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The sea mink (Neovison macrodon) is an extinct North American member of the family Mustelidae. It is the only mustelid, and one of only two terrestrial mammal species in the order Carnivora, to become extinct in historic times (the other being the Falkland Islands wolf). The body of the sea mink was significantly longer than that of the closely related American mink (N. vison), and also bulkier, leading to a pelt that was almost twice the size of the other species. The longest specimen recorded was said to be 82.6 cm (32.5 in). The sea mink produced a distinctive odor, and had fur that was said to be coarser and redder than the American mink's.
The sea mink was hunted to extinction before scientists had an opportunity to analyze them. From its relatives we have a general idea of what this semiaquatic weasel looked like. Accounts from locals to the New England/Atlantic Canadian regions say that the sea mink had a fatter body than that of the American mink. Furthermore, it had reddish-fur, and its tail was slightly[vague] bushy. This larger body and fur made it very profitable and desired to fur-trappers.
Similar to the European Mink and the American Mink, the sea mink’s diet consisted of seabirds, most likely the Labrador duck, seabird eggs, hard-bodied marine invertebrates, and in some cases insects. Since the sea mink was larger than the other two species of Mustelidae it is assumed that it ate in greater proportions.
The sea mink was the largest of the minks. Its skull had a wide rostrum, large opening of anterior nares, large antorbital foramina, and very large teeth. This species had a skull that was easily distinguishable from the other species of vison, American Mink, because of its large size and bigger teeth. Fur buyers and traders recognized the sea mink because of its larger size compared to other minks and eventually the species was exterminated by the interest in their fur.
Many skeletal remains of this mink have been found off the New England coast. The sea mink served as food for the Native American tribes that once lived there. These minks are described as large and heavily built, with a low sagittal crest and short, wide postorbital processes. Fragmentary skeletal remains of the sea mink leave most of its external measurements to speculation.
The sea mink was characterized by its solitary, territorial nature. Males were known to be particularly aggressive towards each other, marking territories with specific scents along a shoreline. In the event of trespassing, violent confrontations would occur. At the same time, males and females both lived promiscuous lifestyles, oftentimes mating with multiple partners especially during late spring, April to May timeframe.
The litter of pups, usually blind and helpless, were supported by the mother for a period of 13–14 weeks. However, many external threats affected the development of the baby pups, and high mortality rates were not uncommon.
Sea minks were semiaquatic animals that lived around the rocky coasts of New England and Atlantic Canada, as far north as Nova Scotia. They used to occupy rocky areas along the coastal lines. It inhabited the shores of New England and the Canadian Maritime Provinces until it was hunted to extinction in the 19th century. It was not a truly marine species, being confined to coastal waters. They also habituated near Casco Bay, Maine in the south to as far north as Newfoundland, Canada. The Labrador duck, with which it coexisted, may have been a prey item. 
The sea mink was the most aquatic member of Musteloidea except for the otters, and it was unusual in having rapidly evolved toward a marine habitat in the late Cenozoic. The sea mink family was originally from coastal Eastern North America, from Massachusetts to the Maritime Provinces. They had a more slender body than the American mink. It preferred coastal habitats, particularly rocky coasts and offshore islands.  
The sea mink was hunted to extinction to satisfy the demand of the European fur market. Fur traders made traps to catch the sea minks and also pursued them with dogs. Even before the European expansion, Native Americans would capture the animals for their pelts and flesh. A large contributing factor to the eventual extinction of the sea mink was the unregulated hunting and harvesting of these animals. Another possible contributing factor was the high mortality rate of the young. Ultimately, the sea mink became extinct sometime between 1860 and 1870. 
There has been a debate regarding whether the sea mink is a separate species from its relative the American mink or if it is a subspecies. Those that argue that the sea mink is a subspecies often refer to it as Neovison vison macrodon. However, research has been conducted in which they compared the teeth of the sea mink, dating back 5000 to 250 years ago, with 158 other mink species. It was concluded that there was a great difference in dental proportions between the N. macrodon and N. vison that ultimately supports the hypothesis that sea minks are different species from the American minks. The marine diet of the sea mink caused the divergence of these two species.
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