Experimental neoichnology of crawling stalked crinoids

Abstract

Stalked crinoids have long been considered sessile. In the 1980s, however, observations both in the field and of laboratory experiments proved that some of them (isocrinids) can actively relocate by crawling with their arms on the substrate, and dragging the stalk behind them. Although it has been argued that this activity may leave traces on the sediment surface, no photographs or images of the traces produced by crawling crinoids have been available. Herein, we present results of neoichnological experiments using the shallowest species of living stalked crinoid, Metacrinus rotundus, dredged from Suruga Bay (near the town of Numazu, Shizuoka Prefecture, * 140 m depth). Our results demonstrate that isocrinids produce characteristic locomotion traces, which have some preservation potential. They are composed of rather deep and wide, sometimes weakly sinuous, central drag marks left by the stalk and cirri, and short, shallow scratch marks made by the arms. Based on the functional morphology and taphonomy, it has been argued that the ability to autotomize the stalk and relocate had already evolved in the oldest stem-group isocrinids (holocrinids), likely in response to increased benthic predation pressure during the so-called Mesozoic marine revolution. Our data show that this hypothesis may be corroborated in the future by ichnological findings, which may provide more direct proof of active locomotion in Triassic holocrinids.

Predation in the marine fossil record: Studies, data, recognition, environmental factors, and behavior

“…Over the Mesozoic, Gorzelak et al (2012) found that genus richness of sessile crinoids is negatively correlated with that of predatory sea urchins, whereas a positive correlation was suggested between motile crinoids and predatory sea urchins. They argued that crinoid motility is an effective escape strategy, which is consistent with evidence of crawling by extant and fossil stalked crinoids and the crawling and swimming abilities of comatulid crinoids (Baumiller and Messing, 2007;Brom et al, 2018;Meyer and Macurda, 1977;Neto de Carvalho et al, 2016). A similar conclusion was reached for post-Paleozoic crinoids: the appearance and evolutionary success of motile crinoids starting in the Triassic was suggested to be related to the radiation of echinoid predators with more advanced feeding apparatuses (Baumiller et al, 2010a) or the rise of bony fishes (Meyer and Macurda, 1977).…”

Experimental neoichnology of post-autotomy arm movements of sea lilies and possible evidence of thrashing behaviour in Triassic holocrinids

“…Specimens of living stalked crinoids of Metacrinus rotundus were used in this study. Sampling and handling of these specimens followed described procedure 12 – 14 . Crinoids were dredged from Suruga Bay (near the town of Numazu, Shizuoka Prefecture; Japan; ~ 35° 3′ N, ~ 138° 48′ E, ~ 140 m depth) from the sea bottom using a 90-cm-wide naturalist dredge with a net.…”