Marine Mammals
Anyone who has ever witnessed the early morning feeding at sea on a calm day has also seen the superiority of the warm-blooded physiology over the cold-blooded way of life. While the sardines, anchovies and other schooling fry are chased around by faster fish, sea birds, like dive bombers take their share of the feast. But even the predators, bonitos and bass, are easy prey for the second circle of divers, the dolphins. Sharks roam farther away to scoop up remains but don't venture in too close because of the dolphins...from the air and from below, the fish are no match for the warm-blooded birds and mammals.
The warmer the blood the higher the efficiency of the living thermodynamic machine. Birds and sea mammals have acquired their power while evolving out of the oceans; their physiology has coped with such problems as keeping their central temperature constant or holding their breath during deep, prolonged dives. The heat exchanging system present in their flukes, fins, wings, or webbed feet is ingenious. Some powerful fish, tuna, have also developed this system but this is only to keep their muscles a few degrees warmer than the surrounding water while the marine mammal and bird must keep their temperature constant whatever outside polar or tropic temperatures may be.
The warm blooded animals have no feeding problem. They have to eat a lot more compared to the same size fish. Colonies of millions of seabirds pile up on islands, feeding twice a day in less than half an hour and gorging themselves to a point of hardly being able to fly. In the sea, whales fill up on crustaceans in a few daily dives, pilot whales dive deep and fill up on squid or cuttlefish, and porpoises and dolphins and sea lions spend less than an hour a day to quench their appetite.
Having no difficulty in finding food, these warm blooded animals have lots of leisure time, explaining why they play, travel for no apparent reason and some, like the sea elephant, are so fat that they can afford to fast for several months when they come ashore to breed.
Leisure time has been used by the sea mammals that have a large brain to develop wit, intelligence, communication, and even some unnecessary feelings such as faithfulness, tenderness, and friendship.
This warm-blooded superiority has some severe limitations. Because of the high combustion of the excess food, excess oxygen is also needed (from the air) and this limits the duration of their dives. Some birds and cetaceans have modified their organs to perform dives of extended duration.
No birds, except the penguin, is at home in the sea like the pelagic mammals but many spend their life at sea except form that one short period of the year when they come ashore to mate, nest and raise their young. Whalebirds, prions, sea hawks, jaegers, and the albatrosses and shearwaters are among these pelagic birds. Other birds live in open waters just offshore, coming ashore little more than pelagic birds but remaining closer to land. (sea ducks) and some remain close to shore and seek haven in stormy weather on land or in shoreside ponds. (gulls terns, skimmers.)
The largest group of marine mammals are the Cetaceans. There are over 90 species. These have the most complex transition to marine life.
Cetaceans are shaped like fish but are not fish. There are 90 different species . They are all marine except a few freshwater dolphins. They are all totally dependent on support afforded by the water and can't survive on land. The whales, dolphins and porpoises are born live, suckle their young, and breath air. From the 4 ft. harbour porpoise to the 110ft blue whale these mammals have no need to come on to land. They have a pair of front flippers, but the rear limbs have disappeared and though there are rear limbs present in the embryo, they are small useless bones in the adult. There is a dorsal fin and the tail ends in a pair of fin like horizontal flukes. Blubber provides insulation and buoyancy and body hair is almost absent. The nostrils form a single or double opening called a blow hole on the head
There are two sub-orders...Odontoceti (toothed whales) equipped with pegshaped, spadelike teeth for grasping food, using biosonar or echolocation to locate prey at great depths (sperm whale) and include toothed whales, dolphins, porpoises and killer whales.
The second sub-order is Mysticeti (mustache G) or toothless baleen whales which scoop up minute plankton and small drifting fish with overlapping flaps of baleen (made of similar material as your hair and nails. They feed by taking in a big mouthful of water, squeezing it through the bristles and licking the food left behind. Included are the blue whale and divide into three families; rorqual whales...blue, humpback, fin, sei, Byrds and minke which feed on dense swarms of krill, 2. Right whales inc. black, Greenland, pygmy which feed on swarms of Copepods and the 3. gray whale which feed on worms, small crustaceans and other bottom organisms by sucking up sediments and filtering its food from the mud.
