Earless seal

Lore & Background

The earliest known fossil earless seal is Noriphoca gaudini from the late Oligocene or earliest Miocene of Italy. Other early fossil phocids date from the mid-Miocene, 15 million years ago in the north Atlantic. Until recently, many researchers believed that phocids evolved separately from otariids and odobenids, and that they evolved from otter-like animals such as Potamotherium. Recent evidence strongly suggests a monophyletic origin for all pinnipeds from a single ancestor, possibly Enaliarctos, most closely related to the mustelids and bears. Monk seals and elephant seals were previously believed to have first entered the Pacific through open straits between North and South America, but it is now thought that the monk seals, elephant seals, and Antarctic seals all evolved in the southern hemisphere and likely dispersed to their current distributions from more southern latitudes.

Reader's Guide

Earless seals represent a major evolutionary branch of pinnipeds, distinguished from fur seals and sea lions by their lack of external ears, bound hind flippers, and specialized aquatic adaptations. Their streamlined bodies and efficient swimming allow them to forage far from land, exploiting prey resources that otariids cannot reach. Phocids have fewer teeth than land-based carnivores, and some species lack molars altogether. Their respiratory and circulatory systems are adapted to facilitate deep diving, with air forced from the lungs into upper passages to prevent the bends. Phocids produce thick, fat-rich milk that allows mothers to nurse pups quickly while fasting, with lactation ranging from three to five days in the hooded seal to five to seven weeks in the monk seal. The postweaning fast, during which pups consume their own fat stores, can last up to 9–12 weeks in the northern elephant seal. Phocids use at least four feeding strategies—suction feeding, grip-and-tear feeding, filter feeding, and pierce feeding—and most are opportunistic, employing multiple strategies. Their communication differs from otariids: phocine seals do not bark but slap water and grunt, while monachine seals like elephant seals and Weddell seals are known for vocalizing. The Baikal seal is the only exclusively freshwater seal species.

Did You Know?

• The Baikal seal is the only species of exclusively freshwater seal.
• Phocids have fewer teeth than land-based members of the Carnivora, and some species lack molars altogether.
• Lactation in the hooded seal lasts only three to five days, one of the shortest among mammals.
• Phocids are known to deliberately nurse young that are not their own, a behavior that can lead to 'super weaners'.