Chinese origin and radiation of the Palaeozoic crinoid family Petalocrinidae

Abstract

The Ordovician to Devonian family Petalocrinidae includes 28 species belonging to 5 genera. This family is unique because the arm plates are fused into a large fan or cylinder. Paleobiogeographic occurrences of this family include Laurentia, Baltica, Avalonia, South China, Sibumasu, and Perunica blocks. The family has the oldest petalocrinids from China. An early radiation of this clade resulted in three genera during the Llandovery of China. Petalocrinus became cosmopolitan during the Llandovery and Wenlock, and the youngest genus is present in the Lower Devonian of the Czech Republic. Taxonomic determination for the Petalocrinidae is based on the fused arm plates instead of cup plates. The diverse morphology of these arm plates suggests a variety of aerosol suspension-feeding modes may have been used by petalocrinids.

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

“…As noted in Mao et al (2015), this arm morphology may have been an adaptation to the multidirectional flow conditions present in a reefal setting. Also, on Spirocrinus arms, the ambulacral groove was much wider than on species of either Petalocrinus or Sinopetalocrinus, which is an indication that Spirocrinus individuals fed on a wider range of food sizes (Ausich, 1980).…”

“…Terminology and classification follows Weller and Davidson (1896), Bather (1898), Lane and Moore (1978), Mu and Lin (1987), and Mao et al (2015). All measurements are in mm (millimeters).…”

“…Superfamily Gasterocomacea Roemer, 1854 Family Petalocrinidae Weller and Davidson, 1896 Remarks.-According to Mao et al (2015), the Petalocrinidae has a relatively small aboral cup with arms, each presumably a series of fused brachials. These specialized arm plates are robust and can be transported as isolated plates after death.…”

“…Alternatively, a more typical Petalocrinus species (e.g., P. inferior) evolved into Sinopetalocrinus by the expansion of the ambulacra from only the aboral surface to both the oral and aboral surfaces 9). The increased length of the ambulacra on an arm allowed particle capture on both the oral and aboral sides of the arm (Mao et al, 2015). Again, this configuration may be better adapted to the multidirectional flow conditions present in a reefal setting.…”

“…Other older genera are from the Shihniulan and equivalent Leijiatun formations. Therefore, Aeronian sequences in Guizhou have potential to increase the biodiversity of the family (Mao et al, 2015).…”