Cetacea

Cetacea

I. Introduction

A. Fully adapted for aquatic life

B. Success of Cetaceans

1. Swimming and diving ability

2. Capability of many to echolocate (Odontoceti)

3. Considerable intelligence

4. Complex social behavior

C. All species are list in appendix I or II of Convention on International Trade in Endangered

Species

II. Taxonomy

A. Archaeoceti

1. Fossils found in association with land mammals

2. Derived from primitive carnivorous or scavenging ungulates → Artiodactyla

3. Two genera are known to have had legs

4. Provide remarkable example of major evolutionary transition

a. From land to water

b. Changes in osmoregulatory abilities due to shift from fresh to salt water

B. Cetacea form a monophyletic group

C. Relationships within order remain in debate

D. Two suborders → 11 families

1. Based on type of feeding mechanism

a. Mysticeti → baleen plates; replace teeth

b. Odontoceti → have teeth

2. Mysticeti (baleen and filter-feeding whales)

a. Family Balaenidae (bowhead and right whales) → 2 genera, 4 species

b. Family Balaenopteridae (rorquals: tube-throated) → 2 genera, 7 species

c. Family Eschrichtiidae (gray whale) → monotypic; Eschrichtius robustus

d. Family Neobalaenidae (pygmy right whale) → monotypic; Caperea marginata

3. Odontoceti (toothed whales) → phylogeny in debate

a. Family Delphinidae (dolphins) → 17 genera, 34 species (beaklike snout)

b. Family Phocoenidae (porpoises) → 3 genera, 6 species (blunt snout; less

streamlined)

c. Family Platanistidae (long-snouted river dolphins) → 1 genera, 2 species

d. Family Iniidae → 3 genus, 3 species

d. Family Monodontidae (narwhal and beluga) → 2 genera, 2 species

1) Narwhal (Monodon monoceros) → long, straight tusk

2) Beluga (Delphinapterus leucas) → all white

e. Family Physeteridae (sperm whales) → 2 genera, 3 species

f. Family Ziphiidae (beaked whales) → 6 genera, 21 species

III. Morphology → reflects aquatic existence

A. Streamlined body shape

1. Nearly hairless

2. Fusiform → cigar shaped

3. Insulated by thick blubber

4. Lacks sebaceous glands

5. Swimming ability → fast swimmers

a. Dorsoventral movements of tail provide propulsion

b. Flippers → steering

c. Examples

1) Dolphins → up to 36 kph (22 mph)

2) Killer whales → 55 kph (34 mph)

d. Speed most likely not due to increased power of muscles

e. Most likely due to specializations to reduce resistance (drag)

