Pinnipedia

The pinnipeds (Pinnipedia) are a superfamily of carnivorous mammals of the suborder Caniformia; along with cetaceans, and sirenians, the only mammals adapted to marine aquatic life. They have an elongated and spindle-shaped body, short legs with webbed, fin-shaped extremities. They are usually gregarious, feeding on fish, molluscs and crustaceans. They are present in all seas except the Caribbean Sea, where an already extinct species abounded: the Caribbean monk seal, which probably became extinct in the middle of the century XX. They are divided into three families, the otariids (bears, wolves and sea lions), the phocids (seals) and the odobenids (walruses).

The largest pinniped is the sea elephant, from the Phocidae family, which can measure up to 7 meters.

Seals range in size from the 1 m (1.1 yd) 45 kg (99.2 lb) Baikal seal to the 5 m (5.5 yd) 3,200 kg (7,054.8 lb) male) male southern elephant seal, which is also the largest member of the order Carnivora. Several species exhibit sexual dimorphism. They have streamlined bodies and four limbs modified into fins. Although they are not as fast in the water as dolphins, seals are more flexible and agile. Otariids use their forelimbs mainly to propel themselves in the water, while phocids and walruses use their hindlimbs. Otariids and walruses have hind limbs that can be dragged under the body and used as feet on land. By comparison, phocid terrestrial locomotion is more cumbersome. Otariids have visible external ears, while phocids and walruses lack them. Pinnipeds have well-developed senses: their sight and hearing are adapted to both air and water, and they have an advanced tactile system in their whiskers, or vibrissae. Some species are well adapted for diving to great depths. They have a layer of fat under the skin to keep them warm in cold water and, except for the walrus, all species are covered in hair.

Although pinnipeds are widespread, most species prefer the cooler waters of the northern and southern hemispheres. They spend most of their lives in the water, but come ashore to mate, give birth, shed their skin, or escape predators such as sharks and killer whales. Seals primarily live in marine environments but can also be found in fresh water. They feed mainly on fish and marine invertebrates; some, like the leopard seal, feed on large vertebrates, such as penguins and other seals. Walruses are specialized in feeding on bottom-dwelling mollusks. Male pinnipeds often mate with more than one female (polygyny), although the degree of polygyny varies by species. Males of land-breeding species tend to mate with greater numbers of females than males of ice-breeding species. Male pinniped strategies for reproductive success vary between defending females, defending territories that attract females, and performing courtship displays or lek mating. The young are usually born in the spring and summer months and the females assume almost all responsibility for their upbringing. The mothers of some species fast and nurse their young for a relatively short period of time, while others make foraging trips at sea between nursing sessions. Walruses have been known to nurse their young while at sea. Seals produce a number of vocalizations, most notably the barks of California sea lions, the gong-like calls of walruses, and the complex songs of Weddell seals.

The meat, fat, and skins of pinnipeds have traditionally been used by indigenous peoples of the Arctic. Seals have been depicted in various cultures around the world. It is common to keep them in captivity and sometimes they are even trained to perform tricks and tasks. Once relentlessly hunted by commercial industries for their products, seals and walruses are now protected under international law. The Japanese sea lion and Caribbean monk seal have gone extinct in the last century, while the Mediterranean monk seal and Hawaiian monk seal are listed as endangered by the International Union for Conservation of Nature. In addition to hunting, pinnipeds also face threats from accidental trapping, marine pollution, and conflicts with the local population.

Description

The auditory pavilion is absent or very small (otariids). The eyes are adapted to vision under water. Thin coat. They have a fatty layer under the skin, with functions of thermal insulation, energy reserve and flotation.

The teeth are usually small except for the walrus and leopard seal which have larger ones, more for digging in the bottom than for defense. The breathing apparatus is adapted for prolonged immersion.

Unlike cetaceans, they can move on land, albeit clumsily. They can only give birth on land. A calf is usually born at birth, which is cared for by the mother for four to five months, after which the young calf is left alone to fend for itself.

