Abstract

A combination of sclerochronologic techniques and stable isotope analysis reveals that the fossil bivalve Cucullaea raea, from the Eocene of Antarctica, regularly lived for more than a century. In addition, shell growth occurred only during the Austral winter, when food (phytoplankton) availability was limited by darkness. Although extreme longevity in modern bivalves tends to correlate with cold temperature, paleotemperature conversion of δ18O values indicates that these high-latitude fossil clams lived in relatively warm (∼14 °C) shallow seas of the Eocene greenhouse world. Growth cessation during otherwise optimal summer conditions is inferred to reflect summer spawning and a reproductive strategy by which to increase the likelihood of larval survival in a light-stressed (and hence food stressed) setting. Long life may therefore be adaptive in a setting where the chances of reproductive success during any one spawning cycle are very low. In addition, food limitation may play a role in extending life by reducing metabolic rate and somatic growth, slowing the process of senescence (aging). The unusual life history of this fossil high-latitude, temperate-water bivalve suggests that low light and food availability, as opposed to cold temperature, may have a greater influence on molluscan growth at high latitudes than previously thought.

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