Caribbean Monk Seal

Caribbean monk seals had a relatively large, long, robust body, could grow to nearly 2.4 metres (8 ft) in length and weighed 170 to 270 kilograms (375 to 600 lb). While historical accounts suggested males were larger, modern research into the genus Neomonachus suggests females may have been the larger sex, similar to their closest relative, the Hawaiian monk seal. Like other monk seals, this species had a distinctive head and face. The head was rounded with an extended broad muzzle. The face had relatively large wide-spaced eyes, upward opening nostrils, and fairly big whisker pads with long light-colored and smooth whiskers. When compared to the body, the animal's foreflippers were relatively short with little claws and the hindflippers were slender. Their coloration was brownish and/or grayish, with the underside lighter than the dorsal area. Adults were darker than the more paler and yellowish younger seals. Caribbean monk seals were also known to have algae growing on their pelage, giving them a slightly greenish appearance, which is similar to Hawaiian monk seals.

Caribbean monk seals were found in warm temperate, subtropical and tropical waters of the Caribbean Sea, Gulf of Mexico, and the western Atlantic Ocean. They probably preferred to haul out at low sandy beaches above high tide on isolated and secluded atolls and islands, but occasionally would visit the mainland coasts and deeper waters offshore. This species may have fed in shallow lagoons and reefs.

Historical records show that this species may have "hauled out" at resting areas on land in large social groups, typically 20–40 animals, but sometimes up to 100 individuals, throughout its range. The groups may have been organised based on age and life stage differences. Their diet most likely consisted of fish and crustaceans. Like other true seals, the Caribbean monk seal was sluggish on land. Its lack of fear of humans, and an unaggressive, curious nature was taken advantage of by human hunters.

Reproduction and longevity. Caribbean monk seals had a long pupping season, which is typical for pinnipeds living in subtropical and tropical habitats. In Mexico, breeding season peaked in early December. Like other monk seals, this species had four retractable nipples for suckling their young. Newborn pups were probably about 1 metre (3 ft 3 in) in length and weighed 16 to 18 kilograms (35 to 40 lb) and reportedly had a sleek, black lanugo coat when born. It is believed this animal's average lifespan was approximately twenty years. The Caribbean monk seal nasal mite (Halarachne americana) was entirely dependent on the seal, living inside of its nasal cavity, and went extinct with it.