Long before the first dinosaurs roamed the earth, the oceans were full of creatures known as ammunition. Scientists have now created several types of robotic projectiles, to see how the different shell shapes they evolved affect their movement through the water.
Ammo belongs to the cephalopod group of marine invertebrates, whose current members include octopuses, squid, and cuttlefish. Unlike those examples, however, bullets have protective outer shells – and those shells do not maintain a consistent shape throughout the fossil record.
Led by postdoctoral fellows David Peterman and Asst. Professor Kathleen Ritterbush, a research team at the University of Utah recently set out to determine how different shell shapes affect animal locomotion. To do so, the scientists created a free-swimming robotic bullet.
Each consists of a 3D-printed polymer shell with a watertight internal cavity, inside which are electronics including a battery, a microcontroller, a motor, and a propeller-powered water pump. There are also air-filled voids and counterweights, to reproduce the weight distribution of the existing nautilus – it is the only cephalopod today with a shell.
Moreover, the robots are very popular. This means that when placed in water, they neither sink to the bottom nor float to the surface.
Their shell shape includes that of a snake, combining tight helixes with a narrow shell; a sphaerocone, with several thick helices and a broader, almost spherical shell; and somewhere in the middle of oxycone, combining thick helixes with a narrow, streamlined shell.
Initially, each model was placed in an underwater grip in a pool, then released so it could fly through the water. As it did so, its movements and position in three dimensions were recorded by an underwater video camera. Each model does about a dozen individual runs.
When analyzing the footage, it was found that each shape had its own strengths and weaknesses. For example, narrower housings create less drag and are more stable when traveling straight through the water. The wider shells, while making it move more slowly, with less energy, could change direction more easily – a trait that may have made it possible for projectiles to catch prey or escape predators. .
“These results reiterate that there is no single optimal shell shape,” says Peterman. “Natural selection is a dynamic process that changes over time and involves many functional trade-offs and other constraints. The exoskeleton cephalopod is the perfect target for studying these dynamics. complex because of their enormous time range, ecological significance, abundance, and high rate of evolution.”
An article on the research was recently published in the journal Scientific reports.
Source: University of Utah