W8: Evolution/MarineMammalAdaptations

*________* are mammals - they have mammary glands to produce milk for their offspring and they have hair. In *________* the hair is limited to their rostrum (see biology), developing in the womb and lost soon after birth with the exception of the Botos *________* of the Amazon which retain sensory whiskers throughout their lives.

*Dolphins*

The first Sirenians appeared in the early Eocene in Europe, but by the close of this epoch, they had spread to tropical Asia and North America. *_______* were the prevalent group in the Caribbean and Mediterranean until the Late Miocene, when all but the Indo-Pacific species went extinct. Subsequently, the manatees of South America entered these areas in the Pliocene.

*Dugongs*

*______ _______* include the *Order Cetacea* (porpoises and whales), the *Order Carnivora* (animals like seals), and the *Order Sirenia* (dugongs, manatees and sea cows).

*Marine mammals*

Within a mere million years Ambulocetus had evolved from the *__________*. This walking whale was larger - about the size of a large male sea lion. With large front limbs, small back limbs, a muscular tail, a long snout and side facing eyes it may have resembled a crocodile in appearance

*Pakicetids*

*_________* feed in cold currents at high latitudes during the summer, mostly on the eastern sides of the oceans. Some species range mostly offshore, others are more often found in coastal waters. Their food is primarily krill, euphausiid crustaceans, which congregate near the surface in cold water.

*Rorquals*

*___-____* are herbivores that graze on sea-grasses and related plants, though some will eat algae and floating monocots, such as Pistia and Eichhornia, and they will occasionally eat shellfish and dead fish. Adults may eat as much as 30 pounds of food a day, and may reach more than 500 kg.

*Sea-cows*

To retain warmth, marine mammals have *____________* such as the reduction of surface area and the increase in internal volume, a fatty layer of blubber under very thick skin, and a reduction in the amount of blood going to areas in contact with the cold water.

*adaptations*

The reduction of the *_______ _____* is an important evolutionary step as, in modern cetaceans, it stops them overstimulating their *_______ ______s* while executing their aquatic acrobatics. It is quite possible that the Remingtonocetidae would have resembled an enormous long-snouted otter with a powerful swimming tail.

*balance organ*

Unlike the Remingtonocetidae, the *Protocetids* had large eyes giving them excellent vision. Furthermore, unlike the Pakicetids and Ambulocetus the Protocetids' large eyes were located on the side of their heads around the midline of the skull. Nasal drift in Protocetids marked the movement of the nasal opening back from the tip of the snout - the first step towards the *_________* located on the heads of modern cetaceans.

*blowholes*

The 'flipper' shaped forelimbs were an important evolutionary feature, the webbed hand without visible digits and an elbow joint that was not separately mobile were very much like modern *__________* while the tiny hind-limbs can still sometimes be seen in modern *___________* with atavisms.

*cetaceans*

Blue whales eat little but *___________*; other species have a broader diet, even including some fish. During the fall, most species migrate toward equatorial latitudes. They fast for several month, living by metabolizing blubber.

*euphausiids*

Marine mammals are also able to dive very deep into the water without getting the bends because as they dive down deeper they *exhale* instead of inhale like we do. They expel air from their lungs, and therefore do not absorb excess nitrogen

*exhale*

Around 41 million years ago, *Basilosauridae* came to the fore. With its blowhole, *_______* forelimbs and fluked tail it was recognizable as what we now think of when discussing cetaceans. While the different genera of Basilosauridae varied they can be grouped into two distinct body types - long snake-like bodies and shorter dolphin-like bodies.

*flipper*

Some baleen whales, most famously the *________ ______*, 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.

*humpback whales*

Dolphins and porpoises are examples of *___________*, as are belugas, narwhals, killer whales, sperm whales, and beaked whales.

*odontocetes*

One fundamental difference between cetaceans and fish is the *____*. The *____s* of mammals are horizontal enabling to swim both vertically and horizontally. The *____s* of most fish are vertical, so the swimming motion is side to side.

*tail*

*Archaeocetes*

-Ancient whales. -Had different types of teeth. -Had rostral nostrils instead of a blowhole. -Some had substantial hind limbs.

*Basilosaurus*

-Mammals that returned to the seas as the top marine carnivores of the Eocene. -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.

*Cetacea*

-Whales, dolphins, porpoises. -Most dolphins are marine, some are freshwater. -Whales have streamlike bodies with highly compressed neck vertebrae, dorsal fins, and a tail with two finlike flukesarranged 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.

Other adaptations to marine living include:

A slower heartbeat during dives, reduced blood flow to non-vital organs, unusually high hemoglobin count in blood, and an unusually high myoglobin count in muscles.

_______ whales lack teeth completely as adults (although teeth are present in fetal _______ whales). They feed by straining small marine organisms out of the water using plates of _______, a hornlike substance that forms filaments that hang down from the roof of the mouth.

Baleen

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).

