Form to Function: Body Shape and

Locomotion in the Aquatic Environment

Fish

History

Thompson 1971

• 550 million years ago• >25 950 species today• “Natural selection has

ensured that the mechanical systems [that] evolved in fish…are highly efficient with regard to the habitat and mode of life for each species.” (Sfakiotakis et al. 1999, 237)

• Began as jawless anguilloform parasites

• Now have a variety of forms

Body Shape and Locomotion

Sfakiotakis et al. 1999

• Anguilloform– Whole body– Elongated, slender,

flexible bodies

• Subcarangiform/Carangiform– 2/31/3 of body– Stiffer body and caudal fin

• Thunniform– Stiff body – Only caudal fin and

attachment– High crescent shaped

caudal fin

• Body and Caudal Fin (BCF) locomotion

Ecology, Tradeoffs, and Conservation

• Found in every existing aquatic habitat

• Many species endangered because of fishing pressures

• Habitat destruction• Pollution

• Speed comes at the cost of maneuverability

• Have other types of locomotion for foraging and maneuvering

Sea Turtles

History• Family Cheloniidae• 90 million years ago• Evolved from

amphibious form• Order testudinomorpha

is a sister taxon to crocodilia

•Ancestral forms were sequential quadrupedal paddlers

–Hindlimbs larger than forelimbs

•Modern forms “fly”-synchronous pectoral gait

–Forelimbs are much larger than hindlimbs

Body Shape and Locomotion

Davenport et al. 1984

• Clawless, smooth, long, flat feet

• Short blunt head and neck

• Non-retractable head and limbs

• Smooth flexible shell• Tear drop shaped

– Rounded blunt front with gently tapered rear with flat bottomed hydrofoil shape

• one of the fastest moving reptiles

• Hypertrophied forelimbs generate thrust on upstroke and downstroke

• Lift based movement much like flying

• Hindlimbs are used as rudders/elevators

Ecology, Tradeoffs, and Conservation

• Habitat/Nesting site destruction/degradation

• Pet trade • Caught in fishing nets• Low reproductive rates• Are unable to protect

young

• Faster swimmers• Efficient • Pelagic• Nearly invulnerable

to predation as adults

• Poor terrestrial– Movement– Nests

• Diet– Jellyfish, eelgrass

PENGUINS(Spheniscidae)

History

• Tertiary period (60 million years ago)

•Evolved from flying birds similar to albatrosses

•Earliest fossils from New Zealand

•Forelimbs shorter/broader than modern albatross’, not as short/broad as modern penguins’

•Semi-flexible elbows

•Places where muscle attached to bone suggests foot-propulsion

•Phylogeny disputed

Body Shape and Locomotion

•Streamlined body

•Feathers

•Stiff – reduces vibration and fluttering

•Tightly packed (up to 70 per square inch)

•Oil gland near tail

•Bones

•Thick and dense

•Wing-propelled

•Flipper-shaped wings used in flying motion

•Allows thrust on upstroke and downstroke

Ecology, Trade-offs, and Conservation

•17 modern species

•Spend up to 75% of life in water

•Inhabit islands and remote parts of continents in Southern Hemisphere

•Cannot fly to escape predators

•Short legs make for inefficient walking on land (waddling)

•Tobagganing

•All species protected under law, 3 considered at risk

•Threats include hunting, habitat destruction, global warming

•Non-native predators

•Cannot fly to escape dogs

•Oil pollution

•Have to surface to breathe

CETACEANS (Whales, Dolphins,

and Porpoises)

History

Ambulocetus

•Eocene (40-50 million years ago)

•Terrestrial quadrupedal ancestor from extinct suborder Archaeoceti

•Pakicetus Ambulocetus Rodhocetus Basilosauridae Durodontidae

•Quadrupedal paddling pelvic paddling dorsoventral undulation caudal oscillation

•Evolution: streamlined body, loss of fur, backward shift of nostrils, transformation of forelimbs into flippers, flukes for swimming, loss of hindlimbs

Bejder and Hall 2002

Thewissen and Bajpai 2001

•Body shape for decreased drag

•Streamlined shape

•Loss of hindlimbs

• Thunniform swimming – caudal oscillation

•Resembles a standing wave

•Lower third of body and caudal fluke moved through water in vertical plane

•Specialized caudal fluke – lunate shape, provides thrust on both upstroke and downstroke

•Vertebral column – controls movement, dampens oscillations, acts as shock absorber

Body Shape and Locomotion

Ecology, Trade-offs, and Conservation•76 extant species

•Inhabit every ocean of the world

•Size range from 4 feet and 100 pounds (dolphin) to 100 feet and 130 tons (blue whale)

•Disadvantage: they are large animals, one or two large young at a time that require parental care. This makes population growth slow.

•Many species are endangered

•Threats: commercial whaling, entanglement in fishing gear, collisions with ships, marine pollution

Conclusions

• more efficient methods of swimming – drag based paddling lift based oscillation

• Reducing drag– Streamlining shape– Eliminating extra limbs/claws/hair

• Variety of forms developing at different times from separate beginnings