Week 9: Birds

• ICTHYOPTERYGIA


  • Early Triassic to early Late Cretaceous
  • Dominant marine predator in Mesozoic oceans
  • Largest: over 20m
  • Array of dentition in fossil records
  • Further support of its wide-spreading dominance and diversity

  
• ICTHYOPTERYGIA


  • Evidence of live births
  • Origin of live births
  • Fossil with calf in birthing placement
  • Some reached sperm whale size
  • Shonisaurus sikanniensis (21 m)

  
• ICTHYOPTERYGIA

  • Evidence of the bends
  • Bone damage found in fossil bones
  • Weakened bone from nitrogen bubbles forming inside bone
  • Surfaced too quickly to evade predator (sharks, crocodiles)
• SAUROPTERYGIA


  • Another diapsid specialized for aquatic lifestyle
  • Emerged Triassic Period
  • Long, flat skull
  • Long, flexible neck (80 vertebrae)
  • Early forms had shorter necks

  
• Neck elongation appeared independently across tetrapod groups


  • Pterosaurs (air)
  • Sauropod (and giraffes)
  • Mesosaurs
  • Icthyopterygia
  • Sauropterygia
  • Others?
  • Amphibians?

  
• EUREPTILIAN RADIATION (Diapsida)


  • Archosauromorpha
  • Euryapsida
  • Lepidosauromorpha
  • Testudinata
• LEPIDOSAURIA


  • Modern snakes, lizards (and ancestors): 4000+ extant species
  • Order Eosuchia (extinct): ancestor all modern snakes, lizards
  • Order Squamates: snakes, lizards and tropical/subtropical reptiles
  • Largest living scaled reptile

  
• LEPIDOSAURIA


  • Modern skull
  • Modified diapsid
  • Loss of lower temporal fenestrae
  • Fused teeth to skull

  
• LEPIDOSAURIA

  • Gekkota
  • Serpenta

  
• LEPIDOSAURIA

  • Long and generally slender hind limbs
  • Reduced or absent limbs (snakes, ancestors hunted in borrows = easy access without limbs was beneficial)
• Snake: hyperkinetic skull


  • 20 skull bones
  • Articulated but not fused
  • Connect through muscle
  • Can independently move bones
  • Open jaw wide
  • Does not dislocate jaw
  • Along with lack of limbs, allows feeding of animals much larger than themselves
• TESTUDINATA

  • First appeared in late Triassic
  • Skull dilemma: anapsid
  • Suggests early placement in reptilian lineage
  • Evidence suggests they are derived diapsid
  • Closed hole later on
• TESTUDINATA


  • Abrupt redesign of amniote body plan: shell
  • Dorsal carapace
  • Expanded ribs and surface skin plates
  • Connected ventral plastron of fused bony pieces
• • Turtle ancestor: Eunotosaurus africanus
  • 260 MYA (30 MY before dinsaorus)
  • Earliest-known turtle with fully formed shell: 210 MYA

  
• Turtles have been missing their Archaeopteryx
• TURTLE SHELL EVOLUTION


  • Flattening and expansion of rib
  • Pappochelys: Belly protected by rod-like bones, some fused together: plastron
  • Development in aquatic environment to protect from predator ambush from below
  • Two openings behind eye socket
  • Turtles derived from diapsid
  • Proganochely: Carapace (back portion of shell) appears later in fossil record, closely resembles modern turtles

  
• MODERN TESTUDINATA


  • Suborder Cryptodira (hidden-necked): Vertical retraction, Sea Turtle
  • Suborder Pleurodira (side-necked): Horizontal retraction, African sideneck turtle
• Within Dinosauria (clade) we have: Aves

  
• Aves are "Glorified reptiles"
• DINOSAURIA TO AVES

  • Radiated from dinosaurs
  • Order Saurischians
  • Subgroup Theropods

  
• COELUROSAURS


  • Subgroup of Theropod
  • Some had feathers
  • Early feathers: elaborate reptilian scales
• Archeopteryx was the key fossil for the transition from non-avian Dinosaurs to birds

  
• ARCHEOPTERYX


  • First discovered in the 1800s
  • Some later fossils mistaken for pterosaurs
  • Feathered dinosaurs
  • Share avian features and reptilian features

  
• ARCHEOPTERYX


  • Jawed Teeth
  • Clawed Fingers
  • Keel-less sternum (REPTILIAN)
  • Forelimbs and girdle = wings
  • Furcula (wishbone)
  • Feathers (AVIAN)

  
• FEATHER MORPHOLOGY


  • Feathers evolved before birds, from reptilian scales
  • Maybe 175 MYA
  • Even at 150 MYA, it is no doubt a feather
  • Laid along distinctive tracts: pterylae
  • Apterylae: areas without feathers
  • Feather structures differ
• FEATHER MORPHOLOGY

  • Tubular central shaft: rachis
  • Either side of rachis: vane
  • Rachis + vane = spathe
  • Connected to shaft: series of barbs
  • Interlocking connections in bars: barbules
  • Feather anchored to body: calamus (quill)
• REPTILIAN


  • Forelimbs and girdle = wings
  • Furcula (wishbone)
  • Feathers
• AVIAN


  • Coracoid: prevents wings crushing thorax on downstroke
  • Furcula: strengthens skeleton for flight
• ARCHEOPTERYX


  • Jawed Teeth
  • Clawed Fingers
  • Keel-less sternum

  
• ARCHEOPTERYX

  • Forelimbs and girdle = wings
  • Furcula (wishbone)
  • Feathers ('angel fossil')
• Feathers evolved before birds, from reptilian scales
• Feather evolution maybe 175 MYA
• Pterylae


  Areas with feathers
• Apterylae


  Areas without feathers
• Feather morphology


  • Tubular central shaft: rachis
  • Either side of rachis: vane
  • Rachis + vane = spathe
  • Connected to shaft: series of barbs
  • Interlocking connections in bars: barbules
  • Feather anchored to body: calamus (quill)
• Feathers for flight

  • Well-defined central shaft
  • Long, asymmetrical vanes about rachis
• Feathers for insulation/ornamentation

  • Poorly defined rachis
  • More flexible structure
  • Symmetrical vanes about rachis
• Archeopteryx not the only feathered dinosaur
• Feather types found across Theropod subgroups


  • Downlike
  • Symmetrical
  • Flight
• ANCHIORNIS


  • 160 MYA: Pre-Archeopteryx
  • Chicken-sized
  • Flight feathers on forearms
  • Fuzzy coating over body
  • Long feathers on hindlegs