Bryozoans, also referred to as the Polyzoa, are an ancient phylum of tiny aquatic invertebrate animals that mostly live in colonies. Normally marine, but some species do live in freshwater, they have a protective exoskeleton made from calcium carbonate. They have a special feeding appendage called a lophophore, which resembles a crown of tentacles used for filter feeding.

Bryozoan fossils are abundant and geographically widespread and the presence of six major orders of bryozoans in Lower Ordovician strata strongly indicated that these organisms evolved during the Cambrian, however, fossil evidence was lacking. Late last year (2021), a team of researchers published a paper in the academic journal “Nature” describing a new genus of soft-bodied bryozoan from the Early Cambrian of Australia and southern China. Named Protomelission gatehousei, its fossils confirm a Cambrian origin for these important aquatic organisms.

Bryozoan fossil from the Early Cambrian.
Protomelission gatehousei from the Cambrian Wirrealpa Limestone, South Australia. Picture credit: Zhang et al.

A Basal Member of the Bryozoa

The researchers from Macquarie University (Sydney, Australia), the Northwest University (Xi’an, China), the London Natural History Museum, the University of Missouri, the Nanjing Institute of Geology and Palaeontology (Nanjing, China) as well as the Swedish Museum of Natural History (Stockholm, Sweden), describe this new genus as a basal member of the order.

The discovery of a stem bryozoan from rocks dating from the Cambrian narrows the origination gap that previously existed between the known fossil record and independent molecular clock estimates. The researchers state that this fossil discovery pushes back the fossil record of the Bryozoa by approximately thirty-five million years.

Protomelission gatehousei confirms that the colonial body plan of the Bryozoa originated in the Early Cambrian. It also reconciles the fossil record with molecular clock estimations of an Early Cambrian origination and subsequent Ordovician radiation of Bryozoa following the acquisition of a carbonate skeleton.

Bryozoan fossil from the Ordovician.
Fossils of a branching bryozoan colony from the Ordovician. The presence of six major orders of bryozoans in Lower Ordovician rocks strongly suggests a Cambrian origin for the largest and most diverse lophophorate phylum but the fossil evidence had been lacking. A newly published paper describes Protomelission gatehousei from the Early Cambrian of Australia and southern China and confirms a Cambrian origin for these important aquatic organisms.

Whilst the Cambrian and Ordovician forms are extinct, modern bryozoans are an important constituent of modern-day marine fauna.

The scientific paper: “Fossil evidence unveils an early Cambrian origin for Bryozoa” by Zhiliang Zhang, Zhifei Zhang, Junye Ma, Paul D. Taylor, Luke C. Strotz, Sarah M. Jacquet, Christian B. Skovsted, Feiyang Chen, Jian Han and Glenn A. Brock published in Nature.