Cetacean Characteristics and Facts By Jennifer Kennedy Updated May 01, 2016. The word cetacean is used to describe all whales, dolphins and porpoises in the order Cetacea. This word comes from the Latin cetus meaning "a large sea animal," and the Greek word ketos, meaning "sea monster." There are about 89 species of cetaceans. The term "about" is used because as scientists learn more about these fascinating animals, new species are discovered or populations are re-classified. Cetaceans range in size from the tiniest dolphin, Hector's dolphin , which is just over 39 inches long, to the largest whale , the blue whale , which can be over 100 feet long. Cetaceans live in all of the oceans and many of the major rivers of the world. Cetaceans are thought to have evolved from even-toed ungulates (a group that includes cows, camels and deer). Types of Cetaceans There are many types of cetaceans , which are divided largely according to how they feed.

The order Cetacea is divided into two sub-orders, the Mysticetes ( baleen whales) and the Odontocetes ( toothed whales ). continue reading below our video Test Your General Science Knowledge The Odontocetes are more numerous, comprising 72 different species, compared to 14 baleen whale species . The Mysticetes include species such as the blue whale , fin whale , right whale and humpback whale . Mysticetes have hundreds of comb-like plates of baleen hanging from their upper jaw. Baleen whales feed by gulping large amounts of water containing hundreds or thousands of fish or plankton, then forcing the water out in between the baleen plates , leaving the prey inside to be swallowed whole. Odontocetes include the sperm whale , orca (killer whale), beluga and all of the dolphins and porpoises. These animals have cone-shaped or spade-shaped teeth and usually capture one animal at a time and swallow it whole. Odontocetes feed mostly on fish and squid, although some orcas prey on other marine mammals .

Cetacean Characteristics Cetaceans are mammals, which means they are endothermic (commonly called warm-blooded) and their internal body temperature is about the same as a human's. They give birth to live young and breathe air through lungs just like we do. They even have hair . Unlike fish, which swim by moving their heads from side-to-side to swing their tail, cetaceans propel themselves by moving their tail in a smooth, up-and-down motion. Some cetaceans, such as the Dall's porpoise and the orca ( killer whale ) can swim faster than 30 miles per hour. Breathing When a cetacean wants to breathe, it has to rise to the water surface and exhale and inhale out of the blowholes located on top of its head. When the cetacean comes to the surface and exhales, you can sometimes see the spout , or blow, which is the result of the warm air in the whale's lungs condensing upon reaching the cool air outside. Insulation Whales do not have a coat of fur to keep warm, so they have a thick layer of fat and connective tissue called blubber underneath their skin.

This blubber layer can be as much as 24 inches thick in some whales. Senses Whales have a poor sense of smell, and depending on where they are, they may not be able to see well underwater. However, they have excellent hearing. They do not have external ears, but have tiny ear openings behind each eye. They can also tell the direction of sound underwater. Diving Whales have collapsible rib cages and flexible skeletons, which allows them to compensate for high water pressure when they dive. They can also tolerate higher levels of carbon dioxide in their blood, allowing them to stay underwater for up to 1 to 2 hours for large whales. The Marine Mammal Center : Classification Sea Otter Taxonomy Marine mammals are mammals that have adapted to life in the ocean. Marine mammals have all the characteristics of mammals, yet they are distinctive in their appearance and survival strategies. Learning to identify marine mammals is made easier by learning their scientific classification or taxonomy. Order Carnivora includes five families of marine mammals: Three of the families within the order are called “pinnipeds” which means “flipper-footed”.

Pinnipeds regularly come out on land to rest, breed, and give birth and are comprised of the following three families: Family Otariidae: sea lions and fur seals have visible external ears and can walk on all four flippers by rotating their rear flippers forward under their body. They are more mobile on land than true seals and are often seen in zoos and aquariums. Their swimming power comes from their large front flippers. In California, this family includes the California sea lions , Steller sea lions , northern fur seals , and Guadalupe fur seals . Family Phocidae: true seals have no external ears and crawl on land because their front flippers are small and their hind flippers cannot rotate forward. Their swimming power comes from their large, fan-like rear flippers. In California, this family includes Pacific harbor seals and northern elephant seals . Family Odobenidae: walruses are distinctive for their two long tusks. Walruses inhabit the Arctic seas and ice floes. They have no external ears, but can rotate their hind flippers and walk on land.

They are set apart from other pinnipeds not only by their tusks, but also by the presence of two large air pouches, or sacs, extending from each side the pharynx (in the neck). These pouches can be inflated to hold the head above water when sleeping or used as resonance chambers to enhance underwater sound. The other marine mammals in Order Carnivora are sea otters and polar bears. They can be referred to as "fissipeds," meaning paw or pad-footed. Family Mustelidae: sea otters are the only marine member of the mustelid family, which includes land mammals such as river otters, weasels, and badgers. Sea otters are the smallest marine mammals. They do not inhabit the open ocean, but instead live among coastal kelp beds, where they dive and hunt for a variety of shellfish and marine invertebrates. With their exceptionally thick, dark fur, longer tail, lack of true flippers, and their ability to use a rock as a feeding tool, sea otters are easily distinguished from other marine mammals. Sea otters are found off the central coast of California and in Washington, British Columbia, Canada, Alaska, and Russia.

Family Ursidae: Polar bears are designated as marine mammals because they depend on the ocean for a majority of their food. Thus, they are protected under marine mammal protection laws. Polar bears range throughout the Arctic regions, including parts of Alaska and Canada. Order Cetacea includes the whales, dolphins, and porpoises: All species are completely aquatic, and they cannot survive on land. They have two front flippers, and their tails are uniquely shaped into two horizontal extensions, called flukes, which provide tremendous swimming power. There are two suborders of cetaceans : Suborder Odontoceti: toothed whales are highly variable in body shape and size and include dolphins, porpoises, narwhal, beluga, beaked, and sperm whales. Toothed whales have variable numbers of teeth, or may have no functional teeth at all, and breathe through a single blowhole. Suborder Mysticeti: baleen whales include blue, gray, humpback, and bowhead whales. Instead of teeth, baleen whales have rows of strong, closely spaced baleen plates along both sides of their upper jaws. These plates filter out and trap small fish and plankton, which the whale then swallows.

