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Majungatholus with Avian Air Sacs



  O'Connor, P. M. and L. P. A. M. Claessens. 2005. Basic pulmonary design and
    flow-through ventilation in non-avian theropod dinosaurs. _Nature_
    436:253-256.

Abstract:
  "Birds are unique among living vertebrates in possessing pneumaticity of the
   postcranial skeleton, with invasion of bone by the pulmonary air-sac system.
   The avian respiratory system includes high-compliance air sacs that
ventilate
   a dorsally fixed, non-expanding parabronchial lung. Caudally positioned
   abdominal and thoracic air sacs are critical components of the avian
   aspiration pump, facilitating flow-through ventilation of the lung and
   near-constant airflow during both inspiration and expiration, highlighting a
   design optimized for efficient gas exchange. Postcranial skeletal
   pneumaticity has also been reported in numerous extinct archosaurs including
   non-avian theropod dinosaurs and *Archaeopteryx*. However, the relationship
   between osseous pneumaticity and the evolution of the avian respiratory
   apparatus has long remained ambiguous. Here we report, on the basis of a
   comparative analysis of region-specific pneumaticity with extant birds,
   evidence for cervical and abdominal air-sac systems in non-avian theropods,
   along with thoracic skeletal prerequisites of an avian-style aspiration
pump.
   The early acquisition of this system among theropods is demonstrated by
   examination of an exceptional new specimen of *Majungatholus atopus*,
   documenting these features in a taxon only distantly related to birds. Taken
   together, these specializations imply the existence of the basic avian
   pulmonary Bauplan in basal neotheropods, indicating that flow-through
   ventilation of the lung is not restricted to birds but is probably a general
   theropod characteristic."

  Cheers,

Jaime A. Headden

"Innocent, unbiased observation is a myth." --- P.B. Medawar (1969)


                
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