|The true seals or earless seals are one of the three main groups of mammals within the seal suborder, Pinnipedia. All true seals are members of the family Phocidae. They are sometimes called crawling seals, to distinguish them from the fur seals and sea lions of family Otariidae.
Phocids are the more highly specialized for aquatic life of the two groups and, unlike otariids, lack external ears and cannot bring their hind flippers under their body to walk on them.
They are more streamlined than fur seals and sea lions, and can therefore swim more effectively over long distances than those can. However, because they cannot turn their hind flippers downward, they are very clumsy on land, having to wriggle with their front flippers and abdominal muscles; this method of locomotion is called galumphing.
Additionally, true seals do not communicate by "barking" like the fur seals and sea lions of family Otariidae. They communicate by slapping the water and grunting.
Feeding and reproduction
Because a phocid mother's feeding grounds are often hundreds of kilometers from the breeding site, this means that she must fast while she is lactating. This combination of fasting with lactation is one of the most unusual and extraordinary behaviors displayed by the Phocidae, because it requires the mother seal to provide large amounts of energy to her pup at a time when she herself is taking in no food (and often, no water) to replenish her stores. Because they must continue to burn fat reserves to supply their own metabolic needs while they are feeding their pups, phocid seals have developed an extremely thick, fat-rich milk that allows them to provide their pups with a large amount of energy in as small a period of time as possible. This allows the mother seal to maximize the efficiency of her energy transfer to the pup and then quickly return to sea to replenish her reserves. The length of lactation in phocids ranges from 28 days in the Northern Elephant Seal to just 3-5 days in the Hooded Seal. The nursing period is ended by the mother, who departs to sea and leaves her pup at the breeding site. Pups will continue to nurse if given the opportunity, and "milk stealers" that suckle from unrelated, sleeping females are not uncommon; this often results in the death of the pup whose mother the milk was stolen from, as any single female can only produce enough milk to provision one pup.
The pup's diet is so high-calorie that the pup builds up a large store of fat. Before the pup is ready to forage on its own, the mother abandons it, and it lives on its fat for weeks or months while it develops independence. Seals, like all marine mammals, need time to develop the oxygen stores, swimming muscles and neural pathways necessary for effective diving and foraging. Seal pups typically eat no food and drink no water during the fast, although some polar species have been observed to eat snow. The postweaning fast ranges from 2 weeks in the Hooded Seal to 9-12 weeks in the Northern Elephant Seal. The physiological and behavioral adaptations that allow phocid pups to endure these remarkable fasts, which are among the longest for any mammal, remain an area of active study and research.
Compared to most phocids Leopard Seals are highly evolved for their role as keystone predator. Although they are true seals and swim with their hind limbs, they have powerful highly developed forelimbs similar to a sea lion, giving them a maneuverability similar to Otariidae such as sea lion and fur seals. A classic example of convergent evolution. Like these eared seals, Leopard seals are shallow water hunters, and do not dive deep like the other seals of the antarctic Weddell seals, Ross seals and Elephant seals, which can all dive to several hundred meters in search of squid. Leopard seals have unusually loose jaws that can open more than 160 degrees allowing them to bite larger prey. Their heads also are more similar to that of a mammal-like "reptile" than that of a mammal.
Like most carnivores, their front teeth are sharp, but their molars lock together in a way that allows them to sieve krill from the water, similar to crabeater seals. Their senses of eyesight and smell are highly developed. These senses, coupled with streamlined bodies that enable the seals to move swiftly through the water, ensure that they are formidable predators.
Leopard seals are solitary creatures and come together in small groups only when it is time to mate. The female digs a hole in the ice and after a nine months gestation the female gives birth to a single pup during the Antarctic summer. She protects the pup until it is able to fend for itself.
Leopard seals are bold, powerful and curious. In the water, there is a fine line between curiosity and predatory behavior, and they may 'play' with penguins that they do not intend to eat.
When hunting penguins, the Leopard Seal patrols the waters near the edges of the ice, almost completely submerged, waiting for the birds to enter the ocean. It kills the swimming bird by grabbing the feet, then shaking the penguin vigorously and beating its body against the surface of the water repeatedly until the penguin is dead. Previous reports have said that Leopard seals skin their prey has been proved incorrect. Lacking the teeth necessary to slice their prey into manageable pieces, they flail their prey from side to side in order to tear and rip it into smaller pieces.
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