Baleen whales breathe though a pair of blowholes. Order Sirenia includes the dugongs and manatees. All species live in warm or tropical waters and feed on plants. In the U.S., manatees are found in areas of coastal Florida. Another species of sirenian, called the Steller sea cow, once inhabited Arctic waters, but was hunted to extinction by 1768 within 27 years of its discovery. Adopt Repo! Mammals - NatureWorks Mammals Scientists have organized mammals into orders based on their characteristics and their structures. Scientists are still trying to figure out how some mammals are related. All mammals share three characteristics not seen in other animals. They have three middle ear bones, they have hair and they produce milk for their young. There are about 5,000 species of mammals. Scientists have organized mammals into about 26 orders based on characteristics and structure. There are three subclasses of mammals: prototheria, metatheria and eutheria. Monotremata is the only order in the prototheria subclass. Monotremes are so different from other mammals that scientists think they may be descended from a separate mammal-like reptilian stock.

The duck-billed platypus is in this order. Marsupials make up the metatheria subclass. With 19 orders, eutheria is the largest subclass of mammals. Prototheria Monotremata - platypus, echidnas Monotremes lay eggs and they have no teeth! They are only found in Australia and New Guinea. There are two species of monotremes, the platypus and the echidnas or spiny anteaters. Dasyuromorphia - quolls, dunnarts, numbat, Tasmanian Devil. The animals in this order are found in Australia, Tasmania and New Guinea. They are carnivores and insectivores. Animals in this order include quolls, dunnarts, Numbat and the Tasmanian Devil. The order has about 63 species. Top Didelphimorphia - opossums There are about 60 species of opossums in this order. They are marsupials. Most of them live in Central and South America, but one, the Virginia opossum , lives in the United States.

Opossums have a prehensile tail and some, but not all, have a pouch. A prehensile tail can curl around things and hold onto them. Top Diprotodontia - wombats, kangaroos, wallabies, koalas There are over 100 different species of diprotodontia. They are marsupials. The second and third toes on their hind feet are joined together. Animals in this order include: wombats, kangaroos, wallabies and koalas. Microbiotheria - Monito del Monte There is only one species in this order, the Monito del Monte or little mountain monkey. The Monito del Monte is a semi-arboreal South American marsupial that scientists believe is more closely related to Australasian marsupials than it is to marsupials in the Americas. The Monito del Monte is the size of a mouse. It has a prehensile tail; brown fur; short, round ears and black rings around its eyes. Notoryctemorphia - marsupial moles This order includes the marsupial moles that live in the deserts of western Australia.

There are two species in the order - the southern marsupial mole and the northern marsupial mole. Paucituberculata - shrew opossums This order is made up of five species of shrew opossum. These small, shrew-like marsupials live in the Andes mountains in South America. Shrew opossums are about the size of a rat. They are mostly carnivorous and eat insects, earthworms and small vertebrates. Top Peramelemorphia - bandicoots The animals in this order are bandicoots. Bandicoots are marsupials. They have small, compact bodies, pointed heads and strong front claws. Their pouch opens from the back. Bandicoots are found in Australia, Tasmania and New Guinea. There are about 22 species in this order. Top Artiodactyla - pigs, hippos, giraffes, camels, moose, goats, bison, deer There are over 150 species in this order. They are herbivores and have an even number of toes. Most of the artiodactyla have four-chamber stomachs.

They are native to all of the continents except for Australia and Antarctica. Species include: pigs, hippos, giraffes, camels, sheep, goats, bison, cows, moose, deer and pronghorns. Top Carnivora - dog family, cat family, bears, raccoons, sea lions, seals Most carnivores are meat eaters. Their jaws can only move vertically, or up and down. Most carnivores have sharp side teeth, or canines, that help them sever meat. Animals in this order include: dog family, cat family, bears, raccoons, sea lions, seals, walruses, weasels, skunks, otters, badgers, civets, mongooses and hyenas. There are over 260 mammals in this order. Top Cetacea - whales, dolphins, and porpoises Cetaceans have long torpedo-shaped bodies and tails that end in flukes. They have an air or blow hole on the top of their head. Like most mammals, they give birth to live young and feed them milk. There are about 80 species in this order.

Top Chiroptera - bats There are over 900 species of bats on earth. In fact, bats make up about 20 percent of all known living mammal species. Bats are also the only mammal that can fly. They are found in all parts of the world, except for Antarctica and the Arctic. Top Dermoptera - flying lemurs or colugos This order has only one family with two species in it. Flying lemurs are about the size of a squirrel. They have skin flaps on their arms and legs that let them glide. Flying lemurs are found in southeast Asia. Top Hyracoidea - hyraxes Hyraxes are about the size of rabbits. They have short necks, round heads, and short tails. They have three toes on their hind feet and five on their fore feet. On the first and third toe of their hind feet they have hooves; the middle toe has a claw. Top Insectivora - shrews, moles, hedgehogs Most of the insectivores eat only insects. There are over 350 species of insectivores. They are usually very small animals that use hearing and smell more than sight to find prey.

They are found all over the world, except for Australia. Top Lagomorpha - rabbits, hares and pikas Lagomorphas typically have long ears, short tails, and strong back legs. Pikas are the exception. They have short ears and no tail. Lagomorphs are herbivores and have strong, sharp incisors that help them clip plant parts and chew on bark. Top Macroscelidea - elephant shrews There are 28 species of elephant shrews. They have long elephant-like snouts, long hind legs, big ears and eyes, and long tails. They are found in Africa. Their long hind legs make them very good jumpers. They used to be classified in the Insectivora order, but scientists discovered that they have a different structure. Top Perissodactyla - horses, rhinos, tapirs, zebras There are 15 species in this order. The perissodactyla have hooves and an odd number of toes on their hind feet. They are herbivores. Top Pholidota - pangolins (spiny anteaters) There are seven species of pangolins in the world. They eat ants and live in Asia and Africa.

They have very long tongues and their bodies, except for their faces and bellies, are covered in large scales. Pangolins have no teeth. Top Primates - lemurs, monkeys, marmosets, apes, humans Most primates have opposable thumbs, flat nails on their toes and fingers instead of claws, large brains, and foward-facing eyes in the front of their face. Top Proboscidea - elephants Elephants are very large. They have large ears and trunks. Males have tusks. They are herbivores and can live for 60 or more years. Top Rodentia - squirrels, chipmunks, rats, mice, voles, beavers, lemmings These are the rodents! They are small animals that gnaw. They have long, sharp incisors on both the lower and upper jaw. Most rodents are herbivores. There are over 2000 species of rodents. They make up almost half of all the mammal species. They are found in all parts of the world except for Antarctica and New Zealand. Top Scandentia - tree shrews There are 19 species of tree shrews.

