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The cetacean is a marine mammal family which includes whales, dolphins, and porpoises. Although cetaceans are aquatic, cetaceans are mammals, this means that whales, dolphins and porpoises are warm blooded, give birth to live young, nurse young, have traces of hair or fur, and must come to the surface to breathe air through the lungs. Cetaceans are separated into two subspecies, Odontoceti (toothed mammals) and Mysticeti (baleen mammals).

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There are two suborders of cetacea odontoceti, toothed mammals, and  Mysticeti, baleen mammals.
Odontoceti contain the  Delphinidae,  Phocoenidae,  Physeteridae  and  Platanistidae families. Mysticeti contain the  Balaenidae,  Balaenopteridae,  Eschrichtiidae and Neobalaenidae families.

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Internal & External Characteristics
External : Cetaceans have a  streamlined body shape, paddle-shaped front limbs, vestigial hind limbs, no external digits or claws, tail flattened laterally and bearing horizontal flukes at the tip and external blowhole(s)  on the top of the head.

Internal : Cetaceans have vestigial ear pinnae, thick subcutaneous blubber layer filled with fat and oil, telescoped skull bones, addition of compressed vertebrae, shortening of the neck, lack of sweat glands,  3-chambered stomach and an airway reinforced with cartilage to the alveoli.

Many of these characteristics are adaptations to reduce drag for fast swimming in an aquatic environment.

Behavioral Characteristics
Cetaceans are social animals who form large or small pods, or some are found in pairs or  singles. A group of cetaceans that normally feed and travel together is called by various names, school, herd, pod. Many cetaceans exhibit epimeletic behavior, which means healthy animals take care of animals that has become temporarily incapacitated. Migration patterns and reproduction depend on the species of cetacean. Cetacean breeding is seasonal, usually in the winter, and females normally calve once every two years. As mammals, they reproduce by internal fertilization. Females carry the fetus for about a year, then give birth tail first, opposite of most terrestrial mammals. Cetaceans are not strictly diurnal or nocturnal. Cetaceans perform many tricks such as breaching, bow riding, flippering, lob-tailing, logging, spouting and spyhopping. Cetaceans have different forms of communication which include clicks, grunts, whistles, calls and songs.

Habitat Characteristics
Cetaceans inhabit all of the world's oceans, as well as some freshwater lakes and rivers in South America, North America, and Asia. Species, such as Orcas (killer whales) are found in all of the world's oceans. Others are limited to one hemisphere or ocean, still others have highly restricted ranges.

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Megaptera novaeangliae

me-gap-te-ra noh-vee-ang-li-ee

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Found in all the world's oceans, most populations of humpback whales follow a regular migration route, summering in temperate and polar waters for feeding, and wintering in tropical waters for mating and calving.
Fun Fact - In the Arabian Sea, a year-round non-migratory population of humpbacks appears not to follow this general rule.

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Physical Description
The head of a humpback whale is broad and rounded when viewed from above, but slim in profile. The body is not as streamlined  but is quite round, narrowing to a slender peduncle (tail stock). The top of the head and lower jaw have rounded, bump-like knobs, each containing at least one stiff hair. The purpose of these hairs is not known, though they may allow the whale to detect movement in nearby waters. There are between 20-50 ventral grooves which extend slightly beyond the navel.

Color
The body is black on the dorsal (upper) side, and speckled black and white on the ventral (under) side, this color pattern extends to the flukes. This pattern is distinctive to each whale. The flippers range from all white to all black dorsally, but are usually white ventrally.

Fins and Flukes
About 2/3 of the way back on the body is an irregularly shaped dorsal (top) fin. Humpback's flippers are very long, between 1/4 and 1/3 the length of its body, and have large knobs on the leading edge. The flukes (tail), which can be 18 feet wide, is serrated and pointed at the tips.

Weight and Length
Adult males measure 40-48 feet, adult females measure 45-50 feet. Humpbacks weigh 25 to 40 tons.

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Feeding
Humpbacks are baleen whales which means they filter their food through baleen plates. They consume krill, anchovies, cod, sardines, mackerel and others sorts of schooling fish.

Breeding and Mating
Each female typically bears a calf every 2-3 years and the gestation period is 12 months. Singing whales are males may be a part of mating behavior.

