Cephalopod ancestors once had shells. When did they lose them?
With the molecular clock technique, which allowed him to use DNA to map out the evolutionary history of the cephalopods, he found that today’s cuttlefish, squids and octopuses began to appear 160 to 100 million years ago, during the so-called Mesozoic Marine Revolution.
During the revolution, underwater life underwent a rapid change, including a burst in fish diversity. Some predators became better suited for crushing shellfish, while some smaller fish became faster and more agile.
“There’s a continual arms race between the prey and the predators,” said Mr. Tanner. “The shells are getting smaller, and the squids are getting faster.”
The evolutionary pressures favored being nimble over being armored, and cephalopods started to lose their shells, according to Mr. Tanner. The adaptation allowed them to outcompete their shelled relatives for fast food, and they were able to better evade predators. They were also able to keep up with competitors seeking the same prey.
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This post first appeared on scheiner. Read the original article.