SEAFOOD THROUGH TIME REVISITED: COUPLED BODY SIZE EVOLUTION, METABOLIC ACTIVITY, AND ECOLOGICAL DIVERSIFICATION IN PHANEROZOIC BILATERIAN MARINE ANIMALS

In his “Seafood through time” paper, Richard Bambach argued that the overall metabolic activity of marine animals in the oceans increased over the Phanerozoic. Bambach inferred this increase based on qualitative observations that animals have become larger, fleshier, and filled more energetically expensive regions of the marine ecospace since the Cambrian. Analysis of our newly compiled database of more than 17,000 marine animal genera provides comprehensive quantitative support for Bambach’s hypothesis. Our database shows an order of magnitude increase in the mean biovolume of marine animal genera over the Phanerozoic.

We used living analogues to calculate trends in mean metabolic rate across genera over Phanerozoic time. We find that the mean metabolic rate across marine animal genera increased several orders of magnitude during the Phanerozoic.

Finally, we have also coded the genera in our database within a three-dimensional ecospace that describes life mode (i.e., tiering, motility, feeding). Generally, we find a correlation between body size and life mode. Size increase occurs within all major life modes, but feeding is the most important ecological determinant of body size with active, predatory modes being larger than more passive feeding modes. In addition, the relationship between ecology and body size has varied over evolutionary time in some major clades, suggesting that studies focused exclusively on living taxa can arrive at vastly different conclusions than studies that also include their extinct relatives.

Together these size, metabolic, and ecologic data provide a rich, function-oriented view of the Phanerozoic history of marine life that complements rather than duplicates the patterns and processes captured by taxonomic diversity data. As animals became larger, they occupied more energetically demanding modes of life: sessile to fast-moving, surface dwelling to deeply burrowing, filter feeding to predation.