In the process of learning that devil rays regularly make these dramatic dives, scientists may have solved an anatomical mystery as well: the purpose of the ray’s rete mirabile, a mass of blood vessels in the front of its skull that keep its brain warm. Simon Thorrold of Woods Hole Oceanographic Institution and his team put satellite tags on 15 Chilean devil rays, and tracked their movement for several months. In addition to recording their surface migrations across the tropical and subtropical North Atlantic Ocean, the tags documented the rays diving deep into the ocean’s bathyal zone. Water temperatures at this depth are below 39 degrees Fahrenheit. While more data are needed, the researchers say it’s likely the rays were hunting and feeding on tasty small fish—an active behavior that would require a well-warmed brain to do well. Before this study, “[I]t was a mystery as to why they had this system, which is a way of keeping brain activity high, even in a cold environment,” Thorrold told BBC News. “We looked at the data and of course, it made complete sense” that the ret__ia__ mirabil__ia helps the rays remain alert and efficient as they feed in the cold deep waters. Read the study, which has just been published in open format by the journal Nature Communications–no subscription required to enjoy the science.
