The hexactinellid sponge Cyathophycus from the Upper Ordovician of the Argentine Precordillera

CARRERA, M.G.; ORTEGA, G.

AMEGHINIANA

ASOCIACION PALEONTOLOGICA ARGENTINA

Lugar: Buenos Aires; Año: 2009 vol. 46 p. 449 - 459

0002-7014

A nearly complete specimen of a hexactinellid sponge has been recovered from LowerOrdovician siliciclastic rocks of the Argentine Precordillera. The material was collected in the upper memberof the Los Azules Formation (Sandbian). A new species of the genus Cyathophycus Walcott, C. extendis,is erected. The taxonomic position of the genus is still controversial. Their recent assignment to the familyDictyospongiidae is discussed; Cyathophycus has been considered as a transitional form between protospongiidswith simple regular skeletons and dictyospongiids with more complex skeletons. Previousstudies have stated that hexactinellid evolution through the Cambrian-Ordovician interval, like othersponge groups at this time, appears to have been based on strengthening the skeleton, and the occupationof more turbulent, shallow-water environments, while remaining dominant in deep-water settings.Cyathophycus is a typical representative of this transitional stage in which the skeleton is simple, but double-layered, with bundled spicule rays, and not as rigid as the typical dictyosponge skeletons. Lower andMiddle Ordovician records are from black shale deposits, while younger occurrences show slightly differentenvironmental settings (mudstone, shaly mudstone and dolomites), which indicate shallower butstill quiet water deposits.