Phylogeny%20of%20Birds%20

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Phylogeny of Birds Class Aves

• Birds first appear, unambiguously, in the fossil
  record in the Jurassic (150 mya). First bird is
  Archaeopteryx.
• Transitional form between reptiles and modern
  birds.
• Possessed reptilian skull with teeth, long bony
  tail, and claws on digits, but had feathers just
  like modern birds.

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Archaeopteryx
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Origin of Birds

• Two schools of thought on bird ancestry
• Coelurosaurian Theropod (Dinosaur) Ancestry
  contends that birds derived from dinosaurs
  because they share many unique skeletal
  characteristics.
• Main problem coelurosaurs are contemporaneous
  or later than early birds and you cant be older
  than your ancestors. But, coelurosaurs and birds
  may share common ancestor.
• Thecodont Ancestry contends that birds are
  derived from thecodont ancestor, probably in late
  Triassic period.
• Main problem thecodonts are primitive
  archosaurs and not many unique skeletal features
  are shared between them and Archaeopteryx.

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Thecodont
Coelurosaur
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Fig 3.27 Phylogenetic relationships among the
Amniotes
Note that birds are included within the
dinosaurs in this phylogeny
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Archaeopteryx and Bird Origins

• Archaeopteryx was capable of powered flight
• Shows features of modern flying birds (asymmetric
  feather vanes, acute scapula-coracoid angle),
  although flight apparatus was primitive.
• So, because early birds flew, all subsequent
  birds were derived from flying ancestors.
• Because of adaptations for flight, birds are
  anatomically very uniform, moreso than any other
  vertebrate Class.

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Angle in flightless birds
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Classification of Birds

• Class Aves divided into 2 Subclasses
• Subclass Sauriurae
• Infraclass Archaeornithes Archaeopteryx
• Infraclass Enantiornithes opposite birds
  adaptive radiation in Cretaceous, but extinct by
  end of Cretaceous
• Subclass Ornithurae
• Infraclass Odontornithes Cretaceous toothed
  birds, extinct at end of Cretaceous.
• Infraclass Neornithes
• Superoder Paleognathae ratites and tinamous
• Superorder Neognathae includes most modern
  birds
• Approximately 30 Orders of living birds and
  10,000 species.

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Avian Phylogeny based on Feduccia (1995, 2003)
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Enantiornithes
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Icthyornis
Hesperornis
Odontornithes
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Rhea South America
Ostrich - Africa
Cassowary Australia
Emu Australia
Kiwi New Zealand
Paleognathae
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Class Mammalia

• Derived from Therapsid (Cynodont) ancestors in
  Triassic (200 mya).
• Early forms very similar in appearance to some
  Therapsids fossil mammals distinguished by
  squamosal-dentary jaw joint (quadrate-articular
  joint in therapsids and reptiles)
• First mammals likely small and nocturnal
• After extinction of dinosaurs at end of
  Cretaceous, mammals became dominant land
  vertebrates.
• Endothermy and high capacity for activity (like
  birds) probably assisted in rise to dominance.

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Thrinaxodon
Cynognathus
Examples of Cynodont Therapsids These possessed
turbinates in nasal passages suggestive
of endothermy (note the hair in
these reconstructions) Cynodonts as a group were
extinct by the end of the Triassic, but gave rise
to the mammals
Oligokyphus
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Fig 3.42 Phylogenetic relationships among the
Synapsids
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Class Mammalia

• All have hair and nurse young
• Possess heterodontous teeth specialized for
  specific functions
• Other unique traits sweat and sebaceous glands,
  anucleate red blood cells
• Divided into 2 Subclasses (about 5500 total
  species)
• Subclass Monotremata includes platypus and
  spiny echidna
• Lack nipples and external ears
• Embryos develop in shelled eggs
• Subclass Theria (all bear live young and nurse
  through nipples)
• Infraclass Symmetrodonta
• Infraclass Metatheria Marsupials
• Infraclass Eutheria Placental Mammals

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Spiny Echidna
Duck-billed Platypus
Living Monotremes
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Subclass Theria

• Infraclass Symmetrodonta
• Basal group of Mesozoic Mammals (Triassic to late
  Cretaceous)
• Molars are triangular when viewed from above
• Perhaps not a monophyletic group
• Infraclass Metatheria Marsupials (1 Order)
• Young born very immature, develop in marsupium
  (pouch)
• Includes kangaroos, koalas, opossum
• Main current diversity in Australia
• Infraclass Eutheria Placental Mammals (includes
  4 Orders and 18 Suborders)

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Symmetrodonts
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Fig 3.45