Communication and Social
Humpbacks can throw themselves completely out of the water (breaching), and swim on their backs with both flippers in the air. They also engage in "tail lobbing" (raising their huge flukes out of the water and then slapping it on the surface) and "flipper slapping" (using their flippers to slap the water). It is possible that these behaviors are important in communication between humpbacks. Perhaps the most interesting behavior of humpback whales is their "singing." Scientists have discovered that humpback whales sing long, complex "songs". Whales in the North American Atlantic population sing the same song, and all the whales in the North American Pacific population sing the same song. However, the songs of each of these populations and of those in other areas of the world are uniquely different. A typical song lasts from 10-20 minutes, is repeated continuously for hours at a time, and changes gradually from year to year.

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Orcinus orca

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The Orca is found in all the oceans of the world, though they are more abundant in cooler waters. Unlike other species of cetaceans, which follow a regular migration route each year, the Orca seems to travel according to the availability of food. Orcas are one of the few species of cetaceans that move freely from hemisphere to hemisphere.

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Physical Description
The Orca has a striking color pattern made up of well-defined areas of shiny black and cream or white. The dorsal (top) part of its body is black, with a pale white to gray "saddle" behind the dorsal fin. It has an oval, white eye patch behind and above each eye. The chin, throat, central length of the ventral (underside) area, and undersides of the tail flukes are white. Each whale can be individually identified by its markings and by the shape of its saddle patch and dorsal fin.

Fins and Flukes
Orca's dorsal fin can reach six feet high in males and is shaped like an isosceles triangle. The immature male and the female dorsal fins are also large, reaching 3 feet high, but are curved. The dorsal fin often has identifying nicks, cuts, scars and indentations. The paddle-shaped pectoral flippers are broad, rounded, and can reach a length of nearly six feet and a width of three feet.

Weight and Length
Males can grow as large as 32 feet long and weigh eight to nine tons. Females can reach 23 feet in length and weigh up to four tons.

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Feeding
The mouth of the Orca is large and well adapted for hunting. It has 46 to 50 conical shaped teeth that point slightly backwards and inwards. The upper and lower teeth interlock, which aids in gripping large prey and tearing it into smaller pieces for easier swallowing. Depending on the population and geographic area, the diet of Orcas varies. Orcas generally eat sea lions, elephant seals, harbor seals, porpoises, squid, sharks, fish, penguins, smaller whales, such as belugas and narwhals and even large baleen whales, such as gray whales.

Breeding and Mating
Little is known about the Orca's breeding habits. Newborn calves have been observed throughout the year suggesting that that mating can occur at any time with no particular breeding season. In the wild, Orcas become sexually mature between the ages of ten and eighteen years of age and are thought to be actively reproducing by the time the male reaches about 20 feet in length and the female reaches about sixteen feet.

Communication and Social
Orcas generally live in pods (groups) consisting of several females, calves, one or more males, and/or juveniles. Some pods consist of a mother and her offspring who stay with her for life. Each pod has some sounds in common with other pods, and other sounds that are unique to its own pod. Orcas produce sounds for two overlapping functions, communicating and navigation.

Orcas produce whistles, echolocation clicks, pulsed calls, low-frequency pops, and jaw claps. Some behaviors, such as head-butting and jaw-snapping, are usually assumed to communicate aggression. The purpose of other behaviors, including breaching and pec-slapping, is not clearly understood.

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Lagenorhynchus obliquidens

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The Pacific White-Sided Dolphin inhabits temperate, coastal waters in the North Pacific, avoiding both tropical or Arctic waters. Its range extends from Amchitka Island in the Aleutians, to the Gulf of Alaska south along the coast of North America to the tip of Baja California. It is also found off the coast of Asia from the Kuril Islands to Japan. It is abundant in Japanese waters with estimates of 30,000 to 50,000 in that area.

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Physical Description
The Pacific white-sided dolphin has a short, rounded, thick beak containing 23 to 32 small, rounded slightly curved teeth in each side of the upper and lower jaws.

Color
The Pacific White-Sided Dolphin is attractively marked. Its back is black and its sides are light gray with thin, white stripes that extend from above the eye along the sides, widening towards the tail; its belly is white. It has a black beak and lips and a black ring around each eye.

Fin and Flukes
Its dorsal fin is tall and sharply hooked, and is located at the center of the back. The leading edge is black and the rear portion is light gray. Its flippers are small and curved and rounded at the tips. Its flukes are notched in the center.

Weight and Length
These dolphins reach a length of seven to eight feet and weigh 300 pounds.