1) Laminar flow → smooth flow parallel to surface; less drag

2) Turbulent flow → water movement not parallel

3) Factors that contribute to reducing resistance

a) Hairless body

b) No obstructions → except limbs

B. Skeleton

1. Most vertebrae → high neural spines

2. Cervical vertebrae highly compressed

3. Clavicle is absent

4. Forelimbs are paddle shaped (flippers) → no external digits

a. Little movement in parts distal to shoulder

b. Proximal segments are short

c. Digits unusually long → development of more phalanges per digit

d. Used for steering

5. Hindlimbs vestigial

a. Not attached to axial skeleton

b. Not visible externally

c. Flukes → tail fins oriented horizontally; manipulated by caudal vertebrae

6. Skull → highly modified as result of posterior migration of external nares

a. Premaxillary and maxillary bones → most of the roof of the skull

b. Occipitals form the back

c. Nasals and parietal

1) Telescoped between Occipitals and Premaxillary

2) Form only a minor part of skull roof

d. Large frontals → mostly covered Premax. and max. bones

C. Adaptations for thermoregulation

1. Large body size → favorable surface area to volume ratio

2. Blubber

3. Well-developed retia mirabilia → systems of countercurrent capillaries

a. Throughout body → mainly in flippers, flukes, and head

b. Temperature regulation

D. Pair of mammae → flat along abdomen; teats enclosed within slits along the urogenital opening

E. Males → testes remain abdominal; penis is retractile

F. Breath atmospheric air

1. Alternate between periods of eupnea (normal breathing) and long periods of

apnea (cessation of breathing) → some remain submerged for over 70 minutes

2. Rapid gas exchange → enhanced by two layers of capillaries in interalveolar

septa

3. Expiration → most of air can be exhausted from lungs; humans 20% remaining

4. 12% of inhaled O₂ used; 4% in terrestrial mammals

5. 2x as many erythrocytes per volume of blood as terrestrial mammals

6. 2x to 9x as much myoglobin → molecule that stores O₂ and release to tissue

7. Vascular specializations allow blood to bypass certain muscle masses and

continue to brain

V. Natural History

A. Mysticetes

1. Named for most characteristic feature → baleen

a. Composed of keratin → protein found in epidermal tissues

b. Plates of baleen hang in comblike fashion from upper jaw only

c. Inner edge has filaments that overlap anterior plate forming a strainer

d. Grows throughout the life of the whale → inner portion worn away

e. Fetal whales have vestigial teeth → eventually lost

2. Heavily hunted → decimated their populations

3. Filter feeders

a. Feed primarily on zooplankton → from krill to fish

b. Not active predators → food passively floats in water column

c. Three distinct feeding styles

1) “Skimming” → right whales

a. Large-headed whales with conspicuous lips and long baleen plates

b. Small plankton that concentrate near surface → copepods usually

less than 1 cm

c. Swim slowly through concentrations → water and food flow into

mouth

d. As water leaves through baleen, plankton is trapped

2) “Gulping” → rorquals

a. Huge mouths and heads with short baleen

b. Extensive furrowing (tube-throat) of blubber in the throat →

forms a pouch that is distensible

c. Engulf food occurring in dense swarms → krill or fish

d. Pouch is contracted → water forced out; food trapped

3) “Scooping” → gray whale

a. Scoops material from sea floor

b. Filters out bottom-dwelling organisms

4. All greater than 7 m long → blue whale up to 27 m

5. Communicate through a variety of moans and thumps

6. Family Balaenidae

a. Distribution: most waters except tropical and south polar seas

b. Two genera and three species

1) Bowhead whale (Balaena mysticetus)

2) North Atlantic right whale (Eubalaena glacialis)

3) Southern right whale (Eubalaena australis)

4) North pacific right whale (Eubalaena japonica); newly recognized

c. Reach up to 18 m (54 ft) length; up to 100,000 kg weight

d. Heads huge → nearly 1/3 total length of body

e. Highly arched rostrum → massive lower lip

f. Lack throat grooves seen in other mysticetes

g. Dorsal fin lacking

Callosities (excrescences) occur on head of Eubalaena

7. Family Balaenopteridae (rorquals: tube-throated)

a. Distribution: all oceans

b. Size range: 8 m and 10,000 kg (minke) to 27 m and up to 200,000 kg (Blue)

c. Presence of deep longitudinal grooves in the skin, running over the entire throat

and chest

d. Long and slender bodies

e. Short pectoral fins → humpbacks have very long

f. Dorsal fins posterior to midpoint of body slender pectoral fins

g. Migrate

1) Feed in cold currents at high latitudes during summer

2) Breed at more southerly locales

h. Feed on zooplankton and small fish → larger species feed almost exclusively on

krill

8. Family Eschrichtiidae (gray whale): monotypic→ Eschrichtius robustus

a. Distribution: North Pacific coasts; Atlantic populations are extinct

b. 13−14m in size and 30,000 kg in weight

c. Slender gray body w/o dorsal fin → crenulations = series of humps along

posterior 1/3 of body

d. Flippers are broad

e. Two to five short throat grooves

f. Feed by swimming on their sides along the bottom

g. Migrate up to 18,000 km → one of the longest in mammals

h. Occur in small groups during migration

9. Family Neobalaenidae (pygmy right whale): Monotypic → Caperea marginata

a. Formerly in Balaenidae

b. Distribution: waters of Southern Hemisphere

c. Smallest of the mysticetes → 6 m in length

d. Small falcate (curves toward tail) dorsal fin

e. Highly arched rostrum like right whales

f. Has only two shallow throat grooves

g. One of the least known cetaceans

B. Odontocetes

1. Active predators → homodont dentition

2. Generally smaller than baleen whales

3.. Larger and more diverse group → 7 families, 71 species

4. Sexually dimorphic → Males larger than females

5 Known for their ability to echolocate

a. Emit variety of sounds broadly grouped into two types of sounds

b. Evidence suggests sounds produced in complex nasal sacs

c. Sound is reflected by skull; focused through oil-filled “melon”