Tree shrews have long tails, a pointed nose, and sharp curved claws. Like the elephant shrew they were once considered insectivores, but they are structurally different and were given their own order. They also have some of the feature of primates and were sometimes placed in that order. Top Sirenia - dugongs and manatees These mammals are adapted to spend all of their time in water. They have flippers for front limbs and a flat tail. They have thick bristles on their lips. They are herbivores and eat aquatic vegetation. Top Tubulidentata - aardvark Aardvarks are pig-sized animals with long snouts. They eat insects. They have long, flat, front claws that they use to dig into termite mounds. They have very thick skin, large rabbit-like ears, short legs and little hair. Top Xenarthra - sloths, armadillos, true anteaters There are 31 species of Xenarthra in the world. They are found in Central and South America and the United States. They have long, sticky tongues, long claws on their front feet, a small brain, and five toes on their hind feet.

Cetacea C Cetacea The order Cetacea (pronounced /sɨˈteɪʃ(i)ə/, L. cetus, whale, from Greek) includes whales , dolphins , and porpoises . Cetus is Latin and is used in biological names to mean "whale"; its original meaning, "large sea animal", was more general. It comes from Ancient Greek κῆτος (kētos), meaning "whale" or "any huge fish or sea monster". In Greek mythology the monster Perseus defeated was called Ceto, which is depicted by the constellation of Cetus . Cetology is the branch of marine science associated with the study of cetaceans. Cetaceans are the mammals best adapted to aquatic life. Their body is fusiform (spindle-shaped). The forelimbs are modified into flippers. The tiny hindlimbs are vestigial; they do not attach to the backbone and are hidden within the body. The tail has horizontal flukes. Cetaceans are nearly hairless, and are insulated by a thick layer of blubber . As a group, they are noted for their high intelligence.

The order Cetacea contains about ninety species, all marine except for four species of freshwater dolphins . The order is divided into two suborders, Mysticeti (baleen whales) and Odontoceti (toothed whales, which includes dolphins and porpoises). The species range in size from Commerson's Dolphin, smaller than a human, to the Blue Whale , the largest animal known to have lived. Respiration As mammals, cetaceans need to breathe air. Because of this, they need to come to the water's surface to exhale carbon dioxide and inhale a fresh supply of oxygen . During diving, a muscular action closes the blowholes (nostrils), which remain closed until the cetacean next breaks the surface; when it surfaces, the muscles open the blowholes and warm air is exhaled. Cetaceans' blowholes have evolved to a position on top of the head, allowing more time to expel stale air and inhale fresh air. When the stale air, warmed from the lungs, is exhaled, it condenses as it meets the cold air outside. As with a terrestrial mammal breathing out on a cold day, a small cloud of 'steam' appears.

This is called the 'blow' or 'spout' and is different in terms of shape, angle and height, for each cetacean species. Cetaceans can be identified at a distance, using this characteristic, by experienced whalers or whale-watchers. Cetaceans can go underwater for much longer periods of time than other mammals. Their duration under water varies greatly between species due to large physiological differences between many members of this Order. There are two studied advantages of cetacean physiology that let this Order (and other marine mammals) forage underwater for extended periods of time without breathing at the water surface. Myoglobin concentrations in skeletal muscle of mammals have much variation. A New Zealand white rabbit has 0.08+/-0.06 g (in a 100 g Wet muscle) of myoglobin , whereas a Northern Bottlenose Whale has 6.34 g (in a 100 g Wet muscle) of myoglobin. Myoglobin, by nature, has a higher affinity to oxygen than hemoglobin . That is, myoglobin retains oxygen molecules better than hemoglobin.

Therefore, it is useful to have higher concentrations of myoglobin when needed and there is no oxygen available for re-uptake. The higher the myoglobin concentration in cetacean skeletal muscle, the longer they can stay underwater and forage. Increased body size is another way of elongating dive duration of large cetaceans. This is true because of two considered aspects. An increase in body size means that there is increase in muscle mass, therefore, increase in muscle oxygen stores. Another aspect is the universal correlation of mass and metabolic rate (Kleiber's law). In layman’s terms, Kleiber’s law states that the metabolic rate of a large animal is slower than a small animal per unit mass. From this we can conclude that larger animals will use up less oxygen than smaller animals (per mass unit). Vision, hearing and echolocation Cetacean eyes are set well back and to either side of its head. This means that cetaceans with pointed 'beaks' (such as dolphins) have good binocular vision forward and downward but others, with blunt heads (such as the Sperm Whale), can see either side but not directly ahead or directly behind.

Tear glands secrete greasy tears, which protect the eyes from the salt in the water. Cetaceans also have an almost spherical lens in their eyes, which is most efficient at focusing what little light there is in the deep waters. Cetaceans make up for their generally quite poor vision (with the exception of the dolphin) with excellent hearing. As with the eyes, cetacean ears are also small. Life in the sea accounts for the cetacean's loss of its external ears, whose function is to collect airborne sound waves and focus them in order for them to become strong enough to hear well. However, water is a better conductor of sound than air, so the external ear was no longer needed: it is no more than a tiny hole in the skin, just behind the eye. The inner ear, however, has become so well developed that the cetacean can not only hear sounds dozens of miles away, but it can also discern from which direction the sound comes. Some cetaceans are capable of echolocation. Many toothed whales emit clicks similar to those in echolocation, but it has not been demonstrated that they echolocate.

Mysticeti have little need of echolocation, as they prey upon small fish that would be impractical to locate with echolocation. Some members of Odontoceti, such as dolphins and porpoises, do perform echolocation. These cetaceans use sound in the same way as bats—they emit a sound (called a click), which then bounces off an object and returns to them. From this, cetaceans can discern the size, shape, surface characteristics and movement of the object, as well as how far away it is. With this ability cetaceans can search for, chase and catch fast-swimming prey in total darkness. Echolocation is so advanced in most Odontoceti that they can distinguish between prey and non-prey (such as humans or boats); captive cetaceans can be trained to distinguish between, for example, balls of different sizes or shapes. Cetaceans also use sound to communicate , whether it be groans, moans, whistles, clicks or the complex 'singing' of the Humpback Whale . Feeding When it comes to food and feeding, cetaceans can be separated into two distinct groups.

The toothed whales, Odontoceti like the Sperm Whale, Beluga, dolphins and porpoises, usually have lots of teeth that they use for catching fish, squid or other marine life. They do not chew their food, but swallow it whole. In the rare cases that they catch large prey, as when the Orca (Orcinus orca) catches a seal, they tear chunks off it that in turn are swallowed whole. The baleen whales or Mysticeti do not have teeth. Instead they have plates made of keratin (the same substance as human fingernails) which hang down from the upper jaw. These plates act like a giant filter, straining small animals (such as krill and fish) from the seawater. Cetaceans included in this group include the Blue Whale, the Humpback Whale, the Bowhead Whale and the two minke whale species. Not all Mysticeti feed on plankton: the larger whales tend to eat small shoaling fish, such as herrings and sardines, called micronecton. One species of Mysticeti, the Gray Whale (Eschrichtius robustus), is a benthic feeder, primarily eating sea floor crustaceans .

