SCIENCE
Sharp-toothed giants of the ocean
Remarkably, there exists an animal species that has persisted since the dawn of the 1600s, a group of dark, slow-moving giants that live deep in the world’s coldest oceans and still grasp to life today.
The Greenland shark, also called Somniosus microcephalus, is now thought to be the longest living vertebrate on Earth. An international team of scientists, including ones from Scandinavia and Greenland, recently used radiocarbon dating of metabolically inactive eye lens tissue to show that the mysterious and poorly understood Greenland shark can live for more than four centuries. This is around twice the previous record of longevity in a vertebrate, which belonged to the Bowhead whale. What’s more, it is estimated that it takes 15 decades for the Greenland shark to reach sexual maturity, about
seven times the age when humans reach sexual maturity (20 years). Little is known about these sharp-toothed elders of the ocean, but the new findings have catapulted Greenland sharks into the mainstream and made them stars of the research world. It all started in 2010 when Professor John Steffensen, a marine biologist at the University of Copenhagen, and his graduate student, Julius Neilsen, spent three years sampling the sharks close to Greenland, trying to discern their age. Normally, the age of a fish can be determined by counting the layers of
A Greenland shark, thought to be the longest living vertebrate on Earth. © Paul Nicklen
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calcium carbonate in their ears, similar to dendrology (counting tree-rings). But Greenland sharks do not possess calcium in their ears, so the researchers turned to the sharks’ gray-black eyes—specifically the carbon dating of the proteins in the lenses of their eyes—to gauge the age of the great Somniosus microcephalus. Carbon dating has long been used to estimate lifespan. The technique is based on the fact that carbon-14, which is found in all living things, degrades over time at a known rate, meaning that the relative amount of C-14 within a specimen is reflected in its age. Of course, there is a degree
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