Anatomy and Physiology

Pinnipeds have streamlined, spindle-shaped bodies with reduced or no external ear flaps, rounded heads, flexible necks, limbs modified into fins, and small tails. Pinniped skulls have large eye sockets, short snouts, and a constricted interorbital region.. They are unique among carnivores in that their orbital walls are formed for the most part by the maxilla, which is not contained by certain facial bones. Compared to other carnivores, their teeth tend to be fewer in number (especially incisors and rear molars), pointed and cone-shaped, and lack carnassials. The walrus has unique upper canines that elongate into fangs. mammary glands and genitalia of pinnipeds can be retracted into the body.

Pinnipeds range in size from 1 m and 45 kg in the Baikal seal to 5 m and 3200 kg in the southern elephant seal. In general, they tend to be larger than other carnivores; the southern elephant seal is the largest carnivore. Several species have male-biased sexual dimorphism that correlates with the degree of polygyny in a species: highly polygynous species such as elephant seals are extremely sexually dimorphic, while less polygynous species Polygynous have males and females that are closer in size. In lobodont seals, the females are slightly larger than the males. Males of sexually dimorphic species also tend to have secondary sexual characteristics, such as the prominent proboscis of elephant seals, the inflatable red nasal membrane of hooded seals, and the thick necks and manes of otariids. Despite the correlation between size dimorphism and the degree of polygyny, some evidence suggests that size differences between the sexes arose due to ecological differences and before the development of polygyny.

Males and females of South American sea lions, showing sexual dimorphism.

Almost all pinnipeds have fur, with the exception of the walrus, which is only sparsely covered. Even some species with full fur (notably sea lions) have less fur than most land mammals. In species that live on ice, pups have thicker fur than adults. The individual hairs of the coat, collectively known as lanugo, can trap heat from sunlight and keep the pup warm. Pinnipeds are typically countershaded, possessing a darker colored back and a lighter colored belly, which It is used to remove shadows caused by light shining on ocean water. The pure white fur of harp seal pups conceals them in their arctic environment. Some species, such as ribbon seals, ringed seals, and leopard seals, have contrasting patterns of light and dark coloration. All species with full fur molt; phocids shed once a year, while otariids shed gradually year-round. Seals have a layer of subcutaneous fat that is especially thick in phocids and walruses. The blubber serves both to keep the animals warm enough to provide them with energy and nourishment when they are fasting. It can constitute up to 50% of the body weight of a pinniped. Young are born with a thin layer of blubber, but some species make up for this with thick lanugos.

Pinnipeds have a simple stomach similar in structure to terrestrial carnivores. Most species do not have a cecum or a clear demarcation between the small and large intestine; the large intestine is comparatively short and only slightly wider than the small intestine. The length of the small intestine varies between 8 times (California sea lion) and 25 times (elephant seal) the length of the body. The length of the intestine may be an adaptation to frequent deep dives, as the increased volume of the digestive tract serves as an expanded storage compartment for partially digested food during the dive. Pinnipeds do not have an appendix. As in most marine mammals, the kidneys are divided into small lobes and can effectively absorb water and filter excess salt.

Locomotion

Port seal (up) and California sea lion swimming. The first thing with its rear fins and the second with the fronts.

Pinnipeds have two pairs of fins in front and behind, the front and the rear. The elbows and ankles are encased in the body. Pinnipeds tend to be slower swimmers than cetaceans, typically swimming at a speed of 5–15 knots compared to around 20 knots for various dolphin species. Seals are more agile and flexible, and some otariids, such as the California sea lion, are able to bend their necks back far enough to reach their hind flippers, allowing them to perform dorsal gyrations. Pinnipeds have several adaptations to reduce drag. In addition to their streamlined bodies, they have smooth networks of muscle bundles on their skin that can increase laminar flow and make it easier for them to glide through the water. They also lack arrector pili, so their fur can be streamlined while swimming.

When swimming, otariids rely on their foreflippers for locomotion similar to penguins and sea turtles. Foreflipper movement is not continuous, and the animal glides between strokes. Compared to terrestrial carnivores, the forelimbs of otariids are of reduced length, giving the locomotor muscles of the shoulder and elbow joints a greater mechanical advantage; the hind flippers serve as stabilizers. Phocids and walruses swim by moving their hind flippers and lower bodies from side to side, while their front flippers are used primarily for steering. Some species rise out of the water, which may allow them to travel faster. Additionally, sea lions have been known to "ride" above the waves, which probably helps them decrease their energy consumption.

