Exceptional soft-tissue preservation reveals the oldest evidence for tube feet and their ecological significance in crinoids

Tube feet are extensions of the echinoderm water vascular system that play essential roles in feeding and ecology in living crinoids. However, only a single instance of tube foot preservation has been described across the 485-million-year fossil record of crinoids, which limits our understanding of soft-tissue morphology and functional ecology within this major clade of echinoderms. Here, we report on the earliest example of tube feet preserved in the crinoid Dendrocrinus simcoensis from the Late Ordovician Neuville Lagerstätte of Québec, Canada. The tube feet are preserved as pyrite films and exhibit morphology that is broadly similar to that of extant comatulid crinoids, but with combinations of length and spacing that differ from those documented in any extant crinoid. Spacing of tube feet in D. simcoensis is significantly similar to that inferred for other fossil crinoids based on ambulacral cover plates, especially other eucladid crinoids, and reveals a strong relationship between tube foot spacing, phylogeny and palaeoecology. The unique combination of tube foot length and spacing in D. simcoensis suggests this crinoid may have fed with the arms oriented in a multidirectional or conical posture, unlike most modern stalked crinoids.