Geological Society of America Annual Meeting

Geological Society of America Annual Meeting
Date: 27-30 October 2013
Place: Denver, Colorado

PRESENTATIONS and ABTRACTS

1) Syverson, V.J. and Baumiller, T.K. 2013. Spinosity over time in Paleozoic crinoids and its implications for predation pressure.

Predation intensity is hypothesized to have increased during the Phanerozoic, driving corresponding increases in anti-predatory defensive adaptations. The Mid-Paleozoic marine revolution has been identified as an episode during which durophagous nektonic fish predators became more common and, it has been argued, resulted in an increase of defensive adaptations in benthic organisms. Similarly, increases in predatory injuries in camerate crinoids from the Ordovician to the Mississippian correspond to an increase in frequency of camerate arm branching patterns that reduce the probability of arm loss during encounters with predators. Spines and nodes represent another commonly suggested adaptation that may have multiple anti-predatory functions, and it has been claimed that they increased among crinoids during the Mid-Paleozoic marine revolution. Such calycal growths have several possible defensive functions against predators and parasites, such as increasing effective size, distributing bite force, and disrupting parasite settling. Herein we describe patterns of change in the presence and location of spines and nodes in crinoids during the Paleozoic, based on genus descriptions compiled in the Treatise on Invertebrate Paleontology, and use them to discuss the possible relationships between defensive adaptations in the different Paleozoic crinoid suborders and the evolution of their predators and parasites.

2) Baumiller T.K. Reconstructing predation intensities from injuries: theoretical and practical considerations

Predation and its ecological and evolutionary consequences has been an important theme in paleobiology and its study in the fossil record has often focused on injuries. Although both biotic and abiotic factors may lead to injuries, those resulting from interactions with predators can often be recognized or inferred. Of special evolutionary importance are those injuries that are non-lethal because they are detrimental to a variety of physiological functions, their healing requires a substantial investment of energy, and thus they are likely to represent a strong agent of selection. The evolutionary impact of such non-lethal injuries is related to the rate at which they are produced, therefore determining the rate of the injury-producing process is of some interest. Commonly, data on injury frequencies have been employed as a proxy for this rate, and if injuries are shown as being a consequence of predation, this rate has been considered as equivalent to “predation intensity” or “predation pressure”. However, in a seminal work, Schoener (1979) showed theoretically that injury frequencies are not a function of the rate of such injury-producing events, but rather of the probability that such events are fatal. Here, this issue is revisited with a focus on ephemeral injuries, i.e. those that can heal completely and become unrecognizable, as is the case in many echinoderms. It is shown that for ephemeral injuries, the rate of injury-producing events can be reconstructed from injury frequencies if the time that it takes for an injury to heal is known.  Two examples from echinoderms are used to illustrate how injury frequencies can be converted to a rate of the injury-producing events and how higher frequencies of injury need not correspond to higher rates of such events.