Morphology

MacNeil et al 2012

 Somniosus microcephalus is known by many names, including gurry shark, grey shark,  eqalussuaq, and (most commonly) the Greenland shark. They have thick, cylindrical, torpedo shaped bodies covered in tough dermal denticles. Specimens usually range in color from light brown with deeper brown mottling, to dark grey with nearly black spots ( MacNeil et al 2012).

  The Greenland shark is the largest fish known to inhabit arctic waters, and are usually between 3 and 5 meters long, with the largest reliably recorded shark weighing in at 1023 kg and measuring 640cm long (slightly longer than a Ford F150)( MacNeil et al 2012).

S.microcephalus is also the oldest living vertebrate. Due to their lack of calcified tissue the exact extent of the species longevity was not known until recently. In 2016 researchers utilized radiocarbon dating on the nuclei of individuals’ eye lenses. Doing this, it was determined that the oldest individual of those studied was  392 ± 120 years old. To put that in perspective, if that shark was the youngest predicted age it would have been born 147 years before the start of the American Revolution ( Nielsen et al 2016).

The Greenland shark is also thought to be viviparous, meaning it gives birth to fully formed young. This conclusion is based off of multiple accounts of pups found in utero, the lack of a shell gland or yolk sac (MacNiel et al 2012), and that several other Squaliformes also reproduce viviparously ( Wourm 1981).

Because of their long lifespans, using a standard DEB model it’s been proposed that that the Greenland shark likely doesn’t reach sexual maturity until 150 years old, and may have a gestation period of 8-18 years. A mother may potentially birth as many as 200-700 pups in her lifetime (Augustine et al 2017).