Mammalian nature Cetaceans are mammals, that is, members of the class Mammalia. The closest living relative of cetaceans is the hippopotamus. As mammals, cetaceans have characteristics that are common to all mammals: they are warm-blooded , breathe in air through their lungs, bear their young alive and suckle them on their own milk , and have hair , although very little of it. Another way of discerning a cetacean from a fish is by the shape of the tail. The tail of a fish is vertical and moves from side to side when the fish swims. The tail of a cetacean—called a fluke—is horizontal and moves up and down, as cetaceans' spines bend in the same manner as a human spine. Taxonomic listing The classification here closely follows Dale W. Rice, Marine Mammals of the World: Systematics and Distribution (1998), which has become the standard taxonomy reference in the field. There is very close agreement between this classification and that of Mammal Species of the World: 3rd Edition (Wilson and Reeder eds., 2005).

Any differences are noted using the abbreviations "Rice" and "MSW3" respectively. Further differences due to recent discoveries are also noted. Discussion of synonyms and subspecies are relegated to the relevant genus and species articles. ORDER CETACEA Suborder Mysticeti: Baleen whales Family Balaenidae : Right whales and Bowhead Whale Genus Balaena Amazon River Dolphin, Inia geoffrensis Bolivian River Dolphin, Inia boliviensis † Family Lipotidae - MSW3 treats Lipotes as a member of Iniidae † Genus Lipotes Family Pontoporiidae - MSW3 treats Pontoporia as a member of Iniidae Genus Pontoporia Family Platanistidae Genus Platanista Ganges and Indus River Dolphin, Platanista gangetica. MSW3 treats Platanista minor as a separate species, with common names Ganges River Dolphin and Indus River Dolphin, respectively.

Family Ziphidae, Beaked whales Arnoux's Beaked Whale, Berardius arnuxii Baird's Beaked Whale (North Pacific Bottlenose Whale), Berardius bairdii Subfamily Hyperoodontidae Northern Bottlenose Whale, Hyperoodon ampullatus Southern Bottlenose Whale, Hyperoodon planifrons Genus Indopacetus Indo-Pacific Beaked Whale (Longman's Beaked Whale), Indopacetus pacificus Genus Mesoplodon, Mesoplodont Whale Sowerby's Beaked Whale, Mesoplodon bidens Andrews' Beaked Whale, Mesoplodon bowdoini Hubbs' Beaked Whale, Mesoplodon carlhubbsi Blainville's Beaked Whale, Mesoplodon densirostris Gervais' Beaked Whale, Mesoplodon europaeus Ginkgo-toothed Beaked Whale, Mesoplodon ginkgodens Gray's Beaked Whale, Mesoplodon grayi Hector's Beaked Whale, Mesoplodon hectori Layard's Beaked Whale, Mesoplodon layardii True's Beaked Whale, Mesoplodon mirus Perrin's Beaked Whale, Mesoplodon p

errini.

This species was recognised in 2002 and as such is listed by MSW3 but not Rice. Pygmy Beaked Whale, Mesoplodon peruvianus Stejneger's Beaked Whale, Mesoplodon stejnegeri Spade Toothed Whale, Mesoplodon traversii Genus Tasmacetus Tasman Beaked Whale (Shepherd's Beaked Whale), Tasmacetus shepherdi Genus Ziphius Cuvier's Beaked Whale, Ziphius cavirostris †Extinct (Wikipedia) Cetacea Cetacea Click on an image to view larger version & data in a new window This tree diagram shows the relationships between several groups of organisms. The root of the current tree connects the organisms featured in this tree to their containing group and the rest of the Tree of Life. The basal branching point in the tree represents the ancestor of the other groups in the tree. This ancestor diversified over time into several descendent subgroups, which are represented as internal nodes and terminal taxa to the right.

You can click on the root to travel down the Tree of Life all the way to the root of all Life, and you can click on the names of descendent subgroups to travel up the Tree of Life all the way to individual species. For more information on ToL tree formatting, please see Interpreting the Tree or Classification . To learn more about phylogenetic trees, please visit our Phylogenetic Biology pages. close box Containing group: Eutheria Introduction Cetaceans (whales, dolphins and porpoises) form one of the most dramatically-derived group of mammals. Indeed, during their transition from the terrestrial to the aquatic environment, they experienced spectacular transformation of many biological systems and acquired a fusiform body shape giving modern families a superficial resemblance to fish. Extant cetaceans comprise approximately 87 species in 14 families and two sub-orders: Mysticeti (baleen-bearing whales) and Odontoceti (teeth-bearing whales) (Rice, 1998). Adult size ranges from less than 1.5 meters for some representatives of the Cephalorhynchus genus, to more than 30 meters for the largest blue whales.

Cetaceans are ecologically very diverse as their habitats vary from coastal to pelagic, from tropical to polar, and from marine to fresh water, while their preys vary from planctonic crustaceans to fish, squids, and marine mammals. Characteristics The major morphological transformations related to the transition to the aquatic environment include: Loss of external hind limbs, although vestigial pelvic girdle bones are still present in all extant species; Paddle-like forelimbs with hyperphalangy and a non-rotational elbow joint; Torpedo-shaped body, with addition of vertebrae, reduction of the neck, and development of a horizontal caudal tail; Development of a thick blubber layer that prevents heat-loss; Telescoping of the skull, and posterior movement of the narial openings. The position of the external nares on the top of the skull allows cetacean to breathe while keeping the rest of the head underwater. The telescoping of the skull mostly involves the posterior extension of the bones of the elongated rostrum: maxillae, premaxillae, vomer and mesethmoid; Isolation of the earbones related to the development of underwater hearing and echolocation abilities.

Breathing In mysticetes the nasal passages are separate tubes all the way to the external nares, whereas in odontocetes, the two nasal passages branch into a complex series of nasal sacs that eventually coalesce into a single blowhole. The sperm whale is however intermediate as it exhibits a sigmoidally-shaped blowhole formed by two nasal tubes that remain distinct from the bony nares to the top of the head: the anterior and posterior curves of the sigmoid blowhole represent the apertures of the right and left nares, respectively (rare examples of adult sperm whales with two distinct blowholes have even been reported). In the pygmy sperm whales (Kogiidae), the situation is only slightly different since the nasal passages remain discrete tubes until just proximal to the single blowhole. Click on an image to view larger version & data in a new window Left: Toothed whales have a single blowhole. Right: Baleen whales have two blowholes. © Michel C. Milinkovitch Click on an image to view larger version & data in a new window In the giant sperm whale, the nasal passages remain discrete tubes until just proximal to the single s-shaped blowhole. © 1989 John E.