Pinnipeds, seals, sea lions and walruses while they need to come ashore to breed, they go to sea only to feed. They evolved from early forms of terrestrial carnivores/cats,dogs,bears and they are all predators. They also have blubber which acts as insulation, food reserve, and buoyancy. There are 19 species of seals, distinguished by having rear flippers that cannot move forward. On the land they pull themselves forward with their front flippers. Elephant seals are the largest with males reaching up to 20' in length. Monk seals live in warm regions, the exception to the relatively cooler regions where seals inhabit.
Sea lions or eared seals are similar to seals except they have external ears and can move their rear flippers forward so they can use all 4 limbs to walk or run on land. The head of the sea lions look doglike while the seals look more like a cat. There are 5 species of sea lions and 9 related fur seals.
Walrus is a large pinniped with a pair of distinctive tusks protruding down from the mouth. It feeds mostly on invertebrates, clams but there is no evidence that the tusks are used to dig up the clams and they travel along the bottom sucking up their food, with their stiff whiskers acting as feelers.
Sea otters, the member of Carnivora, the smallest of the marine mammals. They lack blubber and their fur traps air there to act as a layer of insulation.
Sirenia- dugongs and manatees, descendants from elephants, sluggish, with forearms modified as flippers and no hind limbs, may have been the source of the mermaid legend, thus the name Sirenia ( sailors probably had been at sea too long)
Adaptations;
Streamlining..in the evolutionary process of streamlining the shape, cetaceans have undergone a distortion of their skulls so the nostrils are pushed back atop the head. This enables the animal to breathe at the surface without lunging out of the water. It only needs to break the seas surface with the top of its head, open the blow hole quickly and exhale, then inhale quickly, close its blow hole, and submerge. It takes only two to three seconds and may be repeated several times before a deep dive. In large whales the moisture of their warm breath condenses when it hits the air and together with a little mucus and seawater a characteristic spout or blow which sometimes can be used to identify the whale. Cetaceans have all but lost their necks as the cervical vertebra are compressed and blubber fills in the natural constriction behind the head.
Adaptation of bones that make up the flippers
Bones in cetaceans are also lighter as a result of being buoyed up by water and blubber. Beached cetaceans can suffer serious injuries because of the lack of support.
Seals: Eared seals (Otariidae) including fur seals and sea lions use front flippers for swimming and can turn their hind flippers forward to walk on land, have visible ear flaps and usually found in warmer waters. True seals (Phocidae) are propelled through the water by their hind flippers and these can't support their weight on land and get drug helplessly behind.
Walruses (Odobenidae) use both front and hind flippers for swimming. The upper canine teeth in both males and females develop into large tusks used to hoist them onto the ice and dig clams and mussels in 300'water.
Sea Otters (Mustelidae) uses stone tools when it feeds cradling them on their abdomens and smashing open shells of clams or sea urchins. They also have no blubber and with dense fur and oil secreted from numerous glands, a layer of air is trapped under the fur to prevent excessive loss of heat. Also otters eat urchins which feed on holdfasts (supporting structures of kelp) and have helped kelp forests survive. With the decreased population of otters, the kelp forests showed marked destruction.
Polar bears (Ursidae) Have white fur to help them blend into the snow/ice around them, possesses thick fur a layer of insulating hair on their paws, and a thick layer of blubber and are streamlined more than other bears to help them swim better.
Streamlining in birds allows them to pass through the air and water with least effort and best fuel economy. Gannets are quick strong flyers and can dive into the water going down 30 feet to capture their food.
Fur, except in otters which trap air bubbles under their fur, is generally used for insulation in the air . Most marine mammals have to depend on blubber for insulation. Blubber is a thick layer of fatty tissue between the skin and muscles. The amount depends on the species and the season. Species living in ice latitudes have thicker blubber than those in warmer latitudes. Its buoyant and helps keep whales and dolphins afloat. Right whales have blubber 28" thick and float when killed. Besides insulation, its a food reserve. Whales feed on fatty shrimp-like krill in colder waters and as they move to warmer waters where food is less abundant, they draw on their blubber as food reserves, thinning their layer out.
Pinnipeds have a fat layer usually thinner than cetaceans (3"). Male fur seals when they come ashore to breed, have flaps of fat hanging from them but after the season, are relatively thin. During nursing, females draw from these reserves for milk production.
Birds also have fatty tissue within them that serve as a food reserve when they are migrating. With little time to eat when heading towards their feeding grounds, they get their energy from their reserves. (duck hunters know there are fat deposits on the ducks in the early season but not late in the season)
Teeth -- Dolphins and porpoises and sperm
whales are well equipped with teeth 42-300) They use them to
hold their quarry not to chew. 
