@article{TEXTUAL,
      recid = {8226},
      author = {Sereno, Paul C. and Martinez, Ricardo N. and Wilson,  Jeffrey A. and Varricchio, David J. and Alcober, Oscar A.  and Larsson, Hans C. E.},
      title = {Evidence for Avian Intrathoracic Air Sacs in a New  Predatory Dinosaur from Argentina},
      journal = {PLOS ONE},
      address = {2008-09-30},
      number = {TEXTUAL},
      abstract = {&lt;p&gt;Background: Living birds possess a unique heterogeneous  pulmonary system composed of a rigid, dorsally-anchored  lung and several compliant air sacs that operate as  bellows, driving inspired air through the lung. Evidence  from the fossil record for the origin and evolution of this  system is extremely limited, because lungs do not fossilize  and because the bellow-like air sacs in living birds only  rarely penetrate (pneumatize) skeletal bone and thus leave  a record of their presence.&lt;/p&gt;&lt;p&gt;Methodology/Principal  Findings: We describe a new predatory dinosaur from Upper  Cretaceous rocks in Argentina, &lt;em&gt;Aerosteon  riocoloradensis&lt;/em&gt; gen. et sp. nov., that exhibits  extreme pneumatization of skeletal bone, including  pneumatic hollowing of the furcula and ilium. In living  birds, these two bones are pneumatized by diverticulae of  air sacs (clavicular, abdominal) that are involved in  pulmonary ventilation. We also describe several pneumatized  gastralia (“stomach ribs”), which suggest that diverticulae  of the air sac system were present in surface tissues of  the thorax.&lt;/p&gt;&lt;p&gt;Conclusions/Significance: We present a  four-phase model for the evolution of avian air sacs and  costosternal-driven lung ventilation based on the known  fossil record of theropod dinosaurs and osteological  correlates in extant birds:&lt;/p&gt;&lt;p&gt;(1) Phase I—Elaboration  of paraxial cervical air sacs in basal theropods no later  than the earliest Late Triassic.&lt;/p&gt;&lt;p&gt;(2) Phase  II—Differentiation of avian ventilatory air sacs, including  both cranial (clavicular air sac) and caudal (abdominal air  sac) divisions, in basal tetanurans during the Jurassic. A  heterogeneous respiratory tract with compliant air sacs, in  turn, suggests the presence of rigid, dorsally attached  lungs with flow-through ventilation.&lt;/p&gt;&lt;p&gt;(3) Phase  III—Evolution of a primitive costosternal pump in  maniraptoriform theropods before the close of the  Jurassic.&lt;/p&gt;&lt;p&gt;(4) Phase IV—Evolution of an advanced  costosternal pump in maniraptoran theropods before the  close of the Jurassic.&lt;/p&gt;&lt;p&gt;In addition, we  conclude:&lt;/p&gt;&lt;p&gt;(5) The advent of avian unidirectional lung  ventilation is not possible to pinpoint, as osteological  correlates have yet to be identified for uni- or  bidirectional lung ventilation.&lt;/p&gt;&lt;p&gt;(6) The origin and  evolution of avian air sacs may have been driven by one or  more of the following three factors: flow-through lung  ventilation, locomotory balance, and/or thermal  regulation.&lt;/p&gt;},
      url = {http://knowledge.uchicago.edu/record/8226},
}