Mysticetes

Baleen whales; these are the biggest whales; blue whale is biggest animal ever to have lived in earth

Balaenopteridae (rorquals)

The largest group of baleen whales, a family with nine extant species in two genera. They include what is believed to be the largest animal that has ever lived, the blue whale, which can reach 180 tonnes (200 short tons), and the fin whale, which reaches 120 tonnes (130 short tons); even the smallest of the group, the northern minke whale, reaches 9 tonnes (10 short tons).

The skulls of these *mysticetes* can be recognized by a combination of the following technical characteristics:

The nasals and the nasal processes of the premaxillae extend backward beyond the supraorbital processes of the frontals; the nasals are reduced in size; the frontals are small and barely or not exposed on the dorsal surface; the supraoccipital extends forward beyond the zygomatic process of the squamosal; the rostrum is broad and flat.

Pakicetids were about the size of a goat and had wolf like features with four limbs and a tail. They lived an __________ lifestyle - hunting for food while wading in shallow freshwater streams, rivers and lakes.

amphibious

Most fish will move their tail from side to side so that water is pushed _________ and around the side and the fish moves forward. Fins at the side of the fish help counteract the tendency of the head to swing from side to side as the tail moves.

backwards

The _______ plates of *rorquals* are short and broad. These species feed by gulping large quantities of water and straining crustaceans and fish by shooting the water out between the _______ plates.

baleen

Dolphins are also ____________ distinct - often being more vocal than their relatives. In total there are 43 currently recognized species of dolphins - 38 marine species and 5 riverine species.

behaviorally

Ambulocetus was better adapted to amphibious life and lived in and around the ________ waters of estuaries and the shallow seas of coastal swamps and forests. It likely used its rear limbs and tail in an otter like swimming fashion and was unlikely to be fast moving.

brackish

The streamlined shape observed in both marine fish and marine mammals is an example of biological ____________.

convergence

Modern whales arose around 34 million years ago when the *Neoceti* (the Odontocetes or toothed whales and Mysticetes or baleen whales) appeared. It is in this period of time that the *Odontocetes* developed *_____________* to hunt using sound and Mysticetes developed the baleen plates in their mouths to filter feed allowing them to forage for prey in bulk.

echolocation

*Sirenians* are slow and passive mammals of tropical and sub-tropical waters. Their large thick bodies betray their heritage as relatives of __________.

elephants

Remingtonocetidae also had an enlarged _______ running the full length of their lower jaw, in modern cetaceans these long _______ support a fatty pad that transmits sound to the middle ear and allows them to hear more clearly underwater.

foramen

Rorquals are usually seen in ______ ("pods") of 2-5 individuals. Their populations have been much reduced by whaling, and most are now fully protected by international treaty.

groups

By 48 to 41 million years ago the *Remingtonocetidae* had developed. Like Ambulocetus they had long snouts but their teeth, _______, eyes, sense of balance and mode of swimming had changed. Their eyes were reduced for life adapted to poor visibility in muddy bays fed by heavily-silted rivers and their sense of _______ had improved to compensate.

hearing

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 ______ mammals. In fact, some fossil teeth that were once identified as mesonychids are now known to have come from archaeocetes.

hoofed

Fish also have fins on their back, their sides and underneath their bodies. Fish, whales, turtles and even seals have specialized _____ for swimming.

limbs

All ______ dolphins are grouped under the family *Delphinidae* and the riverine dolphins belong to the Platanistidae and Iniidae families.

marine

Odontocetes bear teeth — typically numerous and ___-____, although sometimes modified, as in the single tusk of the narwhal or the odd, fanglike lower teeth of the beaked whales.

peg-like

Dolphins are distinct from _________ and toothed whales due to their rostrums, lean bodies, cone-shaped teeth and curved dorsal fins (though not all dolphins have all of these features).

porpoises

Most of the ______ generated for swimming in marine animals comes from the tail at the back.

power

Ancient *Rodhocetus* had well-developed hind limbs, but unlike land mammals, Rodhocetus did not have its vertebrae in the pelvic region fused together into a _______.

sacrum

The diversity of Protocetids means that some of them would have had ____-____ lifestyles, hunting in the water but mating, birthing and nursing on land while others seem to have been obligate marine animals. They probably swam using a combination of paddling with their hind limbs and dorsoventral (up/down) undulations of their tails.

seal-like

There are only five living species of _________, known collectively as "sea-cows," including the dugong and the manatees.

sirenians

Sirenians are _________ creatures, who come together only to mate, or when favorable local conditions attract individuals for a short time. They may live more than 70 years.

solitary

The rounded head and tapering body shape allows marine fish and mammals to glide smoothly through the water, wasting little energy due to resistance. Animals that are not ___________, like the stingray or the globefish, have sacrificed efficient swimming for benefits of camouflage or body armor.

streamlined

Alongside whales and porpoises, dolphins make up the order *Cetartiodactyla.* Their _____ make them part of the suborder Odontoceti along with porpoises and toothed whales.

teeth

*Cetaceans* began to emerge around 50 million years ago, in the middle Eocene, around northern Pakistan and western India. The first *cetacean* looked nothing like the ______, dolphins and porpoises we recognize today.

whales