pterobranch hemichordates (e.g. graptolites and their relatives) are common in the Middle Cambrian (Series 3, Stage 5), but the evidence for the presence of even earlier taxa is mounting. These taxa are close to the evolutionary origin of the pterobranchs and shed light on the phylogenetic relationships to the remaining hemichordates (e.g. Enteropneusta). New palaeontological methods of chemical extraction of organically preserved organismic remains help to unravel the early history of the evolution of early hemichordates and especially pterobranchs. Shallow water dark shale and limestone successions yield a fossil archive of immense value not yet explored. These strata start to yield unexpected richness of organically preserved body fossils (also known as SCFs; Small carbonaceous fossils) aside the more normal mineral preservation of fossil shells, the typical Cambrian shelly faunas (e.g. Small Shelly Faunas; SSFs). The Lower Cambrian Forteau Formation of western Newfoundland provides a sedimentary succession with low thermal overprint and moderate tectonic distortion that is ideal for the fossil extraction with the means of acidic dissolution, especially with gentle hydrofluoric acid techniques. Additionally, research will be done in the Chinese Kaili Formation, a well-known lagerstätte with spectacular fossil preservation on a different palaeo-continent. The Lower Cambrian in many regions of the world lacks sufficient and widely enough distributed macrofossils for a detailed biostratigraphy. Conventional fossil zones or assemblages have been questioned recently due to uncertainties of international correlation. The extraction of organically preserved fossils provides a new tool support the biostratigraphy of the Lower Cambrian. It also helps to better understand tempo and mode of the Cambrian explosion by focusing on groups of organisms not usually recognized in the fossil assemblages.