Rorquals have bony plates with hairy edges inside their mouths instead of teeth. The plates are called baleen and are made of the same substance as our hair and fingernails. They feed by straining the food out of the water, swimming with their mouths open.
Seals and sea lions also use their teeth to hold their prey rather than chew while manatees use lips to gather plants that make up their diet.
Bird bills range from the huge bill and pouch of the pelican to tiny bills of the sandpipers to the broad bill prion which has strainers on the edges of the bill like baleen.
Ears
Most Marine mammals have no external ears but fur seals and
sea lions do but they lay back while swimming. Small openings
mark the ears in birds and true seals. In cetaceans and
sirenians, a crease shows where the ear is.
Nostrils
Cetaceans have nostrils (blow hole) on the top of their
heads. Toothed cetaceans have had both nostrils merge as one
blow hole which remains sealed during its dive. The sperm
whale the nostril has its blow hole located on the left side
of the head. Pinnipeds have nostrils that close when relaxed
so they, like cetaceans must make a conscious effort to
breathe.
Water Fish eating dolphins get their water from the fish they eat, Orcas, feeding on birds and mammals, get water from them but both groups take in some seawater with their food. Seals and sea lions take no seawater in with their food but whales walrus and sea otters eat invertebrates whose body fluids are close to the salinity of sea water. One reserve is the fat because when it is burned up, water is a by-product.
Water conservation. Cetaceans have no sweat glands and lose little water to the atmosphere when breathing because of the humid air near the surface of the sea. Kidneys also dispose of excess salt.
Birds have a pair of glands near the nasal passages in the head which help secrete excess salt. These are found in all birds but not always functional and usually only work when excess salt is present (after feeding).
Temperature control:
Body temp. regulation in most marine mammals occurs through the flippers/forelimbs, and flukes or hind limbs. These flattened hands/feet are thin sheets of flesh with no blubber but are abundantly irrigated and allow cooling of the blood. Each artery that feeds these limbs is surrounded by veins that join to form a sheath through which the blood returns to the heart. The blood in the veins, cooled by having circulated in the cold limb, is warmed by the transfer of heat from the arteriole blood, which is cooled in the process. As the venous blood returns to the heart it is progressively warmed and there is little heat loss to the outside of the body, as the flipper/fin is irrigated by blood that is already cold. To the other extent, the venous blood can bypass the heat exchanger and return through another network of veins close to the skin that have no insulation.
The rest of the body is insulated by a layer of blubber and the peripheral blood circulation can slow /reduce during each dive.
Seals use their skin as a heat exchanger opening or closing tiny blood vessels in the skin capable of exchanging heat with the air. Sea otters are the least adapted but has developed a way to use the properties of its coat to trap small air bubbles which engulf the otter when it dives.
Birds with their greased feathers can control individual feathers in positions that allow precise degrees of ruffling to imprison air either before or after a dive. The feet can cool the animal off easily if needed or to retain heat, be retracted within the belly feathers.
Digestion The marine birds and mammals swallow their food whole, none is equipped for chewing.These whole shrimp, fish etc. are dissolved by gastric juices and possibly ground up by gravel and stones in the stomach or crop.
Cetaceans have a three part stomach (cattle etc.) with the 1st part a great widening of the esophagus. In whales this part has stones to grind up food. the second section of the stomach is like the human stomach, secreting HCl and pepsin. The third stomach is smoothed-walled but has a few glands that secrete digestive juices. Rorquals can hold up to a ton of krill in the 1st two stomach sections. After the stomachs, the food then passes to the small and large intestines.
Pinnipeds also have stones in their stomachs but one mystery is the huge length of their intestines which is usually short in carnivores/ its 3x longer than a cow.
Breathing: Cetaceans exhale up to 80-95% of the air in their lungs (man 15-25%) and pinnipeds about 35%, sirenians, 50%. Exceptional development of the diaphragm muscles (compared to man) in cetaceans and more floating ribs, may give them a more flexible and powerful breathing pump. It takes a rorqual two seconds to exhale and inhale 1500 gallons of air and man 4 seconds to exhale and inhale a pint.
Diving: When mammals dive, the heart beats slower (bradycardia) 15-50% slower, and blood supply to less essential areas of the body is shut off by sphincter muscles in some arteries ( goes to heart, brain, lungs, muscles not stomach and kidneys). By shutting down, less O2 is needed for the dive. Oxygen is also not stored as a gas but is either accumulated as chemical combinations as oxides in blood or muscles or dissolved in organic liquids and tissues.