Heyning. Hearing and Echolocation Echolocation is the ability to assess the environment (mostly, detecting obstacles, conspecifics, predators, and prey) by emitting sounds and listening to the echoes. Echolocation abilities have been conclusively demonstrated in delphinoids and so-called “river dolphins” (see below) and seem to be present in beaked and sperm whales as well. Although they can easily detect an object about the size of a ping-pong ball more than 50 meters away, dolphins also use echolocation to inspect objects at very short ranges (e.g., to assess shape, size, and structure). Dolphins produce short “clicks” whose frequencies (10 to 150 kHz) and intervals (as short as 1.2 milliseconds) are adjusted depending on the size and distance of the target (high frequencies dissipate more rapidly than low frequencies but allow the detection of smaller targets and a finer analysis of shape and structure). These sounds are produced by circulation of air in a complex system of facial sacs, reflected by the cranium, and focused into a beam by the melon, a fatty structure located in the forehead and serving as an acoustic lens.

Mysticetes possess a small (Heyning 1989), possibly vestigial (Milinkovitch, 1995) melon. Click on an image to view larger version & data in a new window The melon is a a fatty structure located in the forehead of all cetaceans. In most toothed whales, it serves as an acoustic lens for echolocation sound production. The melon is shown in blue for the genera Globicephala, Inia, Ziphius, Balaena, and Physeter (from left to right). S, spermaceti organ. © 1995 Michel C. Milinkovitch The high-frequency echoes are received through the hollow mandible then transferred across fatty channels to the middle ear. Low-frequency sounds on the other hand are perceived through the auditory channels. The middle and inner ears of odontocetes are surrounded by an emulsion of mucus, oil, and air. The whole structure is enclosed into a dense, bony bulla. This high level of acoustic isolation greatly improves directional detection.

The isolation mechanism is less complete in mysticetes, but the large distance between the two ears (simply because of the size of these animals) probably helps directional detection. Mysticetes exhibit a peculiar tympanic membrane (the finger glove) and seem to receive sounds through the auditory channels. It is unclear whether mysticetes are able to rely on the echoes of their low-frequency sounds. Dorsal and anterior to the skull, sperm whales also have a large oily organ (called the “spermaceti organ” because early whalers thought the whitish oily substance was the whale semen) that possibly works as a biological ballast (Raven & Gregory 1933; Clarke 1970) or constitutes a secondary sexual character involved in acoustic display (Cranford 1999). Because of the high specialization of the giant sperm whale facial anatomy, it is unclear what structure in this species is homologous to the melon of other cetaceans.

However, based on the comparison between the facial anatomy of dwarf and pygmy sperm whales, Heyning (1989) suggested the junk (a segmented tissue located below the spermaceti case and so-called because it is less rich in oil than the spermaceti itself) rather than the spermaceti organ as the most likely candidate. This hypothesis is supported by comparative CT-scan analyses (Cranford et al. 1996). Origin of Cetacea The oldest known cetaceans are Eocene in age, appearing around 55 million years ago. These primitive toothed cetaceans, lacking odontocetes and mysticetes cranial specializations, form the paraphyletic sub-order Archaeoceti. Representatives of this group have been found in Egypt, Nigeria, India, Pakistan, and USA and show a wide range of morphologies that prompted their classification into several families such as the Pakicetidae (early Eocene), Protocetidae (middle Eocene) and Basilosauridae (middle to Late Eocene). The most primitive taxa exhibited locomotory hind limbs (see Thewissen et al. 1994; Gingerich et al.

2001; Thewissen et al. 2001). The archaeoceti fossils illustrate the progressive reduction of hind limbs, adaptations of the ear for underwater hearing, and the expansion of the pterygoid sinus fossae in the basicranium leading to a better isolation of the ear bones. Click on an image to view larger version & data in a new window Skeleton of Rhodocetus kasrani. Forelimbs were probably folded against the body during rapid swimming by pelvic paddling at the sea surface and during rapid swimming by pelvic paddling and caudal undulation when submerged. On land, Rodhocetus supported itself on hoofed digits II, III, and IV of the hands and on the plantar surfaces of the feet, and probably progressed somewhat like a modern eared seal or sea lion. Drawing from Gingerich et al. 2001. © 2001 American Association for the Advancement of Science The origin of aquatic cetaceans has to be found among terrestrial mammals living in the early Tertiary. Analyses of neontological data have long suggested that cetaceans are closely related to ungulates (e.g., Flower, 1883; Prothero et al.

1988). These results were corroborated by paleontological data (Gingerich et al. 1990; Thewissen and Hussain, 1993; Thewissen, 1994). The close relationship between cetaceans and ungulates (and especially artiodactyls) was strongly supported by basically all molecular data published to date: from immunological (e.g., Boyden and Gemeroy, 1950; Shoshani, 1986) and DNA-DNA hybridization (Milinkovitch, 1992) studies, to analyses of mitochondrial and nuclear amino-acid and DNA sequences (e.g., Czelusniak et al. 1990; Milinkovitch et al. 1993; Gatesy, 1997; Milinkovitch et al. 1998, Gatesy et al. 1999). The two main alternative hypotheses regarding the exact phylogenetic position of cetaceans within mammals are suggested respectively by morphological and molecular data.

Morphological studies suggested that artiodactyls is the sister group to Cete -- i.e., a clade comprising cetaceans and a fossil group of carnivorous hoofed mammals: the mesonychians (see e.g. O'Leary and Geisler, 1999). On the other hand, molecular studies indicate that cetaceans are highly derived artiodactyls and that hippopotamids are their extant sister group. Although the nesting of cetaceans within artiodactyls (making the latter paraphyletic) was suggested by multiple studies (Goodman et al. 1985; Czelusniak et al. 1990; Irwin et al. 1991; Graur and Higgins, 1994; Gatesy et al. 1996; Smith et al. 1996; Gatesy, 1997; Montgelard et al. 1997) the statistical support or methods of analyses have been strongly criticized (e.g., Philippe and Douzery, 1994; Hasegawa and Adachi, 1996).

This lead to a second series of molecular analyses with greatly increased taxon and gene sampling (Milinkovitch et al. 1998, Gatesy et al. 1999). These latter analyses confirmed the monophyly of Cetartiodactyla (cetaceans,artiodactyls) and clarified its phylogeny. Furthermore, phylogenetic interpretation of retropositional events that lead to the insertion of short interspersed elements (SINEs) at particular loci in the nuclear genome of various artiodactyl and cetacean ancestors (Shimamura et al. 1997; Nikaido et al. 1999) lead to the same phylogenetic tree, suggesting that the paraphyly of artiodactyls is not the result of analytical problems related to the analysis of aligned nucleotide sequences (Milinkovitch and Thewissen, 1997; Shedlock et al. 2000).

