BIOD43H3 Lecture Notes - Lecture 5: Hydrophiinae, Parasitic Drag, Turbulence
Tutorial 5:
1. The authors acknowledge that a transition from locomotion on land or in the air to
locomotion in water is associated with many morphological changes. Consider the penguin.
Identify some morphological differences between penguins and most flying birds and
consider how the physical differences between air and water may underlie these differences.
Moving rapidly through a dense medium such as water rather than through air requires
dramatic modifications of body shape, and of the ways in which propulsive forces are
delivered. Flying birds have wings with feathers that are adapted for flight, while penguins
have tapered, flattened flippers that push against the water. These flippers allow penguins to
move underwater with the speed of a flying bird. The general body shape of a penguin is
streamlined for swimming in contrast to flying birds.
Answer:
• Penguins have denser, thicker bones that can help them overcome buoyancy for diving
• Penguins can change their volume in lungs, negative pressure acting against buoyancy,
lighter so that they can float
• Flying birds have an increased area in wings. Penguins have very small feathers
• Penguin flippers are quite small relative to body size
o But they generate enough lift to swim
o Difference in density between air and water and how these structures are
efficient in respective environments
• Flippers are a lot more dense/solid, water being more viscous/dense than water, would
need denser flippers to withstand this density
• Drag is very small compared to lift in penguin flippers
• Streamlined design helps reduce pressure drag, discouraging turbulent flow
• Hydrofoil with increased pressure on bottom of fin to generate lift
• Big feathers create more drag in water, but not in air
2. At the top of page 318 the authors talk aout hat gradualist theories of adaptatio
would suggest about the initial evolution of a small paddle. What reasons do the authors
idetify for hy a sall paddle ay hae, i the iitial stages after its eolutio, ee ore
effetie ? Ca you relate this idea to the morphological differences you identified between
penguins and other birds?
In the initial stages of adaptation, a small paddle may be more effective than a larger paddle
because the muscular strength and skeletal supports needed to overcome the water resistance
of a large paddle would develop only later in the adaptive shift from land to the oceans.
Answer:
• More efficient to have small tail because of the cost needed to generate
musculoskeletal structures to support a bigger tail.
• Penguins developed small flippers as opposed to large ones for fast underwater
movement when they were in water and this would be a gradual change.
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Document Summary
Tutorial 5: the authors acknowledge that a transition from locomotion on land or in the air to locomotion in water is associated with many morphological changes. Identify some morphological differences between penguins and most flying birds and consider how the physical differences between air and water may underlie these differences. Moving rapidly through a dense medium such as water rather than through air requires dramatic modifications of body shape, and of the ways in which propulsive forces are delivered. Flying birds have wings with feathers that are adapted for flight, while penguins have tapered, flattened flippers that push against the water. These flippers allow penguins to move underwater with the speed of a flying bird. The general body shape of a penguin is streamlined for swimming in contrast to flying birds. Tigersnakes are abundant in riparian habitats and frequently enter the water to forage or to escape from predators. Authors need to look at evolutionary function of flattened tail.
