Download Form to Function

Form to Function:
Body Shape and Locomotion
in the Aquatic Environment
Fish
History
• 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
Thompson 1971
Body Shape and Locomotion
• Body and Caudal Fin (BCF) locomotion
• Anguilloform
– Whole body
– Elongated, slender, flexible
bodies
• Subcarangiform/Carangiform
– 2/31/3 of body
– Stiffer body and caudal fin
• Thunniform
– Stiff body
– Only caudal fin and
attachment
– High crescent shaped caudal
fin
Sfakiotakis et al. 1999
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
• 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
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
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
•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
Bejder and Hall 2002
Ambulocetus
Thewissen and Bajpai 2001
•Evolution: streamlined body, loss of fur,
backward shift of nostrils, transformation
of forelimbs into flippers, flukes for
swimming, loss of hindlimbs
Body Shape and Locomotion
•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
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