Pinnipeds can move on land, though not as well as land animals. Otariids and walruses are able to rotate their hind flippers forward and under their bodies in order to "walk" on all fours. The front flippers move in a transverse, rather than a sagittal. Otariids rely on head and neck movements rather than hind flippers for terrestrial locomotion. By swinging their heads and necks, otariids create momentum as they move. Sea lions have been recorded climbing flights of stairs. Phocidae are less agile on land. They cannot pull their hind flippers forward, and move on land by lurching, bouncing, and waddling while their front flippers keep them balanced. Some species use their front flippers to propel themselves. Land locomotion is easier for phocids on ice, as they can sledge.

Senses

Light reflection in a marine elephant eye

The eyes of pinnipeds are relatively large for their size and are located near the front of the head. An exception is the walrus, whose smaller eyes are located on the sides of the head. This is because it feeds on immobile bottom-dwelling molluscs and therefore does not require keen vision. A seal is adapted to see both underwater and in the air. The lens is mostly spherical, and much of the retina is equidistant from the center of the lens. The cornea has a flattened center where refraction is almost the same in both water and air. Pinnipeds also have a highly muscular and vascularized iris. The well-developed dilator muscle gives animals a great range in pupil dilation. When contracted, the pupil is usually pear-shaped, although that of the bearded seal is more diagonal. In species that live in shallow water, such as harbor seals and California sea lions, dilation varies little, while deep-diving elephant seals have much greater variation.

Front view of the head of a brown fur seal.

On land, pinnipeds are closely watched in dim light. This is reduced in bright light, as the retracted pupil reduces the ability of the lens and cornea to deflect light. They also have a well-developed tapetum lucidum, a reflective layer that increases sensitivity by reflecting light through the rods. This helps them see in low light conditions. Seals that live on ice, such as the harp seal, have corneas that can tolerate the high levels of ultraviolet radiation typical of bright, snowy environments. As a result, they do not suffer from snow blindness. Pinnipeds appear to have limited color vision, lacking S-cone cells. Flexible eye movement has been documented in seals. Walrus extraocular muscles are fine. developed. This and their lack of an orbital roof allow their eyes to bulge and see both frontally and dorsally. Seals release large amounts of mucus to protect their eyes. The corneal epithelium is keratinized and the sclera is thick enough to support diving pressures. As in many mammals and birds, pinnipeds have nictitating membranes.

Pinniped hearing is adapted to hearing underwater, where it can hear sound frequencies up to 70,000 Hz. In air, hearing is somewhat reduced in pinnipeds compared to many land mammals. Although they are capable of hearing a wide range of frequencies (for example, 500 to 32,000 Hz in northern fur seals, compared to 20 to 20,000 Hz in humans), their hearing sensitivity in air is generally weaker. A study of three species—the harbor seal, the California sea lion, and the northern elephant seal—found that the sea lion was better adapted for hearing in air, the harbor seal being equally capable of hearing in air and in the water, and the elephant seal was better adapted for hearing underwater. Although pinnipeds have a fairly good sense of smell on land, it is useless underwater as their nostrils are closed.

Vibrissae de morsa

Pinnipeds have a well-developed sense of touch. Their vibrissae have ten times more innervation than terrestrial mammals, allowing them to effectively detect vibrations in water. These vibrations are generated, for example, when a fish swims through the water. Sensing vibrations is useful when animals are foraging for food and can supplement or even replace vision, especially in the dark. Harbor seals have been observed to follow the variable paths of another seal that swam ahead for several minutes. before, similar to a dog following a scent trail, and even discriminating the species and size of the fish responsible for the scent. Blind ringed seals have even been observed hunting successfully on their own in Lake Saimaa, probably relying on their vibrissae for sensory information and to capture prey.