It is indeed the nature of SINE data that makes them so efficient in phylogeny inference: the likelihood of SINEs being independently inserted at the same locus in different lineages, or precisely excised in different lineages, seems virtually nil. It remains to be understood why these results are in striking contradiction to the common interpretation of the available morphological data, namely, supporting artiodactyl monophyly (e.g., O'Leary and Geisler, 1999). Note however, that the discrepancies between the morphological and molecular hypotheses have recently diminished. Indeed, recent discoveries of primitive whales from the families Pakicetidae and Protocetidae, from the early Eocene of Pakistan, allowed the description of skulls associated with hindlimbs (Thewissen et al. 2001; Gingerich et al. 2001). These fossils exhibit skull characters typical of primitive cetaceans and terrestrial hindlimbs with derived characters of artiodactyls.

The morphology of the ankle (mainly the astragalus and calcaneum) of these terrestrial cetaceans suggest that Cetacea are the sister group of monophyletic Artiodactyla, and that [artiodactyls , cetaceans] form the sister group of mesonychians. In these new trees, cetaceans are therefore getting closer to artiodactyls but these analyses of morphological characters continue to support the monophyly of the latter group and, hence, to disagree with the molecular analyses. Click on an image to view larger version & data in a new window Relationships between Artiodactyla, Cetacea, and Mesonychia based on morphological data. From Thewissen et al. (2001). Finally, Geisler and Uhen (2003) have performed maximum parsimony analyses of a matrix including substantially more taxa and morphological characters than previous analyses and found support for the sister-relationship between hippos and cetaceans, making molecular and morphological evidence for the phylogeny of these taxa much more congruent than previously thought. Discussion of Phylogenetic Relationships Some molecular studies based on mitochondrial DNA sequences (Milinkovitch et al.

1993; Milinkovitch et al. 1994) suggested that Physeteroidea (sperm whales) are more closely related to mysticetes than they are to other odontocetes. However, other molecular data (e.g., Nikaido et al. 2001; Gatesy et al. 1999) support the monophyly of toothed whales (Odontoceti). Recent analyses (Cassens et al. 2000) indicate that there is conflicting signal between the nuclear DNA and mitochondrial DNA data. Whether this conflict is due to differential lineage sorting or to misleading signal from one or several data set(s) remains to be investigated. This issue is further discussed in the Odontoceti (toothed whale) page.

Phylogenetic relationships among the families of extant cetaceans are still problematic and hypotheses on various nodes of the tree come from a variety of data: the morphology of extant taxa (including the soft anatomy) (e.g., Heyning, 1989), paleontological (e.g., Muizon 1991; Fordyce 1994; Geisler and Sanders 2003), and molecular evidence (e.g., Milinkovitch et al. 1993, 1994; Arnason and Gulberg, 1996; Cassens et al. 2000) or a combination of these (Milinkovitch 1995; Messenger and Mc Guire, 1998; Gatesy et al. 1999). This evidence will be discussed on relevant pages of cetacean subgroups. Other Names for Cetacea Whales, dolphins, and porpoises References Arnason, U. and A. Gullberg. 1996. Cytochrome b nucleotide sequences and the identification of five primary lineages of extant cetaceans.

Molecular Biology and Evolution 13:407-417. Boyden, A. and Gemeroy, D. 1950. The relative position of the Cetacea among the orders of Mammalia as indicated by precipitin tests. Zoologica, 35:145-151. Cassens, I., S. Vicario, V. G. Waddell, H. Balchowsky, D. Van Belle, Wang Ding, Chen Fan, R.S. Lal Mohan, P. C. Simï¿½es-Lopes, R. Bastida, A. Meyer, M. J. Stanhope and Michel C. Milinkovitch. 2000. Independent adaptation to riverine habitats allowed survival of ancient cetacean lineages. Proc. Natl. Acad. Sci. USA, 97:11343-11347. Clarke M.R. 1970. Function of the spermaceti organ of the sperm whale. Nature 228:873-874. Cranford T. W. 1999.

The sperm whale's nose: sexual selection on a grand scale? Marine Mammal Science 15:1133-1157. Cranford T. W., Amundin M., and K.S. Norris. 1996. Functional morphology and homology in the odontocete nasal complex: implications for sound generation. J. Morph. 228:223-285. Czelusniak, J., M. Goodman, B. F. Koop, D. A. Tagle, J. Shoshani, G. Braunitzer, T. K. Kleinschmidt, W. W. De Jong, and G. Matsuda. 1990. Pp. 545-572 In H. H. Genoways, Ed. Current Mammalology. Vol. 2. Plenum, New York. Flower W.H. 1883. On whales, present and past and their probable origin. Proc. Zool. Soc., London, 1883:466-513. Fordyce R.E. 1994.

Waipatia maerewhenua, new genus and new species (Waipatiidae, new family), an archaic late Oligocene dolphin (Cetacea: Odontoceti: Platanistoidea) from New Zealand. Proc. Sand Diego Soc. Nat Hist. 29:147-176. Gatesy, J. 1997. More DNA Support for a Cetacea/Hippopotamidae Clade: The Blood-Clotting Protein Gene y-Fibrinogen. Mol. Biol. Evol. 14(5):537-543. Gatesy, J. 1998. Molecular evidence for the phylogenetic affinities of Cetacea. pp. 63-112 in: Thewissen J.G.M. (ed.), The Emergence of Whales: Evolutionary Patterns in the Origin of Cetacea , Plenum, New York. Gatesy, J. , C. Hayashi , M. Cronin, and P. Arctander. 1996.

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Phylogenetic position of cetaceans relative to artiodactyls: Reanalysis of mitochondrial and nuclear sequences. Mol. Biol. Evol. 13:710-717. Heyning, J. E. 1989. Comparative facial anatomy of beaked whales (Ziphidae) and a systematic revision among the families of extant Odontoceti. Cont. Sci. Nat. Hist. Mus. Los Angeles 405:1-64. Irwin, D. M., T. D. Kocher, and A. C. Wilson. 1991. Evolution of the cytochrome b gene of mammals. J. Mol. Evol. 32:128-144. May-Collado, L. and I. Agnarsson. 2006. Cytochrome b and Bayesian inference of whale phylogeny. Mol. Phylogenet. Evol. 38:344ï¿½354 Messenger, S. L. and J. A. McGuire. 1998.