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Feeding
Pacific White Sided Dolphins eat squid and small schooling fish such as anchovies, herring, sardines, and hake. It is believed they hunt largely at night.

Breeding and Mating
Sexual maturity for both sexes is reached when they are six feet in length, but this can vary according to geographical location.

Communication and Social
Pacific White-Sided dolphins are often found in large herds of 90 to 100. The herds are made up of animals of both sexes and all ages. Since they share the same range, they are most commonly seen with Northern Right-Whale dolphins and are often seen accompanying other dolphins and large whales. These dolphins communicate through the use of high-pitched whistles and physical contact. Each dolphin has a unique frequency that they communicate in which allows pods to determine which dolphin is communicating with them. While it is difficult to interpret what each series of clicks and whistles means it is assumed that these dolphins use vocalization to communicate to one another that they have found nearby food, that there may be an incoming threat, that they have a desire to mate and to locate other pod members within their group.
Physical contact may be used to communicate affection, attention, threats or aggression depending on the strength of the contact and body language of the dolphin.

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Animalia
All cetaceans are members of the kingdom Animalia. The kingdom of  Animalia does not contain prokaryotes or protists. All members of Animalia are multicellular and all are heterotrophs.

Chortada
Animals in the phylum Chordata share four key features that appear at some stage during their development, a notochord, a dorsal hollow nerve cord, pharyngeal slits and a post-anal tail.

Mammalia
All animals in the class of mammalia are vertebrates, endothermic (warm-blooded), have hair on their bodies and produce milk to feed their babies.

Cetacea
All memebers of the cetacean order are completely aquatic, fusiform body, lack sebaceous glands, thick insulation, forelimbs (flippers, tail forms flukes), no external digits or claws, no mucous membrane  (smell), no outer visible ears, no vocal chords, modified skull, reduced differentiation of vertebrae and “pinhole camera” , type of eye.

Suborders of Cetacea
The suborders of cetacea are  odontoceti , toothed mammals, and  Mysticeti , baleen mammals.
Odontoceti contain the  Delphinidae,  Phocoenidae,  Physeteridae  and  Platanistidae families. Mysticeti contain the  Balaenidae,  Balaenopteridae,  Eschrichtiidae and Neobalaenidae families.

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Fossil Record
Fossils provide solid evidence that organisms from the past are not the same as those found today; fossils show a progression of evolution. The resulting fossil record tells the story of the past and shows the evolution of form over millions of years. The fossils of archaeocetes, prehistoric whales, provides evidence of walking whales. The fossil remains demonstrate the body transition from land to water. The oldest whale, Indohyus, was a land mammal during the Econe era. The Indohyus transforms throughout the Econe era into  different archaeocetes families such as, Remingtonocetidae, Protocetidae, and Basilosauridae. The bone structure of the archaeocetes demonstrate the transition from land to water.

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The skull of the Indohyus, the Indohyus is from the Eocene period

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The skull of Pakicetus inachus, the Pakicetus is from Eocene period, about 52 million years ago

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The skeleton of Ambulocetus natans, the Ambulocetus is from the early to middle Eocene, about 50 million years ago

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The skull of Rodhocetus kasrani, is from  the middle Eocene time period, 46-7 million years ago

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The skull of the Maiacetus, the Maiacetus is from the Eocene period

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The skeleton of the Basilosaurus , it's from the latest part of Eocene 35-40 million years ago

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https://www.google.com/url?sa=i&rct=j&q=&esrc=s&source=images&cd=&cad=rja&uact=8&ved=0ahUKEwiQtbXDqqzUAhWBbD4KHWT_AEsQjRwIBw&url=http%3A%2F%2Fwww.cms.int%2Fpacific-cetaceans%2Fen&psig=AFQjCNHqa6iC0g43PQ3GQMVunKBL8r-EDQ&ust=1496945390201802
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https://www.google.com/search?q=anatomy+of+toothed+whales&safe=strict&source=lnms&tbm=isch&sa=X&ved=0ahUKEwi45L6g0aTUAhVMwYMKHQEoCA0Q_AUICigB&biw=1366&bih=662#imgrc=3hXBnJ6Tma0ZtM:
https://www.google.com/search?q=anatomy+of+toothed+whales&safe=strict&source=lnms&tbm=isch&sa=X&ved=0ahUKEwi45L6g0aTUAhVMwYMKHQEoCA0Q_AUICigB&biw=1366&bih=662#safe=strict&tbm=isch&q=pylogenetic+tree+whales&imgrc=VCT_1hDYPWGHSM:
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http://stories.anmm.gov.au/whale-evolution/

