thick fur, each hair = hollow to trap air for better insulation
- hairs function like fiber-optic cables by channeling sunlight to animal’s dark/black skin that absorbs heat from sunlight
large teeth
sharp claws
diet = seals

walruses = large bodies, and adults (both male and female) have ivory tusks up to 1m long

tusks used for territorial fighting, hauling themselves onto iceberges, and stabbing prey

seals differ from sea lions and fur seals in these ways:

seals lack prominent ear flaps
seals have smaller and less prominent front flippers
seals have prominent claws extending from fore slippers
seals have diff hip structure —> can’t move rear flippers under their bodies
seals don’t move on land very well, can only slither along
seals propel themselves through water using a back-and forth motion of rear flippers whereas sea lions and fur seals flap large front flippers

Order Sirenia

includes manatees, dugongs = “sea cows”

manatees concentrated in coastal areas of tropical Atlantic and dugongs in tropical regions of Indian and W Pacific Oceans

characteristics of both:

both have paddle-like tail and rounded front flippers
bodies covered w/ sparse hairs which are concentrated around the mouth
large animals
land-dwelling ancestors were elephant like

sirenians only eat shallo-water coastal grasses = only vegetarian marine mammals

spend most of life in coastal waters heavily used by humans for commerce, recreation, development, and waste disposal —> major concern = habitat destruction

Order Cetacea

includes whales, dolphins, porpoises. cetacean body is cigar-shaped and insulated w/ thick layer of blubber

cetacean forelimbs modified into flippers thta move only at shoulder joint
hind limbs are vestigial, not attached to rest of skeleton, and usually not visible externally

all cetaceans share these characteristics:

elongated skull
blowholes on top of skull
very few hairs
horizontal tail fin = fluke used for propulsion by vertical movements

Modifications to Increase Swimming Speed

Cetaceans’ muscles not more powerful than other mammals so ability to swim fast results from modifications reducing frictional drag

streamlined body and they improve flow of water around their bodies w/ a specialized skin structure: skin consists of outer layer that’s 80% water and has narrow canals filled w/ spongy material, and a stiffer inner layer composed mostly of tough connective tissue

soft layer decreases pressure differences at skin-water interface by compressing when pressure is high and expanding when pressure is low, reducing turbulence and drag

Modifications to Allow Deep-Diving

Oxygen Usage

(1) inhaled air finds its way to tiny terminal chambers, the alveoli

alveoli are lined w/ a thin alveolar membrane that’s in contact w/ a dense bed of capillaries
exchange of gases between inhaled air and blood occurs across alveolar membrane

take one to three breaths per minute while resting = hold inhaled breath much longer —> can extract almost 90% oxygen in each breath whereas terrestrial mammals extract only 4-20%

cetaceans store and limit use of oxygen, which is possible bc they have a large blood volume per unit body mass

some cetaceans have 2x as many red blood cells per unit of blood volume and up to 9x as much myoglobin in muscle tissue as terrestrial animals —> large supplies of oxygen stored chemically in hemoglobin w/ in red blood cells and in myoglobin w/in muscles

Muscular Adaptations

cetaceans’ muscles are well adapted for deep dives:

muscle tissue is relatively insensitive to high levels of CO2 which builds up in the body through respiration, especially during deep dives
muscles can continue to function through anaerobic respiration when oxygen becomes depleted

research has shown that cetaceans’ swimming muscles can still function during a dive, even in the absence of oxygen, suggesting these muscles and other organisms may be sealed off from arteries —> circulatory system only services heart and brain —> reduced heart rate of 20-50% normal because of the decreased circulatory requirements

Do Cetaceans suffer from the effects of deep diving?

one difficulty with deep and prolonged dives is the absorption of compressed gases into the blood. when humans dive using compressed air (including nitrogen and oxygen) the higher pressure at depth causes more nitrogen to be dissolved in a diver’s body —> nitrogen narcosis (rapture of the deep)

nitrogen narcosis effects: similar to drunkenness and can occur when a diver either goes too deep or stays too long at depths greater than 30m

another difficulty can occur when divers return to the surface too rapidly —> decompression sickness (the bends)

during rapid ascent, the lungs cannot remove excess gases from the bloodstream fast enough, and the reduced pressure causes small bubbles of nitrogen to form in a diver’s blood and tissue
it’s like bubbles that form in a carbonated beverage when the container opens
bubbles interfere with blood circulation and can cause bone damage, excruciating pain, severe physical debilitation, or even death

debilitating effects of deep diving minimized in cetaceans bc they have collapsible rib cages:

by time cetacean has reached depth of 70m, its rib cage has collapsed under pressure
- lungs within rib cage also collapse, removing all air from alveoli —> prevents the blood from absorbing additional gases across the alveolar membrane, minimizing nitrogen narcosis

cetaceans may be naturally resilient to the buildup of nitrogen gas in their bodies. in a study where enough nitrogen was put into the tissue of a dolphin to give a human a severe case of the bends, dolphin appeared to suffer no ill effects. this suggests that dolphins may have simply evolved an insensitivity to the buildup of excess nitrogen gas.

