The first fossil entoproct

Abstract

It has long been appreciated that the fossil record is strongly biased towards groups with mineralized skeletons. If most or all animal phyla originated in the Precambrian [1], then many softbodied phyla must have long histories unrepresented in the fossil record. Among these are the Entoprocta, a small phylum of aquatic metazoans. The only supposed fossil entoproct is the Cambrian genus Dinomischus [2-4] . However, body size in Dinomischus is at least an order of magnitude greater than that of any Recent entoprocts: D. isolatus from the Middle Cambrian Burgess Shale of Canada is over 25 mm long, and D. venustus from the Lower Cambrian Quiongzhusi Formation of China exceeds 100 mm in length. Furthermore, the "tentacles" of Dinomischus are stiff bracts unlike the flexible tentacles of entoprocts, and other morphological details supporting an entoproct affinity are poorly preserved or lacking. Assignment of Dinomischus to the Entoprocta must therefore be regarded as very doubtful. Here, we report the first unequivocal fossil entoproct, a Late Jurassic species belonging to the extant genus Barentsia. We describe its bioimmured preservation, and comment on its evolutionary significance. Early naturalists included the entoprocts within the phylum Bryozoa (= Ectoprocta), but the many important differences between entoprocts and