Palaeoecology of the pseudoplanktonic Triassic crinoid Traumatocrinus from Southwest China

Colonies of Traumatocrinus (Echinodermata, Crinoidea, Encrinida) attached to driftwood from the Late Triassic (Carnian) Xiaowa Formation of the Guanling area (Guizhou, Southwest China) give evidence for a pseudoplanktonic lifestyle of this specialized offshoot of the otherwise benthic Middle Triassic family Encrinidae. The stem of Traumatocrinus individuals may exceed 11 m in length. Colonies attached by root cirri to logs of driftwood may consist of more than 150 individuals. After the end-Carnian extinction of Traumatocrinus, its ecological niche was taken over in Norian times by Seirocrinus and Pentacrinites with convergent morphological modifications. Seirocrinus and Pentacrinites were derived from the Middle Triassic benthic articulate crinoid family Holocrinidae. After the Toarcian (Lower Jurassic), the niche occupied by Pentacrinitidae disappeared, possibly because of the emergence of wood-boring bivalves and their destructive impact. Due to a larval and adult planktonic and pseudoplanktonic lifestyle, the pelagic Traumatocrinidae were dispersed over the Triassic seas. While genus Traumatocrinus was a Palaeo-Tethys faunal element, its sister genus Vostocovacrinus inhabited the Boreal realm.