New taxa and phyletic evolution of the Aeronian (Llandovery, Silurian) Petalocrinidae (Echinodermata, Crinoidea) in Guizhou, South China Block

Abstract

Systematic paleontology of three new species of Petalocrinidae (Crinoidea) are documented from the carbonate-dominated units of the Shihniulan and equivalent Leijiatun formations (Llandovery, Silurian) of the Baisha, Fengxiang, and Shuibatang sections in Guizhou (China). New taxa are from the Upper Yangtze Epicontinental Sea of the South China Block. The new taxa include Petalocrinus stenopetalus new species, Spirocrinus circularis new species, and S. dextrosus new species. They have a narrow spatial and temporal (Aeronian) distribution. Evolutionary patterns of the four genera of Petalocrinidae are outlined based on the specialized characters of the fused arm plates. Phylogenetic analysis was used to assess morphological relationships within the Petalocrinidae. Petalocrinus inferior represents the plesiomorphic condition for the group and nests as a sister group of P. stenopetalus n. sp. and the Spirocrinus species used in this analysis and the clade exclusively comprised of Sinopetalocrinus. The phylogenetic analysis suggests that Petalocrinus, as currently defined, might be a paraphyletic genus.