Morphology, molecules, and the phylogenetics of cetaceans. Systematic Biology 47:90-124. Milinkovitch, M. C. 1992. DNA-DNA Hybridizations Support Ungulate Ancestry of Cetacea. J Evol Biol, 5:149-160. Milinkovitch, M. C. 1995. Molecular phylogeny of cetaceans prompts revision of morphological transformations. Trends in Ecology and Evolution 10:328-334. Milinkovitch, M. C., M. Bï¿½rubï¿½, and P. J. Palsbï¿½ll. 1998. Cetaceans Are Highly Specialized Artiodactyls. pp. 113-131 in: Thewissen J.G.M. (ed.), The Emergence of Whales: Evolutionary Patterns in the Origin of Cetacea. Plenum, New York. Milinkovitch, M. C., A. Meyer, and J. R. Powell. 1994.

Phylogeny of all major groups of cetaceans based on DNA sequences from three mitochondrial genes. Molecular Biology and Evolution 11:939-948. Milinkovitch, M. C., G. Ortï¿½, and A. Meyer. 1993. Revised phylogeny of whales suggested by mitochondrial ribosomal DNA sequences. Nature 361:346-348. Milinkovitch, M. C., and Thewissen, J.G.M. 1997. Eventoed Fingerprints on Whale Ancestry. Nature 388:622-624. Montgelard, C., F.M. Catzeflis and E. Douzery. 1997. Phylogenetic Relationships of Artiodactyls and Cetaceans as Deduced from the Comparison of Cytochrome b and 12s rRNA Mitochondrial Sequences. Mol. Biol. Evol. 14(5):550-559. Muizon, C. de. 1990.

A new Ziphiidae (Cetacea) from the Early Miocene of Washington State (USA) and phylogenetic analysis of the major groups of odontocetes. Bulletin du Musï¿½um National d'Histoire Naturelle, Paris 4 C, (3-4): 279-326. Nikaido M., A.P. Rooney,and N. Okada. 1999. Phylogenetic relationships among cetartiodactyls based on insertions of short and long interpersed elements: Hippopotamuses are the closest extant relatives of whales. Proc. Natl. Acad. Sci. USA 96, pp. 10261ï¿½10266. Nikaido, M., Matsuno, F., Hamilton, H., Brownel, R. L. Jr, Cao, Y., Ding, W., Zuoyan, Z., Shedlock, A. M., Fordyce, R. E., Hasegawa, M., and Okada, N. 2001.

Retroposon analysis of major cetacean lineages: the monophyly of toothed whales and the paraphyly of river dolphins. Proceedings of the National Academy of Sciences 98 (13): 7384-7389. O'Leary, M.A. and J.H. Geisler. 1999. The position of Cetacea within Mammalia: phylogenetic analysis of morphological data from extinct and extant taxa. Syst. Biol. 48: 455-490. Philippe H. and Douzery E. 1994. The pitfalls of molecular phylogeny based on four species as illustrated by the Cetacea/Artiodactyla relationships. J. Mammal. Evol. 2: 133-152. Price, S. A., O. R. P. Bininda-Emonds, and J. L. Gittleman. 2005. A complete phylogeny of the whales, dolphins and even-toed hoofed mammals (Cetartiodactyla). Biol. Rev. 80:445ï¿½473.

Prothero D., Manning E. and Fisher M. 1988. The phylogeny of the unglates. IN: The phylogeny and classification of the tetrapods, volume 2: Mammals (Ed. by M. Benton), pp. 201-234. CXlarendon Press, Oxford. Raven H. C. and W.K. Gregory. 1933. The spermaceti organ and nasal passages of the sperm whale (Physeter catodon) and other odontocetes. American Museum Novitates 677: 1-18. Rice, D. W. 1998. Marine mammals of the world. Systematics and distribution. Society for Marine Mammalogy, Special Publication, 4, Lawrence, Kansas, 231 pp. Rothausen, K. 1968. Die systematische Stellungsder europaischen Squalodontidae (Odontoceti, Mammalia). Palaeontologische Zeischrift 42: 83-104. Shedlock A. M., M.C.

Milinkovitch, and N. Okada. 2000. SINE Evolution, Missing Data, and the Origin of Whales. Syst. Biol. 49(4):808ï¿½817. Shimamura M., H. Yasue, K. Ohshima, H. Abe, H. Kato, T. Kishiro, M. Goto,I. Munechikak and N. Okada. 1997. Molecular evidence from retroposons that whales form a clade within even-toed ungulates. Nature 388: 666-670. Shoshani J. 1986. Mammalian Phylogeny: Comparison of Morphological and Molecular Results. Mol. Biol. Evol. 3(3):222-242. Smith, M., M. Shivji, V. Waddell, and M. Stanhope. 1996. Phylogenetic evidence from the IRBP gene for the paraphyly of toothed whales, with mixed support for Cetacea as a suborder of Artiodactyla. Mol.

Biol. Evol. 13:918-922. Thewissen, J. G. M. 1994. Phylogenetic aspects of cetacean origins: a morphological perspective. J. Mamm. Evol. 2: 157-183. Thewissen, J. G. M. and S. T. Hussain. 1993. Origin of underwater hearing in whales. Nature 361:444-445. Thewissen, J. G. M., S. T. Hussain, and M. Arif. 1994. Fossil evidence for the origin of aquatic locomotion in archaeocete whales. Science 263:210-212. Thewissen, J. G. M. , E. M. Williams, L. J. Roe and S. T. Hussain. 2001. Skeletons of terrestrial cetaceans and the relationship of whales to artiodactyls. Nature 413: 277-281.

Wada, S., Oishi, M., and Yamada, T. K. 2003. A newly discovered species of living baleen whale. Nature 426: 278-281. Zimmer, C. 1998. At the Water's Edge: Fish with Fingers, Whales with Legs, and How Life Came Ashore but Then Went Back to Sea. Touchstone, New York. Information on the Internet Cetaceans Dolphin. Photo by Susan Middleton, © 2003 California Academy of Sciences. The Cetacea are one of the most distinctive and highly specialized orders of mammals . They include the largest animal that has ever lived, the blue whale; the highly intelligent and communicative dolphins; the tusked narwhals and blind river dolphins and singing humpback whales  nearly eighty living species in all. Although hunting and other human activities have endangered most cetacean species, the outlook for many is improving. Whales are highly specialized for life in the water. Most species are marine, but dolphin species are found in the Yangtze, Amazon, Paraná, Indus and Ganges Rivers.

