Transition between land and water Flashcards
What tetrapods went back to the sea (4)
- body plan + levels of aquatic
different body plans - morphology
different levels of aquatic - fully aquatic to semi aquatic
- orca = all time under water
- penguin = only in water to hunt
- sea turtles = only go to beach to lay eggs, males do not go to the beach
number of times tetrapods went from land to sea?
27
Why such frequent returns to the sea?
- mass extinction - creates many opportunities - ecological niches - often after extinction, there is diversification event or specialisation event
- tectonic restructuring of ocean systems
- climatic changes - during warming, more opportunities = tetrapods move to sea ; melting sea ice = more ocean = more aquatic space to be used
Modern aquatic tetrapods
- how did they go back to the water?
- developed adaptations = secondary adaptations - e.g. fins and tails
- primary adaptations to live on land
- secondary adaptations = to live in the sea again (moving back to the sea)
Secondary adaptations to aquatic life
- sea turtle
- sea snake
- penguin
sea turtle - flippers and flattened body
sea snake - paddle-like tail and permeable skin
penguin - smoother surface, streamlined body
What conditions mean that terrestrial animals would need adaptations to move back to water (aquatic)?
- water creates more drag than air
- animals need to move in the water
= The aquatic problem
The aquatic problem
Moving in water
- resistance
- 2D vs 3D
- Density and viscosity
- Buoyancy
- Pressure
The aquatic problem
Moving in water - 1. resistance - appendicular vs axial swimmer
Fipper: appendicular swimmer
- only flippers move
- e.g. Plesiosaur (200 Ma), sea turlte
Fluke: axial swimmer (tail and neck)
- e.g. Mosasaur, whale
- caringiform - propulsion from start of the tail
- anguiliform - propulsion originates in the neck
increase sa - for propulsion
The aquatic problem
Moving in water - 2. from 2D to 3D
fin and smooth back = maintain stability
The aquatic problem
Moving in water - 3. water density + viscosity
- as body moves, disturbs water molecules forcing water to flow around
- water enters empty space creating turbulence and creating a sucking down force
- density -> drag created - Streamlined (dolphin): minimum water disturbance
- viscosity -> resistance of flow and more friction: slowing animals down -> smooth surface (dolphin)
ALSO - water support body - biggest animals in world = humpback whale - instead of weight on feet like in terrestrial elephants
The aquatic problem
Moving in water - 5. Water pressure
1 atmosphere (atm) for each 10 m of water depth
- blue whale fills and expands lungs on surface before diving -> during descent, lower lung collapses as body compresses from water pressure -> upper lungs are supported by cartilage which maintains its shape for ascent
- flexible ribs, collapsed lungs
The aquatic problem
Breathing (air)
-crocodiles - tolerate high levels of lactic acid
whales:
- rapid breaths (empty and refill lungs in seconds)
- efficient O2 exchange (90% vs 20% in humans)
- O2 storage in blood instead of lungs to maintain muscle activity
- slow heart rate fro diving
- blood flow to non-essential areas reduced
secondary adaptations - migration of nares on back of skull
The aquatic problem
Salt water
- drink water and excrete salt -> cells shrink -> dehydration
- sea turtles excretion of salt through salt glands through eyes
The aquatic problems
Heat conductivity
- water moves heat 24x faster than air - gets cold faster
Homeothermy
- stop heat from leaving body - thick blubber, water-repellent oil, fur, no dorsal fin
Ectotherms
- tropical distribution - crocodiles move to the tropics
The aquatic problem
Senses - Sight
sun - bends less in water, travels slower, filters cooler colours
- larger eyes - sea turtles; Ichthyosaurus = has biggest eyes out of all that have secondary adaptations -> lens enlarged and spherical -> more rod cells -> photoreceptors that allow seeing in low light levels