Unlike land mammals such as rodents, pinnipeds do not move their whiskers over an object when examining it, but rather extend their movable whiskers and hold them in the same position. By keeping their vibrissae stationary, pinnipeds are able to maximize their detection ability. Phocid vibrissae are wavy and wavy while those of otariids and walruses are smooth. Research is underway to determine the function, if there is, of these forms in the detection capacity. However, the angle of the vibrissae with respect to the current, and not the shape, seems to be the most important factor. The vibrissae of some otariids are quite long; those of the Antarctic fur seal can reach 41 cm. Walruses have the most vibrissae, with 600-700 individual hairs. They are important for detecting their prey on the muddy seabed. In addition to foraging, vibrissae may also play a role in navigation; spotted seals seem to use them to detect breathing holes in the ice.

Scuba Diving Adaptations

Weddell Foca submerged.

Before diving, pinnipeds typically exhale to empty their lungs of half the air, and then close their nostrils and throat cartilage to protect the trachea. Their unique lungs have heavily reinforced airways with rings of cartilage and smooth muscle, and alveoli that completely deflate during the deepest dives. While land mammals generally cannot empty their lungs, pinnipeds can reinflate their lungs even after complete respiratory collapse. The middle ear contains sinuses that probably fill with blood during dives, preventing ear compression. medium. The heart of a seal is moderately flattened to allow the lungs to deflate. The trachea is flexible enough to collapse under pressure. During deep dives, the air remaining in their bodies is stored in the bronchioles and trachea, preventing them from experiencing decompression sickness, oxygen toxicity, and narcosis. of nitrogen. Additionally, seals can tolerate large amounts of lactic acid, which reduces skeletal muscle fatigue during intense physical activity.

The main adaptations of the circulatory system of pinnipeds for diving are the enlargement and greater complexity of the veins to increase their capacity. Retia mirabilia form blocks of tissue on the inner wall of the thoracic cavity and the periphery of the body. Containing extensive convoluted coils of thin-walled arteries and veins, these masses of tissue act as reservoirs of blood that increase reserves of oxygen for use during diving. Like other diving mammals, pinnipeds have large amounts of oxygen. hemoglobin and myoglobin stored in your blood and muscles. This allows them to stay submerged for long periods of time while still having enough oxygen. Deep-diving species, such as elephant seals, have a blood volume that accounts for up to 20% of their body weight. When they dive, they slow their heart rate and maintain blood flow only to the heart, brain, and lungs. To keep their blood pressure stable, phocids have an elastic aorta that dissipates some of the energy of each heartbeat.

Thermoregulation

North sea elephant resting in the water

Pinnipeds conserve heat through their large, compact body size, insulating fat and fur, and high metabolism. In addition, the blood vessels in their fins are adapted for countercurrent exchange. Veins containing cold blood from the extremities of the body surround arteries, which contain warm blood received from the core of the body. Heat from the arterial blood is transferred to the blood vessels, which then recirculate the blood back to the core. The same adaptations that conserve heat while in water tend to inhibit heat loss when out of water. To counteract overheating, many species cool themselves by throwing sand on their backs, adding a layer of cool, moist sand that increases heat loss. Northern fur seals pant to help keep cool, while monk seals often dig holes in the sand to expose cooler layers for resting.

Sleep

Pinnipeds spend many months at a time in the sea, so they must sleep in the water. Scientists have recorded them sleeping for minutes while slowly moving down with their bellies up. Like other marine mammals, seals sleep in the water with half their brains awake so they can detect and escape predators. When sleeping on land, both sides of their brain go into sleep mode.

Families

Pinnipeds are divided into three extant families and two extinct families:

• Otariidae, with auditory pavilion; later forward-directed limbs, functional in terrestrial displacement. Examples: sea lions, sea lions and sea bears.
• Phocidae, without auditory pavilion; later backward and non-functional extremities in terrestrial displacement. More known for seals.
• Odobenidae, without auditory pavilion; later forward-directed limbs, functional in terrestrial displacement, rough skin and with long fangs. The only non-extinct species is the morsa (Odobenus rosmarus).
• Desmatophocidae †, extinct miocene pinnips, as Desmatophoca.
• Enaliarctidae †, fossil genders Enaliarctos and Pacific belong to this family.

Classification score

Pinnipeds were once classified in a separate order from carnivores. But various studies indicate that they share many similarities with them and have been included in this group.