Cousteau, The Ocean World, Chp 9 pp 196-210, 1979.
Special adaptations include substantial amounts of myoglobin and large volumes of blood. Myoglobin in the muscle tissues binds a large amount of oxygen. The large pool of blood allows for a storage place for Oxygen. the blood is also a storage site for glucose (more because more blood). Small twisted blood vessels forming spongy masses in fatty tissue (retia mirabilia) seem to regulate blood pressure during the dive so brain, heart and lungs are supplied with constant blood pressure. The pressure on the blood stored in the RM forces blood into the vital organs.
During deep dives, the outside pressure squeezes their ribs as the volume of air in the lungs decrease. The ribs of many diving mammals are designed to collapse inwardly. Human divers as they dive deeper, take air in under the pressure which dissolves in their blood. As they ascend, this gas must get out of the solution in the blood or air bubbles will form , embolism or the bends. cetaceans take very little air down in their lungs, rather it is in solution as above and it can't expand beyond its original volume when ascending because the original volume was taken in at the surface rather than at the bottom under pressure.
Using Oxygen, glucose is broken to CO2, water and energy but once the O2 is used up, glucose is broken down anaerobically to lactate releasing a little energy, so they can use glucose in a mixed anaerobic/aerobic metabolism..one of the most important modifications ...oxidize lactate!
Echo-location and vocalization
Because their sense of smell is so limited, any marine mammals have developed echolocation, natures version of sonar. The animal emits sound waves which travel 5x faster in water and listens for echoes reflected back from the surrounding objects. The echoes are analyzed by the brain. Most toothed whales , some pinnipeds and some baleen whales may also echolocate. (Bats Too)!
The sounds of echolocation consists of short bursts of sharp clicks repeated at different frequencies. Low frequency clicks have high penetrating power and can travel long distances. The clicks, squeaks and whistles of cetaceans are produced and air is forced through air passages and air sacs while the blow hole is closed..no vocal cords so the frequencies are changed by contracting and relaxing muscles along the air passages and sacs. A fatty substance on the forehead, the melon appears to focus and direct sound waves..this gives them the rounded forehead. In toothed whales incoming sound waves are received primarily by the lower jaw. Ear canals are reduced or blocked in most cetaceans. The jawbone is filled with fat and oil and transmits sound to the two very sensitive inner ears...each independently.
Behavior..the brain has evolved into complex behaviors like learning..not instinct dominates...they rely on past experiences.
Most live in groups at least part of the time. Vocalizations play a prominent role in communications loud barks, whimpers, sedate grunts, whistles, chirps, moos, barks...there have been over 70 calls identified of the killer whales. and there are different dialects. Cetaceans show play behavior and the great whale breaches, some stick their heads out of the water to spy.
Migration
Most migrate from cold polar waters to warmer areas in response to amount of food. In the fall, the food in the polar waters becomes scarce and most cetaceans migrate to warmer waters. The pacific gray whale migrates 11,000 miles from the Aleutian to the Baja Peninsula.
Reproduction
Migration and reproduction are closely interrelated: and adaptations are...birth of seal pup must be exactly timed to coincide with the mothers return to the breeding area 11 months later because the pup would drown if born at sea. Whales must reach war water prior to giving birth. Therefore, gestation must be timed exactly.
In certain fur seals, the period is lengthened by stopping development of the embryo for several months. The embryo does not attach to the wall of the uterus after descending from the fallopian tube. the delayed implantation of the embryo lasts 4 months. It then attaches to the wall and begins to develop. The delayed implantation enables the mother to complete nursing her pup, and gives her body a chance to build up the necessary food reserves to ensure the developing fetus will be supplied nutrients during gestation.
In streamlining the body the sex organs became internal. The penis is inside the body held by retractor muscles attached to the pelvis. Connective tissue and a penis bone or baculum keep the penis rigid. Copulation in cetaceans is belly to belly and is brief being difficult to maintain contact in the sea.
Baby whales are born tail first and guided to the surface for its first breath by its mother. Gray whales weigh 907 kg at birth and 19 ft. long. Baby blue whales gain 90 kg each day. The high fat and protein content of the milk (10x fat of cow milk) milk is pumped into the young 9.5l/2-3 sec. 50x /day makes 490 l of milk daily.
Birth rate is low one / 3 years and offspring are looked after for some time.