International Geologiical Congress - Oslo 2008


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HPF-13 Major events in the evolution of marine biota


Early Mesozoic Crinoid evolution revolution


Tomasz Baumiller, University of Michigan (United States)
Mariusz Salamon, University of Silesia (Poland)
Przemyslaw Gorzelak, University of Silesia (Poland)


Predation is considered an important, though not uncontroversial, factor in evolution. A variety of trends have been interpreted in the context of predator-prey interactions, including those that characterizing crinoids. Increasing armoring of Paleozoic crinoids, offshore displacement of stalked crinoids in the Late Mesozoic, distribution of autotomy planes in arms of articulates, crawling and swimming abilities among comatulids, have all been linked to predation. Several of these have been used to illustrate some of the best known global trends, such as the Mid Paleozoic Marine Revolution, Mesozoic Marine Revolution, and onshore-offshore patterns. Here, we provide data on predation on Mesozoic crinoids and suggest that the high frequency of these interactions in the Late Triassic and the appearance of most of the articulate crinoid body plans at this time were causally connected. We refer to this event as the Early Mesozoic Crinoid Evolution Revolution.
Fossil and Recent data indicate that crinoids suffer from predation by fishes, arthropods, asteroids and echinoids. Using samples of disarticulated crinoids from numerous Mesozoic localities, we looked for evidence of bite marks on stalk elements from Triassic, Jurassic, and Cretaceous localities in Poland. Many columnals possessed scratches and pits similar to those made by Recent cidaroids. The scratches are relatively shallow cuts on the ossicle surface; pits are usually perpendicular to the surface and circular in outline. These marks are on the lateral faces of ossicles, rather than on the articular facets, suggesting that they were made while elements were still articulated, an interpretation consistent with numerous examples of such marks on well preserved pluricolumnals. Given the rapid rates of post-mortem disarticulation of crinoids in natural settings, these data suggest that the crinoid material was fresh, most probably live, when the marks were made, and we treat it as evidence of predation. We were unable to recognize regenerated stereom, which suggests that bite marks were all lethal.

The Late Triassic and the Triassic-Jurassic boundary represent critical phases of post-Paleozoic crinoid evolution. Following the Permo-Triassic, which led to their near extinction, crinoids rebounded rapidly in the Middle and Late Triassic. This radiation led not only to a rapid expansion through morphospace, but the attainment of great ecological diversity. Most of the major functional "experiments" in post-Paleozoic crinoids that occurred at this time can be described in terms of predation including planktonic microcrinoids (roveacrinids), pseudoplanktonic stalked crinoids (traumatocrinids), stalk and arm shedding benthic crinoids (isocrinids, holocrinids), free moving crinoids (paracomatulids) and pseudoplanktonic isocrinids (pentacrinids). It is highly probable that the evolution of morphologies and behaviors of the above mentioned groups was stimulated by their interactions with predators.


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