''Rotaciurca'' is an extinct genus of

Silurian The Silurian ( ) is a geologic period and system spanning 23.5 million years from the end of the Ordovician Period, at million years ago ( Mya), to the beginning of the Devonian Period, Mya. The Silurian is the third and shortest period of t ...

cephalodiscid pterobranchs. The genus contains a single species, ''Rotaciurca superbus'', known from the Bertie Group of

Ontario Ontario is the southernmost Provinces and territories of Canada, province of Canada. Located in Central Canada, Ontario is the Population of Canada by province and territory, country's most populous province. As of the 2021 Canadian census, it ...

, Canada.

Description

''Rotaciurca'' is a pseudocolonial (containing multiple clustered individuals which are not connected) pterobranch, unique for being a cephalodiscid rather than a

graptolite Graptolites are a group of colonial animals, members of the subclass Graptolithina within the class Pterobranchia. These filter-feeding organisms are known chiefly from fossils found from the Middle Cambrian ( Miaolingian, Wuliuan) through t ...

. The cluster consists of a ring of radiating tubes, likely containing the living individuals, attached to a conical structure interpreted as a float, giving the original fossil the nickname of "

Ezekiel Ezekiel, also spelled Ezechiel (; ; ), was an Israelite priest. The Book of Ezekiel, relating his visions and acts, is named after him. The Abrahamic religions acknowledge Ezekiel as a prophet. According to the narrative, Ezekiel prophesied ...

's wheel". The whole organism is roughly long, seemingly with two distinct rows of tubes. Its pterobranch affinity is confirmed by lineations within the tubes, which are traces of fuselli, and the irregular arrangement of these group it with the cephalodiscids. ''Rotaciurca'' has a number of similarities to '' Yuknessia'', another enigmatic fossil recently described as a pterobranch, including rigid and similarly sized tubes, although those of ''Yuknessia'' are much finer and have more tightly packed fuselli.

Ecology

''Rotaciurca'' has been interpreted as a planktonic filter-feeder, with the conical float providing buoyancy like that of a

Portuguese man o' war The Portuguese war (''Physalia physalis''), also known as the man-of-war or bluebottle, is a marine hydrozoan found in the Atlantic Ocean and the Indian Ocean. It is the only species in the genus ''Physalia'', which in turn is the only genus in ...

. It is unique in this aspect, as all other known cephalodiscids are benthic and sessile, while the only other planktonic pterobranchs are graptolites, which shows the water column was colonised several times by hemichordates.

Distribution

''Rotaciurca'' is known from ten specimens, with the holotype nearly complete. Unusually for a planktonic animal, it has only been found in one locality, that being the Bertie Group, however since it was likely soft-bodied, the exceptional preservation of this site may have been necessary for ''Rotaciurca'' to fossilise.

Etymology

''Rotaciurca'' is named in honour of Samuel J. Ciurca, Jr., who donated thousands of eurypterid fossils to the Yale Peabody Museum, alongside the Latin word ''rota'', meaning "wheel". Its specific name, ''superbus'', from the Latin word meaning "beautiful", acknowledges that Ciurca labelled the holotype fossil "the most beautiful fossil ever found".

References

{{taxonbar, from1=Q125555760, from2=Q125555780 Silurian Ontario Pterobranchia Fossil taxa described in 2023