https://c1.staticflickr.com/1/392/31498493094_3de89b6084_b.jpg
http://www.ucmp.berkeley.edu/mammal/cetacea/cetacean.html
https://www.google.com/search?q=maiacetus+fossil&safe=strict&rlz=1C1CHMO_enUS575US575&source=lnms&tbm=isch&sa=X&ved=0ahUKEwjnzpP7zZbUAhWPZiYKHaRhBP8Q_AUICigB&biw=1366&bih=662#imgrc=2FzHwTQ6U0956M:

https://www.google.com/search?q=humpback+whale+images&safe=strict&tbm=isch&tbo=u&source=univ&sa=X&ved=0ahUKEwiN0r3tvJvUAhUr7IMKHbqoCs0QsAQIIA&biw=1366&bih=662#imgrc=sGnhH8MoO7Co7M:
https://www.google.com/search?q=humpback+whale+images&safe=strict&tbm=isch&tbo=u&source=univ&sa=X&ved=0ahUKEwiN0r3tvJvUAhUr7IMKHbqoCs0QsAQIIA&biw=1366&bih=662#imgdii=rYS2jKo67ZhdqM:&imgrc=dFPGIxZ8wwJmDM:
https://www.google.com/search?q=killer+whale+photos&safe=strict&source=lnms&tbm=isch&sa=X&ved=0ahUKEwiA8e-KvZvUAhWG1IMKHXDxDX8Q_AUICigB&biw=1366&bih=662#imgrc=EjJTK9JXJY23wM:
https://www.google.com/search?q=killer+whale+photos&safe=strict&source=lnms&tbm=isch&sa=X&ved=0ahUKEwiA8e-KvZvUAhWG1IMKHXDxDX8Q_AUICigB&biw=1366&bih=662#imgrc=Bx_tIG4bBE6BaM:
https://www.google.com/search?q=pacific+white+sided+dolphin+underwater&safe=strict&source=lnms&tbm=isch&sa=X&ved=0ahUKEwjO-rfEvZvUAhUn8IMKHUXKAGEQ_AUICigB&biw=1366&bih=662#imgdii=auSx-uOj5D7dgM:&imgrc=AVmxs1B044ACHM:
https://upload.wikimedia.org/wikipedia/commons/f/f1/Pacific_white-sided_dolphins_%28Lagenorhynchus_obliquidens%29_NOAA.jpg

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Taxonomy Relatedness to Cetaceans
The taxonometric way of classifying organisms is based on similarities between different organisms. The Humpback whale, Orca and Pacific White Sided dolphin share the same taxonomic order and the Orca and Pacific White Sided dolphin share the same taxonomic suborder and family. The taxonomy of the Orca and Pacific White Sided dolphin clarify that the characteristics of the Orca and Pacific White Sided dolphin are more closely related than the Humpback whale.

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Biochemistry Evidence
Cetaceans have highly derived auditory systems adapted for underwater hearing.  Odontoceti whales receive sound through specialized fats associated with the lower jaws, leading to the ears.  These “acoustic fats” have unusual chemical compositions, comprised of endogenously synthesized short, branch-chained fatty acids and fatty alcohols within triacylglycerols and wax esters. These acoustic fats and hearing mechanisms in Odontoceti whales are relatively well-studied, however, not much is known about hearing in baleen whales. However, the discovery of a large, well-formed fat body which contacts the ears and ossicles of at least two baleen whale species, the minke whale (Balaenoptera acutorostrata)and fin whale (Balaenoptera physalus) may have similar “acoustic fats” to Odontoceti whales.

DNA or RNA Evidence
The sequence of the mitochondrial DNA (mtDNA) molecule of the blue whale was compared with the mtDNA of the fin whale. It was recently documented that the two species can hybridize and that male offspring are infertile whereas female offspring may be fertile. The present comparison made it possible to determine the degree of mtDNA difference that occurs between two species that are not completely separated by hybridization incompatibility.
Two species that have evolved from a common ancestor will have DNA that has very similar base pair sequences. The degree of relatedness of two species can be estimated by examining how similar their base pair sequences are. One method of assessing relatedness uses hybridization of DNA. In the molecular genetic technique of hybridization of DNA, single strands of DNA from two different species are allowed to join together to form hybrid double helices. These hybrid segments of DNA can be used to determine the evolutionary relatedness of organisms by examining how DNA base pair sequences are similar and dissimilar.

