Abstract
AbstractEvolving interactions between predators and prey constitute one of the major adaptive influences on marine animals during the Paleozoic. Crinoids and fish constitute a predator–prey system that may date back to at least the Silurian, as suggested by patterns of crinoid regeneration and spinosity in concert with changes in the predatory fauna. Here we present data on the frequency of breakage and regeneration in the spines of the Middle Devonian camerateGennaeocrinusand late Paleozoic cladids, as well as an expanded survey of the prevalence of spinosity and infestation by platyceratid gastropods on crinoid genera during the Paleozoic. Spine regeneration frequency in the measured populations is comparable to arm regeneration frequencies from MississippianRhodocrinitesand from modern deep-water crinoid populations. The prevalence of spinosity varies by taxon, time, and anatomy among Paleozoic crinoids; notably, spinosity in camerates increased from the Silurian through the Mississippian and decreased sharply during the Pennsylvanian, whereas spines were uncommon in cladids until their Late Mississippian diversification. Among camerates, tegmen spinosity is positively correlated with the presence of infesting platyceratid gastropods. These results allow us to evaluate several hypotheses for the effects of predation on morphological differences between early, middle, and late Paleozoic crinoid faunas. Our data corroborate the hypothesis that predators targeted epibionts on camerate crinoids and anal sacs on advanced cladids and suggest that the replacement of shearing predators by crushing predators after the Hangenberg extinction affected the locations of spines in Mississippian camerates.
Highlights
Regeneration frequency in modern crinoid populations reflects the presence and frequency of predation (Meyer and Macurda 1977; Bourgoin and Guillou 1994; Baumiller 2013b), and damaged and regenerating body parts can be used to infer the intensity of predation on fossil crinoid populations as well (Oji 2001; Baumiller and Gahn 2004; Gahn and Baumiller 2005, 2010; Syverson et al 2014)
The unusual branching form of the tegmenal spines makes it impossible to perform the adjustment for postmortem breakage, and in many specimens the evidence for regeneration was ambiguous, so this estimate should be regarded as less reliable than the values for the late Paleozoic sample
In the late Paleozoic sample taken as a whole, 98% of spines were broken
Summary
Predation constitutes a substantial source of adaptive pressure on crinoids, and many researchers have hypothesized that it has been a primary driver of their morphological and ecological evolution (Signor and Brett 1984; Meyer 1985; Oji and Okamoto 1994; Baumiller et al 2008; Baumiller and Gahn 2012; Syverson and Baumiller 2014). Modern crinoids may autotomize arms during ontogeny (Roux 1976; Nakano et al 2004; Obuchi et al 2010) or under stress (Baumiller 2003b; Nichols 1996), modern stalked crinoids have few sources of injury other than predation (Mladenov 1983; Meyer 1985; Oji 1996; Lawrence 2009; Veitch et al 2015), which is generally inferred to have been inflicted mainly by fishes (Meyer 1985; Waters and Maples 1991; Gahn and Baumiller 2010) and echinoids (e.g., Baumiller et al 2008, 2010; Schneider 2001; Lach et al 2015; Stevenson et al 2017). We will instead use the terms “complete” and “partial” predation, addressing the physiological outcome for the crinoid only and avoiding discussion of predator strategy
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