Experimental neoichnology of crawling stalked crinoids

Krzysztof R Brom,Przemysław Gorzelak,Tatsuo Oji,Kazumasa Oguri,Mariusz A Salamon

doi:10.1007/s13358-018-0158-9

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.

Highlights

One of the most fascinating and surprising traits of some Recent stalked crinoids, the isocrinids, is their locomotion ability
Our results demonstrate that isocrinids produce characteristic locomotion traces, which have some preservation potential
The most common, produced during locomotion on a more or less straight path, were horizontal traces composed of median trails left by the stalk and cirri dragged on the bottom (Fig. 2a, b, d, e), and lateral short tracks made by the crawling arms (Fig. 2a, c, d, f)

Summary

Introduction

One of the most fascinating and surprising traits of some Recent stalked crinoids, the isocrinids, is their locomotion ability. Two basic types of isocrinid locomotion have been distinguished: (1) the so-called finger-tip pull, where the crawling involves a repeating sequence of movements by the proximal portions of the leading arms only, bending sharply away from the substrate; and (2) the so-called elbow-crawl, where traction with the substrate is provided by the pinnule-covered oral side of the middle third to distal half of the arms that remain strongly flexed aborally (Baumiller and Messing 2007). It has been only mentioned that crawling isocrinids produce two types of traces: (1) a drag mark left by the stalk, and (2) short radiating scratch marks around the central drag (Messing et al 1988)

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Conclusion