Progress in the discovery of extant and fossil bryozoans

The number of species that exist on Earth has been an intriguing question in ecology and evolution. For marine species, previous works have analysed trends in the discovery of extant species, without comparison to the fossil record. Here, we compared the rate of description between extant and fossil species of the same group of marine invertebrates, Bryozoa. There are nearly 3 times as many described fossil species as there are extant species. This indicates that current biodiversity represents only a small proportion of Earth's past biodiversity, at least for Bryozoa. Despite these differences, our results showed similar trends in the description of new species between extant and fossil groups. There has been an increase in taxonomic effort during the past century, characterized by an increase in the number of taxonomists, but no change in their relative productivity (i.e. similar proportions of authors described most species). The 20th century had the most species described per author, reflecting increased effort in exploration and technological developments. Despite this progress, future projections in the discovery of bryozoan species predict that around 10 and 20% more fossil and extant species than named species, respectively, will be discovered by 2100, representing 2430 and 1350 more fossil and extant species, respectively. This highlights the continued need for both new species descriptions and taxonomic revisions, as well as ecological and biogeographical research, to better understand the biodiversity of Bryozoa.