In the span of a few hundred million years, sharks 🦈 have gone from anchovy-sized body feeders to giants measuring up to 20 meters long, by some estimates.
But were sharks always this diverse? What were the earliest sharks like, and when did some sharks come to dominate the marine food chain?It depends on how far you want to go back of course, but some researchers now believe that the group that includes all three living groups of sharks — rays, sharks and chimeras — evolved first from the acanthodians.“They are all terribly spiny and small,” says Michael Coates, a biologist at the University of Chicago.
Most acanthodians were fingerling-sized — just anchovies in size. They were likely among the first fishes that moved off the seafloor into the water area during the so-called nekton revolution in the Silurian and Devonian periods. While modern ghost sharks are mostly relegated to the depths of the ocean, the order was all over the place back then, with some species even spending time in brackish water, rather than seawater.The earliest elasmobranchs — sharks and rays — also began to adopt sophisticated feeding techniques. Some dating to roughly 340 million years ago had developed the ability to suction feed rather than just engulf food with their jaw, similar to modern nurse sharks.
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