Lower and Middle Jurassic Perispyridium (Radiolaria) from the Snowshoe Formation, East-Central Oregon

Abstract

The bizarre Jurassic spumellarian-like nassellarian genus Perispyridium is noteworthy not only for its potential as a biostratigraphic marker, but also because its skeletal morphology reveals the extent to which the nassellarian Bauplan can (and cannot) be modified in response to selection. The Perispyridium skeletal phenotype is unique in several respects from all other nassellarian groups including all members of the family Eptingiidae. On the basis of the distinctive arrangement of skeletal structures, and the lack of obvious skeletal homologies with the other eptingiid species, it is recommended that Perispyridium be regarded as internally monophyletic but provisionally placed within the nassellarian incertae sedis until such time as phylogenetic relationships within the Mesozoic nassellaria are better understood. Similarities between Perispyridium and the Triassic eptingids may be an example of homeomorphy within the Radiolaria. Thirteen new species of Perispyridium are described and illustrated including P. darwini, P. dobzhanskyi, P. elegans, P. gouldi, P. hennigi, P. mayri, P. olsoni, P. pessagnoi, P. robustum, P. schopfi, P. simpsoni, P. slaughteri, and P. triangularium.