Birds

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Bilogical diversity - Birds

  • subclass Vertebrata: clade Archosauria (Archosaurs+avian reptiles)
  • birds grouped - reptiles. reptilian features = modified 
  • common - diapsid skull - single occipital condyle, 1 ear bone
  • nucleated red blood cells
  • reptile like scales - legs (homologous)
  • evolution - birds - descendents, theropods
  • many had feathers - not capable - flight - sexual signalling+insulation 
  • evolution - birds
  • Deinonychus: feathered dinosaur = transitional form 
  • feathers - theropods - evidence, endothermy?
  • maintain body temperature above ambient using metabolic heating
  • animals more active hunters - higher metabolic demand - higher mitochondrial density - higher heat generated 
  • heat retained via insulation - maintain internaml temperature - enzyme activity 
  • advantages = maintenance - core internal processed - can be active - ectotherms can't+inhabit more extreme conditions
  • disadvantages = energetically expensive = limiting - food scarce. higher consumption - equivalent sized ectotherms - match metabolism
  • evolution - birds = Archaeopteryx = 145 mya oldest known bird
  • reptilian features = teeth, long tails, clawed forelimbs 
  • avian features = feathers, foot structure, paired clavicle (furcula), avian pelvic girdle
  • unlikely capable - powered flight. sternum+wrist articulation 
  • evolution - flight. hypothesis 1 = bottom up - wings - additional thrust = escaping predators/chasing prey
  • hypothesis 2 = top down - flight - climbing therapods - modified insulatory feathers glide - canopy
  • top down route - Archaeopteryx
  • 65 mya (Cretaceous) fossilised skeletons - powered flight possible
  • large, keeled sternum - Icthyornis (retained reptilian dentition - similar morphological features - modern birds)
  • clade Archosauria: class Aves
  • 55 mya = giant terrestrial flightless bird = Diatryma (2m)+Phorusrhacidae (3m)
  • both thought - carnivores but Diatryma herbivore 

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