Whales have streamlike bodies with highly compressed neck vertebrae, dorsal fins, and a tail with two finlike flukes arranged horizontally. Modern whales have greatly elongated anterior skull bones, and the nostrils are located on the top of the head, forming the blowhole. The forelimbs are specialized to form flippers, and the hind limbs and pelvis are extremely small and do not normally extend out of the body wall of the animal. Modern whales may be divided into two subgroups: the Odontoceti (toothed whales) and the Mysticeti (baleen whales). Odontocetes bear teeth  typically numerous and peglike, although sometimes modified, as in the single tusk of the narwhal or the odd, fanglike lower teeth of the beaked whales. Many odontocetes can navigate by echolocation, producing sound waves using a complex system of nasal sacs and passages, and using the echoes to navigate. Dolphins and porpoises are examples of odontocetes, as are belugas, narwhals, killer whales, sperm whales, and beaked whales. Baleen whales lack teeth completely as adults (although teeth are present in fetal baleen whales).

They feed by straining small marine organisms out of the water using plates of baleen, a hornlike substance that forms filaments that hang down from the roof of the mouth. Blue, right, humpback, minke, gray, and fin whales are well-known examples of baleen whales. Some baleen whales, most famously the humpack whales, are known for the strange and complex songs they produce; their function is not clear, but unlike toothed whales, baleen whales do not use their songs for echolocation. The fossil record of whales is rich, and recent discoveries have shed much light on the origin of the Cetacea. Archaeocetes: The Oldest Whales The oldest fossil whales are often grouped together, largely for convenience, in a taxon known as the archaeocetes. Archaeocetes show several features that modern whales lack. Their teeth, like those of most land mammals, still show differentiation into several types. (Modern whales either lack teeth, or have teeth that are all virtually identical in shape and size). Archaeocetes also had nostrils near the tip of the nose, like land mammals, rather than a blowhole on the top of the head.

Some retained substantial hind limbs that would have been visible outside the animal's body; in the earliest archaeocetes, these limbs and the pelvis were attached to the vertebrae by a sacral joint, but in later ones the limbs and pelvis were not attached to the rest of the skeleton. Pakicetus (right) is a Middle Eocene archaeocete from the Kuldana Formation of Pakistan; it is currently the earliest known well-preserved cetacean, and the archaeocete features are clearly visible in this replica skull from UCMP's collections. Pakicetus is so far known only from its skull, but recent finds in Pakistan have produced other whale species that show very primitive characters in both the skull and the rest of the skeleton. These animals had relatively well developed limbs, but were aquatic. Rodhocetus, a recently discovered archaeocete from Pakistan, was a few million years younger than Packicetus. Rodhocetus had well-developed hind limbs (although only the thighbone, or femur, has been preserved), but unlike land mammals, Rodhocetus did not have its vertebrae in the pelvic region fused together into a sacrum.

Early whales such as Rodhocetus show many similarities with an early group of land mammals known as mesonychids, which are also close to the root of the hoofed mammals. In fact, some fossil teeth that were once identified as mesonychids are now known to have come from archaeocetes. By the late Eocene, archaeocete whales had spread to many parts of the world. Zygorhiza is fairly common in the Gulf Coastal region of the southeastern United States. Although the body is very whale-like (though somewhat less compact than a modern whale), Zygorhiza shows differentiated teeth and nostrils near the end of the nose. Basilosaurus. Photo © Mark Uhen, Cranbrook Institute of Science. Basilosaurus (right) is another Eocene archaeocete from the Gulf Coast, with a rather unfortunate name: Dr. Richard Harlan, the 19th-century American physician who described and named it, believed it to be a giant reptile, and in 1843 named it "king lizard": Basilosaurus in Greek. Scientists who later examined Basilosaurus, notably Richard Owen , realized the error.

Owen renamed the fossil Zeuglodon, meaning "yoked tooth"  a more appropriate description of the double-rooted molars of this animal. However, under the rules that govern naming species, the earliest name for a species has priority, even if that name is not an accurate description. Its name aside, Basilosaurus (skull at left) is significant because it is known to have retained small but well-developed hind limbs that projected from the body, although there was no joint between the pelvic bones and the vertebrae. Living whales retain only tiny splint-like bones as remnants of the pelvis and hind limbs. Basilosaurus has been found in Eocene rocks of the southeastern United States, notably in Alabama, Mississippi, and Louisiana  in fact it is the state fossil of Alabama, and the "state co-fossil" of Mississippi along with Zygorhiza. Basilosaurus has also been found in Eocene rocks of Australia and Egypt. The Rise of Modern Whales By the late Oligocene , the two modern lineages of cetaceans had evolved from archaeocete ancestors.

Interestingly, the late Oligocene whale Aetiocetus, from Oregon, has skull and jaw features typical of baleen whales, and is considered to be the earliest mysticete  yet it also bore a full set of teeth. By the Miocene , whales of both lineages are relatively common fossils in many marine deposits. A number of modern-day families of both toothed and baleen whales are known to have evolved by the late Miocene. These include the baleen whale families Balaenopteridae (rorqual whales, including the blue whale) and Balaenidae (right whales), and the toothed whale families Delphinidae (dolphins and killer whales), Physeteridae (sperm whales), Monodontidae (belugas and narwhals), Phocaenidae (porpoises), and Ziphiidae (beaked whales). Shown at right is the partial skull of a porpoise from the Miocene-age Monterey Formation , exposed at Duxbury Reef in Marin County, northern California. Researcher J.G.M.

Thewissen has an excellent set of pages on the origin of whales, and fellow researcher Mark Uhen maintains another fine page on early whale fossils and evolution . Primitive Eocene Whales has information on archaeocetes from the southeastern United States. There is also a brief exhibit on fossil whales at the University of Oslo. Paleontologists might also visit the special exhibit on "Charlotte" , a late Pleistocene fossil beluga whale from Vermont. For more information on living whales and where to see them, visit the Whale Watching Virtual Library , the Whale Conservation Institute , or the Cetacean Society International . An extensive species-by-species listing of WWW resources on whales and other marine mammals is also available as part of the Protected Marine Species project. And check out the work of UCMP scientists Healy Hamilton and Allen Collins on the evolution of river dolphins . Sources: Carroll, R.L. 1996. Patterns and Processes of Vertebrate Evolution. Cambridge University Press, Cambridge. Feldhamer, G.A., L.C. Drickamer, S.H. Vessey, and J.F. Merritt. 1999. Mammalogy: Adaptation, Diversity, and Ecology. McGraw-Hill, Boston.

Gingerich, P.D., S.M. Raza, M. Arif, M. Anwar, and X. Zhou. 1994. New whale from the Eocene of Pakistan and the origin of cetacean swimming. Nature 368:844847. Slijper, E.J. 1979. Whales. 2nd ed. Cornell University Press, Ithaca, New York.

Question: Which animals make up the mammalian order cetacea?
Answer: WHALES,