LATITUDINAL PATTERNS IN LIFESPAN AND GROWTH RATE OF PLIOCENE GLYCYMERIS SUBOVATA

Marine bivalves are some of the longest living non-colonial animals on the planet today, reaching lifespans in excess of 500 years. Recent work on modern bivalves documented a latitudinal pattern in lifespan and growth rate as measured by the von Bertalanffy growth parameter, k. Species from higher latitudes have lower k-values and longer lifespans, whereas species from low latitudes have higher k values and shorter lifespans. Such a strong latitudinal pattern across groups of modern marine bivalves suggest an environmental factor related to latitude (such as temperature) is responsible for the pattern. If true, we hypothesize that similar patterns occurred in the past. Despite much work on lifespans of modern bivalves, little is known about the life histories of fossil bivalves. Here, we examine annual growth lines in the hinge of Pliocene Glycymeris subovata from four US Atlantic Coastal Plain sites to determine if similar latitudinal patterns existed in the past. Our results show a similar pattern of decreasing k values with latitude but no real trend in lifespan with latitude. Climate during the Pliocene was warmer than what we see today, yet a similar pattern is seen in both modern and Pliocene bivalves. Thus, our findings suggest that there are more factors other than temperature affecting the growth rate and lifespan of bivalves.