ESCALATION AND EXTINCTION SELECTIVITY: MORPHOLOGY VERSUS ISOTOPIC RECONSTRUCTION OF BIVALVE METABOLISM

Studies that have tested and failed to support the hypothesis that escalated species (e.g., those with predation-resistant adaptations) are more susceptible to elimination during mass extinctions have concentrated on the distribution and degree of morphological defenses in molluscan species. This mo...

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Bibliographic Details
Published in:Evolution 2002-02, Vol.56 (2), p.284-291
Main Authors: Dietl, Gregory P, Kelley, Patricia H, Barrick, Reese, Showers, William
Format: Article
Language:English
Subjects:
Animals
Biological Evolution
Burrowing
Escalation
Evolution
Extinct species
Extinction
extinction selectivity
Fossils
Geologic Sediments
Glossus markoei
Isotopes
Macrocallista marylandica
Maryland
Mass extinction events
Metabolism
Mollusca - anatomy & histology
Mollusca - classification
Mollusca - growth & development
Mollusca - metabolism
Mollusks
Oxygen Consumption
Predation
REGULAR ARTICLES
shell growth rates
Species extinction
Species Specificity
Taxa
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Summary:Studies that have tested and failed to support the hypothesis that escalated species (e.g., those with predation-resistant adaptations) are more susceptible to elimination during mass extinctions have concentrated on the distribution and degree of morphological defenses in molluscan species. This morphological approach to determining level of escalation in bivalves may be oversimplified because it does not account for metabolic rate, which is an important measure of escalation that is less readily accessible for fossils. Shell growth rates in living bivalves are positively correlated with metabolic rate and thus are potential indicators of level of escalation. To evaluate this approach, we used oxygen isotopes to reconstruct shell growth rates for two bivalve species (Macrocallista marylandica and Glossus markoei) from Miocene-aged sediments of Maryland. Although both species are classified as non-escalated based on morphology, the isotopic data indicate that M. marylandica was a faster-growing species with a higher metabolic rate and G. markoei was a slower-growing species with a lower metabolic rate. Based on these results, we predict that some morphologically non-escalated species in previous tests of extinction selectivity should be reclassified as escalated because of their fast shell growth rates (i.e., high metabolic rates). Studies that evaluate the level of escalation of a fauna should take into account the energetic physiology of taxa to avoid misleading results. Corresponding Editor: D. Geary
ISSN:0014-3820
1558-5646
DOI:10.1554/0014-3820(2002)056[0284:EAESMV]2.0.CO;2