The Ancient Hot Air Balloons of the Ocean
520 million years ago, the world's first superpredator, Anomalocaris, appeared in the Cambrian oceans. This creature, who's name means "weird shrimp" looked a little strange with long front appendages and undulating flaps over its body, but its hunting prowess was no joke. The creature could swim up and down, a new development in the biological arms race, and struck at bottom feeders from above. Such a move literally blindsided many creatures; they hadn't yet evolved eyes that could look up. Without any defenses, the early Cambrian was a buffet for Anomalocaris. New species had to evolve and fast if they wanted to keep pace with the sudden shift in predatory power.
Above: A model of Anomalocaris
Some creatures grew bigger or faster, others developed hard shells and spines, but the first cephalopods chose to follow in their predators foot steps and take to the new vertical dimension. It wouldn't be easy; their ancestors carried heavy shells made of calcium carbonate that could weigh them down. To get around this, the early cephalopods exploited physics to their advantage.
By sectioning their shells off in sealed chambers, they could create hollow parts of their shell. A tube appendage called "siphuncle" ran through these chambers, diffusing and pumping the seawater out of the shell. Left behind was a light gas which caused the creature's shell to become buoyant, just like a hot air balloon! The most amazing part is that the water expelled from their shells allowed these cephalodpods to jet around the ocean, meaning the action propelled them up and away at the same time in a beautiful synthesis of evolution.
The amazing shells are all we have left to study the early cephalopods, as their soft bodies aren't easy to fossilize. However, if you find an ammonite shell that's split open, you can actually see the chambering at work! Take a look at those beautiful and natural logarithmic spirals!