The first clue that the Greenland shark might be a living fossil came not from its massive size but from the chemistry locked inside its eyes. Scientists used radiocarbon dating on the protein crystals of eye‑lens nuclei, which do not remodel after birth, and discovered individuals that were over four centuries old—older than any other known vertebrate.
These sharks inhabit the icy waters of the North Atlantic and Arctic Ocean, often cruising at depths between 200 and 1,500 meters. The environment is perpetually cold, with temperatures hovering just above freezing. To thrive there, they have evolved a suite of cold adaptation mechanisms, including antifreeze glycoproteins that prevent ice crystal formation in their blood and tissues.
One of the most striking physiological traits is their slow metabolism. Unlike faster‑moving pelagic sharks, the Greenland shark moves languidly, conserving energy by maintaining a body temperature only slightly above that of the surrounding water. Their cartilage-rich skeleton and low muscle mass further reduce metabolic demands, allowing them to survive on infrequent meals such as carrion or slow‑swimming fish.
Reproduction in this species is equally enigmatic. Recent observations suggest an extraordinarily prolonged gestation period that may last up to 15 years, one of the longest known among vertebrates. Females give birth to a handful of relatively large pups, which explains why population recovery is so slow and why each individual carries immense evolutionary value.
The longevity record belongs to a specimen nicknamed “Mack,” whose eye‑lens analysis indicated an age of about 392 years, meaning it was born in the early 17th century. Such ages are possible because cellular damage accumulates at a glacial pace; their DNA repair systems appear highly efficient, and the cold environment slows oxidative processes that typically shorten lifespans in warmer waters.
Despite their resilience, Greenland sharks face growing threats. Climate change is altering sea‑ice patterns, potentially disrupting the prey base they rely on. Additionally, they are frequently caught as bycatch in longline fisheries targeting Arctic cod, and because they mature so slowly, even modest mortality rates can have outsized impacts on population stability.
Future research aims to illuminate the remaining mysteries of this ancient predator. Advances in satellite tagging now allow scientists to track deep diving movements over months, while genomic sequencing promises insights into the genetic basis of their longevity and cold tolerance. Each new discovery not only deepens our respect for the Greenland shark but also offers clues about how life can endure in Earth’s most extreme habitats.