BIOL2712 Study Guide - Final Guide: Malleefowl, Thecodontia, Hoatzin
25 Jun 2018
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Birds
Very diverse and successful group that evolved during the great reptile radiation of
the Mesozoic
Reptilian vestiges are found in birds:
oAmniotic eggs
oScales
Characteristics of Birds
Virtually their whole anatomy is adapted to flight
Reduction of some organs
oE.g. only 1 ovary
Bones are honeycombed
oLight but strong
oPigeon skull is 0.21% of body weight
Rat = 1.25% i.e. 6x heavier
oSkeleton of a Frigatebird (2m wingspan)
Weighs 113 grams (less than feathers)
Replace heavy jaws and teeth
oFood can be chewed in muscular gizzard
Crocodiles have gizzards, as did some dinosaurs
Keratinized bill is light and strong and adapted into a huge range of shapes for
specialized diet
Efficient circulatory system
o4-chabebered heart
Highly efficient respiratory system
oOne-way flow of air instead of the tidal system in other tetrapods
Air sacs dissipate heat and reduce density
Brains are proportionally larger than amphibians and reptiles
oMore complex behaviour
Acute eyesight
oBest in vertebrates
Sense of smell poor
oExcept in a few species
E.g. turkey vulture
Excellent coordination for safe flight
Flight
The wings of most birds are aerofoils
oStructure with curved surfaces to give the most favourable ratio of lift to drag
The wings are powered by large pectoral muscles attached to keel of modified
sternum
find more resources at oneclass.com
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oBreastbone
Wing Shapes Are Adapted to
Different Types of Flight
Soaring
oEagles and vultures
Stooping
oPeregrine falcon
(300km/h)
Rapid hawing
oSwallows
Constant flight
oAlbatrosses
oSwifts (sleep and copulate in flight)
Hovering
oHumming birds – very rapid wing beats
Amniotic Egg
Amniotic egg is shelled, hence internal fertilization
oOften with awkward copulation as most birds lack a penis
Eggs incubated by female, male or both
Note: mound builders
oE.g. Malleefowl – use heat of rotting vegetation
Feathers
Diagnostic
Made of keratin and have the following features
oLight and strong
oReplaceable
Plus, moult at least every 2 years
oGood insulation in cold and heat
oManipulable for fine control in flight
Evolution of Flight
Pterosaurs were flying before birds and some coexisted with the earliest birds
oInsects – 350 mya
oPterosaurs – 200 mya
oBirds – 140 mya
Lacked the fine flight control that is characteristic of birds
oCarried a heavy skeleton including a set of jaws and heavy teeth
Some of the later Prersaurs (such as Pteranodon – wingspan 8m)
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
Very diverse and successful group that evolved during the great reptile radiation of the mesozoic. Reptilian vestiges are found in birds: amniotic eggs, scales. Virtually their whole anatomy is adapted to flight. Reduction of some organs: e. g. only 1 ovary. Bones are honeycombed: light but strong, pigeon skull is 0. 21% of body weight. Rat = 1. 25% i. e. 6x heavier: skeleton of a frigatebird (2m wingspan) Replace heavy jaws and teeth: food can be chewed in muscular gizzard. Crocodiles have gizzards, as did some dinosaurs. Keratinized bill is light and strong and adapted into a huge range of shapes for specialized diet. Highly efficient respiratory system: one-way flow of air instead of the tidal system in other tetrapods. Brains are proportionally larger than amphibians and reptiles: more complex behaviour. Sense of smell poor: except in a few species. The wings of most birds are aerofoils: structure with curved surfaces to give the most favourable ratio of lift to drag.
