A dearth of diplobathrids (Crinoidea) from the type Devonian System, SW England

Abstract

Summary The diverse biota from the marine deposits of the type area of the Devonian System was monographed by the Reverend George Ferris Whidborne, MA, FGS (1846–1910) between 1889 and 1907. Most well-preserved specimens of crinoids are cladids or monobathrids from the Middle and Upper Devonian of south and north Devon, respectively. The camerate crinoids are dominated by the monobathrid Hexacrinites spp., known from many thecae and several nominal species from the Middle Devonian Torquay Limestone Formation; other monobathrids are moderately common in the Upper Devonian. The dicyclic diplobathrid camerates are less speciose and are commonly poorly preserved. Diplobathrids include Rhodocrinites ? sp. A (poor crown) and Rhodocrinites ? sp. B (columnals); Acanthocrinus sp. (spinose thecal plate); Gilbertsocrinus sp. A (columnals); non Rhipidocrinus crenatus (Goldfuss) (possibly a monobathrid crown); Thylacrinus ? sp. (fragment of theca); and rhodocrinitid? sp. indet. This is in stark contrast to the 5 genera and 9 nominal species of diplobathrids known from the lower Silurian, and the 3 genera and 14 nominal species in the Mississippian of the British Isles, many of which are known from multiple, well-preserved specimens. The potential reasons for this disparity are many, but must include lack of effort by collectors over the past 100+ years, limited outcrop area, poor preservation due to tectonic deformation and, probably, a genuine rarity of diplobathrids in the British Isles during the Devonian.