Claire Corlett

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The Age Of Fishes

The Age Of Fishes

Ray-finned fishes are some of the most abundant and most diverse animals in the ocean today. But how did they get to that point? A new study from the Scripps Institution of Oceanography at UC San Diego might have some answers for us. Lead author Elizabeth Sibert tells us more: My name is Elizabeth Sibert and I am a PhD student here at the Scripps Institution of Oceanography. My research focuses on how ocean ecosystems have changed in the past, because by studying how ocean ecosystems have changed, we can understand how they will change in the future. My main tools for this research are called ichthyoliths. Literally, ichthyolith means “fish stone.” Ichthyoliths are fossil fish teeth and shark scales found in marine sediments all over the world. They’re so small that you need a microscope to see them, but in a piece of sediment about this big, I can find hundreds, if not thousands of ichthyoliths. In the Cretaceous, when dinosaurs roamed the land, the marine ecosystem was not that different from how it looks today. There were phytoplankton. And those phytoplankton were eaten by zooplankton. And in turn, those zooplankton are eaten fish and other critters, such as this ammonite. The top predators in the Cretaceous looked pretty similar to some top predators in our oceans today. We had sharks, for example. But we also had marine reptiles like mosasaurs. The Cretacous ocean was really a stable, happy place. Nothing major seems to changed in the last ten million years of the Cretaceous. However, when the asteroid hit, there was a huge change. The whole ecosystem turned inside out, and up on its head. A lot of phytoplankton and zooplankton species actually went completely extinct. In addition, larger consumers like ammonites completely disappeared. The mosasaurs and other marine reptiles were also vitims of the extinction. Despite the major destabilization at the base of the food web, fishes seemed to thrive. They increased in both absolute and relative abundance. It seems like the mass extinction was actually a really great thing for the ray-finned fishes. They took advantage of the destabilized ecosystem to explore roles previously held by animals that were victims of the extinction. So we’ve found using these tiny ichthyoliths that the mass extinction really changed how the ocean worked. The old ecosystem was knocked out and cleared the way for all the fishes we see dominating the ocean today. It marks the beginning of a modern ocean ecosystem, and perhaps even the beginning of a true Age of Fishes.

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