Suborder Odontoceti

members of order cetacea can be divided into two duborders:

odontoceti and mysticeti

suborder odontoceti includes:

dolphins
porpoises
killer whales
sperm whales

Characteristics of Toothed Whales

all toothed whales have prominent teeth that are used to hold and position fish and squid to facilitate swallowing them whole. killer whales, however, are known to feed on a variety of larger animals, including other whales.

toothed whales form complex and long-lived social groups. a toothed whale has one external nasal opening while a baleen whale has two

both toothed and baleen whales can emit and receive sounds, the ability to use sound is best developed in toothed whales

Differences between Dolphins and Porpoises

dolphins and porpoises are small toothed whales of suborder odontoceti

they have similarities in appearance, behavior, and range and are so easily confused
for instance, both dolphins and porpoises can exhibit a behavior known as “porpoising” which is leaping out of the water while swimming, however there are several morphological diffefences between dolphins and porpoises

porpoises = smaller and more stout body shape than dolphins, which are more elongated and streamlined

generally porpoises have a blunt snout while dolphins have a longer rostrum
porpoises have a smaller and more triangular dorsal fin, whereas a dolphin’s dorsal fin is sickle-shaped or falcate and appears hooked and curved backward in profile view

dolphins and porpoises also have differences in the shape of their teeth, although it’s often difficult to get close enough to see them. the teeth of dolphins end in points, while teeth of porpoises are blunt or flat and resemble our incisors (front teeth)

killer whales have teeth ending in points —> dolphin family

Echolocation and Hearing in Toothed Whales

toothed whales don’t have vocal chords but can produce a variety of sounrds

echolocation: to locate object and determine its distance, toothed whales send sound signals through the water, some of which are reflected from various objects and are returned to the animal and interpreted
- sound penetrates objects —> echolocation can produce a three-dimensional image of object’s internal structure and density

sound generation is different in different species:

Ex. sperm wahels - sounds generated when whale forces air through its right nasal passage to special structure called museau du singe, they snap shut to produce a percussive sound

click travels through the skulland is amplified into water
they can aim their clicks

Ex. small toothed whales i.e. dolphins and porpoises - sounds emitted from phonic lips near blowhole

contractions of muscles produce a wide variety of complex sounds such as clicks, buzzes, and whistles
soudns are concentrated as they pass through an organ that sits atop skull called melon, which can be manipulated by the animal and focuses sounds
they can pick out schools of fish and individual fish

how do toothed whales hear underwater?

toothed whales have specialized fats associated w/ their jaws that efficiently convey sound waves from the ocean to their ears
these structures insulate inner ear housing from rest of the skull, allowing them to differentiate sounds they ehar underwater
in some, sounds are picked up by thin jawbone and passed to inner ear via fat-filled body

growing concern that noise pollution in ocean is affecting cetaceans coming from boats

How Intelligent are toothed whales?

can communicate w/ each other using sound
have large brains relative to their body size
brains are highly convoluted (similar to other intelligent species)
some wild dolphins been reported to assist drowning humans in the ocean
some dolphins been trained to respond to hand signals and do tricks on command

remarkable abilities don’t necessarily imply high intelligence

Suborder Mysticeti

c=baleen whales = largest whales, blue whale, finback whale, humpback whale, gray whale

baleen whales >> in size than toothed whales bc of differences in food sources. baleen whales eat lower on food web including zooplankton which are abundant

Use of Baleen

to concentrate small prey items and separate them from seawater, baleen whales have parallel rows of baleen plates in their ouths instead of teeth

baleen plates hang from whale’s upper jaw
baleen made of flezxible keratin, can be 4.3m long

to feed, largest baleen whales fill mouths w/ body-weight of water and prey, allowing pleated lower jaw to balloon in size

whales force water out between fibrous plates of baleen, trapping small fish, krill, and plankton inside mouths
feed at or near surface, sometimes working together to produce a circular curtain of bubbles to concentrte prey

Baleen Whales and Sounds

baleen whales produce sound but at lower frequencies than toothed whales

Baleen Whale Families

baleen whales grouped into following 3 families:
(1) gray whale: short, coarse baleen, no dorsal fin, only two to five ventral grooves on lower jaw. it’s a bottom feeder

(2) rorqual whales: short baleen, many ventral grooves

feed by gulping large mouthfuls of water containing small food items
- balaenopterids: long slender bodies, small sickle-shaped dorsal fins, flukes with smooth edges (blue whales)
- megapterids: more robust body, long flippers, flukes w/ uneven trailing edges, tiny dorsal fins, nodules or tubercles on head (humpback whales)

(3) right whales: long, fine baleen, broad traingular flukes, no dorsal fin, no ventral grooves

RECAP

marine mammals include orders Carnivora (sea otters, polar bears, and pinnipeds - walrus, seals, sea lions, and fur seals), Sirenia (manatees and dugongs), and Cetacea (whales, dolphins, and porpoises)

CONCEPT CHECK 14.4

(1) What common characteristics do all organisms in class Mammalia share?

(2) Describe marine mammals within the order Carnivora, including their adaptations for living in the marine environment.

(3) How can true seals be differentiated from the eared seals (sea lions and fur seals)?

(4) Describe the marine mammals within the order Sirenia, including their distinguishing characteristics.

(5) How can dolphins be differentiated from porpoises?

(6) Describe differences between cetaceans of the suborder Odontoceti (toothed whales) with those of the suborder Mysticeti (baleen whales). Be sure to include examples from each suborder.

(7) Compare echolocation systems in sperm whales and dolphins. Evaluate the differences and similarities between the two systems.

(8) Describe the mechanism by which baleen whales feed.

Note