1. Density 820x greater than air.
2. Dissolved Oxygen 26x less than air.
3. Thermal Conductivity is 23x greater in water.
4. Attenuation coefficient of light is greater than 300x in water.
5. Sound travels 4.6x faster in water and the attenuation coefficent is 1/10 of that in air.

• Gravitational force is greatly diminshed because marine mammals have a density about equivalent to water.
• A larger body size is possible & their is a lower cost of energy.

• Streamlined body shape influenced by increased hydrodynamic drag force during locomotion.
• Reduction or modification of external limbs (to flukes or flippers).
• Internalization of male genitalia (except during copulation).

• Molecular diffusion and convection are slower in water.
• Largely no olfactory ability in fully aquatic marine mammals.

• Hydrostatic pressure increase by 1 ATM per 10m in depth.
• Collapsible airways and pulmonary shunts (prevents decompression sickness).

• Water breathing with lungs is not possible, due to its high density.

• Nostrils/blowholes are located on top of the head and are closed during breath-holding.

• Marine mammals rely on systemic O₂ stores while diving.
• Pronounced dive response in deep diving species.
• Increased myoglobin & hemoglobin concentrations.

• Newborn animals must be able to swim and nurse while breath-holding.

• Marine mammals must be well insulated to maintain core body temperature ~37^oC.
• Blubber is a thermal insulator with counter-current circulatory heat exchange.

• Increased activity level and Basal Metabolic Rate.

• Some marine mammals achieve a larger size (less SA:V) to reduce heat loss.

• Limited range for herbivorous marine mammals.

• Maximum penetration of light ~1,300m and the average depth of the ocean is ~3,700m; therefore, most of the ocean is dark.
• Deep-diving species either echolocate or have enlarged eyes with highest sensitivity at 540nm (blue-green region).

• Echolocation, remote-sensing, and social communication are possible.

• Low frequency sound can travel for 1,000s of miles in the ocean.

Two (2) Families of Order Odontoceti ("toothed whales") & Four (4) Families from Order Mysticeti ("baleen whales").

+Example

• Odontoceti
• Monodontidae (Beluga whale)
• Physeteridae (Sperm whale)
• Mysticeti
• Balaenidae (Bowhead whale)
• Neobalaenidae (Pygmy Right whale)
• Balaenopteridae (Rorquals)
• Eschrichtiidae (Grey Whale)

• 200+ long baleen plates
• Large, high-arched jaw
• No gular grooves
• Scim/Ram feeders

• Moderately-arched mouth.
• Intermediate between Balaenidae and Balaenopteridae.
• Speculation on their feeding strategy, though they prey on krill and copepods.

• Gulp/Lunge feeders that slowly filter it with baleen of upper jaw.
• 200+ short baleen plates.
• Many gular grooves.
• Dorsal fin.

• Slightly arched head.
• 130-180 short baleen plates.
• 2-5 gular grooves.
• Feed on invertebrates sucked up and filtered through baleen plates, from the benthos.

• Well developed, conical teeth.
• No gular grooves.
• Small subterminal jaw.
• Feed at deep depths, usually on squid/octopus.

• No gular grooves.
• 8-11 irregularly shaped teeth.
• Feed opportunistically on benthic invertebrates and fish.