Chromosomal Evidence
Comparisons have been made between the karyotypes of the different species of cetaceans. All cetaceans so far studied have 22 chromosomes except the sperm and pygmy sperm whales, which have 21 chromosomes and karyotypes entirely different from those of the 22 chromosome species.  Although not all cetaceans have the exact number of chromosomes it is important that the cetaceans have the same range of chromosomes so that they can continue to reproduce and do not become sterile. The structure of chromosomes are sometimes mutated during the process of meiosis, for example chromosomes are missed, duplicated, fussed or added which cause the organism to have different features than originally planned. The change of chromosomes can show the change of organisms overtime, known as evolution.

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Type of Speciation and Evolution
Cetaceans gradually evolved over a long period of time. Modern cetaceans began to evolve 50 million years ago and only evolved every ten to twenty million years. Cetaceans are an example of convergent evolution. Cetaceans began as land mammals and evolved into aquatic mammals to be better adapted to their environment.

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Evolutionary Mechanisms

Microevolution
Among mammals, modern cetaceans do not have hind limbs. However, cetacean embryos do initiate hind-limb bud development. In dolphins, the bud arrests and degenerates around the fifth gestational week. Initial limb outgrowth in amniotes is maintained by two signaling centers, the apical ectodermal ridge (AER) and the zone of polarizing activity (ZPA). Data indicates that cetaceans hind-limb bud forms an AER and that this structure is expresses but the expression is maintained. Sonic hedgehog (Shh), which mediates the signaling activity of the ZPA, is absent from the dolphin hind-limb bud. The  failure to establish a ZPA is associated with the absence of Hand2, an upstream regulator of Shh. Interpreting the results  of both the cetacean fossil record and the known functions of Shh suggests that reduction of Shh expression may have occurred 41 million years ago and led to the loss of distal limb elements. The total loss of Shh expression may account for the further loss of hind-limb elements that occurred near the origin of the modern suborders of cetaceans 34 million years ago. Integration of paleontological and developmental data suggests that hind-limb size was reduced by gradually operating microevolutionary changes.

Genetic Drift
New discoveries of cetaceans genetics found whale-specific mutations in genes important for the regulation of salt and of blood pressure and for antioxidants that get rid of charged oxygen molecules that can harm cells. These molecules increase in number as the whale uses up its oxygen supply during dives.Comparative genomic analysis identified an expansion in the whale ancestry of genes associated with stress-responsive proteins and anaerobic metabolism, whereas ancestry genes related to body hair and sensory receptors were contracted. Whale-specific mutations in genes encoding antioxidants and enzymes controlling blood pressure and salt concentration were identified during the investigation of cetaceans genes. Overall the whale-genome sequences exhibited distinct features that are associated with the physiological and morphological changes needed for life in an aquatic environment, marked by resistance to physiological stresses caused by a lack of oxygen, increased amounts of reactive oxygen species and high salt levels. As cetaceans evolved genes were altered for the aquatic environment.

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Orca Karyotype (Odontoceti)
Orca's have 44 chromosomes. The top image is a male Orca karyotype and the bottom image is a female Orca karyotype

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Sei Whale Karyotype  (Mysticeti)
Sei whales have 44 chromosomes, the image is a male Sei whale karyotype

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Darwin's theory consisted of two main points, diverse groups of animals Darwin's theory of evolution, also called Darwinism, can be further divided into 5 parts, common descent, gradualism, population speciation, and natural selection.

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Cetaceans taxonomic group are an example of Darwin's two theories of evolution. Cetaceans come from the same ancestors, which is proven through fossil records, DNA or RNA evidence and the comparison of chromosomes. Cetaceans are example of genetic drift and microevolution, which are evolutionary mechanisms. Cetaceans represents Darwin's two theories of evolution because they evolve from one or a few common ancestors and they demonstrate mechanisms by which this evolution takes place is natural selection.

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Anatomy of Mysticeti

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Anatomy of Odontoceti

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Descent with modification means that traits are passed down from generation to generation and sometimes undergo changes or modifications over time, cetaceans passed down similar traits from generation to generation and theses traits had minor altercations.

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Disruptive selection increases genetic variance when natural selection selects for two or more extreme phenotype that each have specific advantages. Cetaceans began to favor fins, flukes and almost completely hairless bodies because the traits were better adapted for their environment.