Parasitism of Paleozoic Crinoids and Related Stalked Echinoderms: Paleopathology, Ichnology, Coevolution, and Evolutionary Paleoecology

The mid-Paleozoic was punctuated by a rapid radiation of durophagous (shell-crushing) predators. These new predators were primarily placoderm and chondrichthyan fishes but probably also included phyllocarid and eumalacostracan arthropods. Coincident with the radiation of these durophages, beginning in the mid-Devonian, there was an increase in the frequency of predation-resistant morphologies in a variety of marine invertebrate taxa. Among bellerophontid molluscs, disjunct coiling disappeared and umbilici became less common while the frequency of genera with sculpture increased. The abundance of brachiopod genera with spines on one or both valves increased dramatically. Sculpture became more pronounced and common among genera of coiled nautiloids. Inadunate and camerate crinoids showed a marked increase in spinosity, and all three crinoid subclasses tended to develop thicker thecal plates. Show more

… the snail, whose tender horns being hit Shrinks backward in his shelly cave with pain, And there, all smothered up, in shade doth sit, Long after fearing to creep forth again…. — William Shakespeare, Venus and Adonis (1593) For many decades, ecology textbooks presented classical competition theory without reservation. The central principle here is that two species sharing an essential resource that is in limited supply cannot coexist for long because the competitively superior species will eliminate the other one. The implication is that ecological communities should be characterized by division of resources among species, or niche partitioning. Thus, it is understandable that many paleontologists have continued to invoke concepts of competitive exclusion and niche partitioning in their studies of ancient guilds and communities. By now, however, there is a large body of neontological literature demonstrating that interspecific competition and resource partitioning play only a minor role in many ecological communities—especially benthic marine communities, which are the primary focus of the following discussion. Predation and physical disturbance inflict so much damage on biotas of the seafloor that populations of one species seldom monopolize a potentially limiting resource, except sporadically and locally. As a result, it is uncommon for any species to drive another to extinction through competitive exclusion—or even to force another species to drastically change its exploitation of any environmental resource throughout its geographic range. Furthermore, what particular species or group of species occupies a particular microhabitat is often simply a matter of time of arrival. Show more