d. Can travel greater distances than in bats

e. Echoes are received through the small mandible

f. Auditory bullae not fused with skull

1) Surrounded by

a) Connective tissue

b) System of sinuses filled with mucous emulsion

2) Allows for determining direction of signals

6. Primitive cetaceans had laterally compressed, serrated teeth → Functioned to allow

water to escape but trap small prey

7. Odontocetes radiated → replaced teeth with homodont conical teeth on slender jaws

8. Typically more social than Mysticetes

9. Family Delphinidae (dolphins)

a. Includes dolphins, killer whales, pilot whales, etc.

b. Distribution: All oceans and some rivers

c. largest family → 17 genera and 34 species

d. Small to medium cetaceans → 1.5 m and 50 kg to 10 m and 7000 kg

e. Shape of head distinctive for many

1) Forehead appears to bulge over beak-like rostrum

2) Presence of lens-shaped fatty region → melon

f. Sleek, streamlined bodies with falcate dorsal fins

g. Considerable variation in color patterns

h. Active predators → fish and squid

i. Some members highly social and live in large groups

j. Highly intelligent

k. Many species poorly known

10. Family Phocoenidae (porpoises)

a. Differences from delphinids

1) Lack a well-formed beak

2) Have a squarish head

3) Relatively robust body

b. 3 Genera & 6 species

c. Coastal waters of all oceans and connected seas of Northern Hemisphere

d. 1.5 to 2m in length; up to 120 kg in weight

e. Flippers narrow and pointed

f. Feed on a variety of fish and invertebrates

11. Family Monodontidae (narwhal and beluga)

a. Two species

1) Delphinapterus leucas (beluga)

2) Monodon monoceros (narwhal)

b. Distribution: High latitudes in arctic seas

c. Medium-sized whales → 4–6 m in length; up to 1600 kg

d. Lack dorsal fin

e. Possess melon → used for echolocation

f. Generally found in pods → up to 100 individuals

g. Migrate as a response to shifting ice pack

h. Feed mainly on the bottom → fish and invertebrates

i. Both species highly vocal

12. Family Physeteridae (sperm whales)

a. Distribution: All oceans but Arctic

b. Two genera and three species

1) Physeter catodon (sperm whale)

2) Kogia breviceps (pygmy sperm whale)

3) Kogia sima (dwarf sperm whale)

c. Sperm whale

1) Lengths of over 18 m; weigths in excess of 53,000 kg

2) Enormous head → 35% of body length

3) Feed mainly on squid; does take sharks and other fish

4) Known for incredible dives → up to 1000m and as long as 80 minutes

5) Females and young form schools; males only join during breeding season

13. Family Platanistidae

a. Taxonomic relationships have been problematic

b. All river dolphins in this family at one time

c. Currently 1 genus and two species

1) Ganges river dolphin (Platanista gangetica)

2) Indus river dolphin (Platanista minor)

d. Small cetaceans → 2-3 m long

e. Found in estuaries and rivers in India, Pakistan, & Bangladesh

f. Long beaks and small eyes which lack lens (blind)

g. Locate prey via echolocation

h. Highly endangered and not a lot known about them

14. Iniidae

a. Three genera each with one species

1) S. A. river dolphin (Inia geoffrensis) → Amazon and Orinoco rivers

2) Chinese river dolphin (Lipotes vexillifer) → Yangtze river

3) La Plata river dolphin (Pontoporia blainvillei) → coastal waters of

Argentina & S. Brazil

b. All use echolocation to find prey

c. Not a lot known about any of them

15. Family Ziphiidae (beaked whales) → Occupy all oceans

a. Six genera with 21 species → second largest family of cetacean

b. Occupy all oceans

c. Distinctive long, narrow beaks

d. Medium-sized whales → up to 13 m and 11,500 kg

e. Flippers are relatively small and oval

f. Small, falcate dorsal fin → well beyond midpoint

g. Six short throat grooves, which converge anteriorly to form a “V” pattern

h. Coloration varies from uniform brown to gray to some contrasting white

markings

i. Feed on variety of squid and fish

j. Most have 1-2 teeth in each side of lower jaw → usually only in males used for

intraspecific fighting

k. Very poorly known