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Evidence for avian intrathoracic air sacs in a new predatory dinosaur from Argentina.

Sereno PC, Martinez RN, Wilson JA, Varricchio DJ, Alcober OA, Larsson HC - PLoS ONE (2008)

Bottom Line: 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.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.

View Article: PubMed Central - PubMed

Affiliation: Department of Organismal Biology and Anatomy, University of Chicago, Chicago, Illinois, USA. dinosaur@uchicago.edu

ABSTRACT

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.

Methodology/principal findings: We describe a new predatory dinosaur from Upper Cretaceous rocks in Argentina, Aerosteon riocoloradensis 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.

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: (1) Phase I-Elaboration of paraxial cervical air sacs in basal theropods no later than the earliest Late Triassic. (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. (3) Phase III-Evolution of a primitive costosternal pump in maniraptoriform theropods before the close of the Jurassic. (4) Phase IV-Evolution of an advanced costosternal pump in maniraptoran theropods before the close of the Jurassic. In addition, we conclude: (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. (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.

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Cladogram of Dinosauria showing the four-phase model for evolution of avian air sacs and lung ventilation within Theropoda.Phase I (Theropoda), variable posterior extension of paraxial cervical air sacs. Phase II (Tetanurae), elaboration of cranial (clavicular) and caudal (abdominal) intrathoracic air sac divisions and subcutaneous diverticulae. Phase III (Maniraptoriformes), primitive costosternal ventilatory pump. Phase IV (Maniraptora), advanced costosternal ventilatory pump. Abbreviations: aas, abdominal air sac; cas, cervical air sac; caas, caudal air sacs; clas, clavicular air sac; cor, coracoid; cras, cranial air sacs; lu, lung; sr, sternal rib; st, sternum; up, uncinate process; vr, vertebral rib. Bold arrow on lung indicates flow-through lung ventilation; question mark indicates uncertainty in the direction of air flow (uni- or bidirectional).
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pone-0003303-g017: Cladogram of Dinosauria showing the four-phase model for evolution of avian air sacs and lung ventilation within Theropoda.Phase I (Theropoda), variable posterior extension of paraxial cervical air sacs. Phase II (Tetanurae), elaboration of cranial (clavicular) and caudal (abdominal) intrathoracic air sac divisions and subcutaneous diverticulae. Phase III (Maniraptoriformes), primitive costosternal ventilatory pump. Phase IV (Maniraptora), advanced costosternal ventilatory pump. Abbreviations: aas, abdominal air sac; cas, cervical air sac; caas, caudal air sacs; clas, clavicular air sac; cor, coracoid; cras, cranial air sacs; lu, lung; sr, sternal rib; st, sternum; up, uncinate process; vr, vertebral rib. Bold arrow on lung indicates flow-through lung ventilation; question mark indicates uncertainty in the direction of air flow (uni- or bidirectional).

Mentions: The form of the pectoral and pelvic girdles in the holotypic skeleton clearly indicate that Aerosteon is a basal tetanuran (Figure 17). These features, which include the unexpanded crescentic coracoid, relatively broad scapular blade, relatively narrow brevis fossa and robust pubic peduncle of the ilium, and open obturator notch and large boot of the pubis, and sacrum limited to five vertebrae, closely resemble the condition in the allosauroids Allosaurus [47] and Acrocanthosaurus [49], [50], [54]. The small prefrontal and triradiate postorbital, which shows no development of a swollen brow or infraorbital flange, are closest to that in Allosaurus and very different from that in abelisaurids and carcharodontosaurids [15], [51].


Evidence for avian intrathoracic air sacs in a new predatory dinosaur from Argentina.

Sereno PC, Martinez RN, Wilson JA, Varricchio DJ, Alcober OA, Larsson HC - PLoS ONE (2008)

Cladogram of Dinosauria showing the four-phase model for evolution of avian air sacs and lung ventilation within Theropoda.Phase I (Theropoda), variable posterior extension of paraxial cervical air sacs. Phase II (Tetanurae), elaboration of cranial (clavicular) and caudal (abdominal) intrathoracic air sac divisions and subcutaneous diverticulae. Phase III (Maniraptoriformes), primitive costosternal ventilatory pump. Phase IV (Maniraptora), advanced costosternal ventilatory pump. Abbreviations: aas, abdominal air sac; cas, cervical air sac; caas, caudal air sacs; clas, clavicular air sac; cor, coracoid; cras, cranial air sacs; lu, lung; sr, sternal rib; st, sternum; up, uncinate process; vr, vertebral rib. Bold arrow on lung indicates flow-through lung ventilation; question mark indicates uncertainty in the direction of air flow (uni- or bidirectional).
© Copyright Policy
Related In: Results  -  Collection

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getmorefigures.php?uid=PMC2553519&req=5

pone-0003303-g017: Cladogram of Dinosauria showing the four-phase model for evolution of avian air sacs and lung ventilation within Theropoda.Phase I (Theropoda), variable posterior extension of paraxial cervical air sacs. Phase II (Tetanurae), elaboration of cranial (clavicular) and caudal (abdominal) intrathoracic air sac divisions and subcutaneous diverticulae. Phase III (Maniraptoriformes), primitive costosternal ventilatory pump. Phase IV (Maniraptora), advanced costosternal ventilatory pump. Abbreviations: aas, abdominal air sac; cas, cervical air sac; caas, caudal air sacs; clas, clavicular air sac; cor, coracoid; cras, cranial air sacs; lu, lung; sr, sternal rib; st, sternum; up, uncinate process; vr, vertebral rib. Bold arrow on lung indicates flow-through lung ventilation; question mark indicates uncertainty in the direction of air flow (uni- or bidirectional).
Mentions: The form of the pectoral and pelvic girdles in the holotypic skeleton clearly indicate that Aerosteon is a basal tetanuran (Figure 17). These features, which include the unexpanded crescentic coracoid, relatively broad scapular blade, relatively narrow brevis fossa and robust pubic peduncle of the ilium, and open obturator notch and large boot of the pubis, and sacrum limited to five vertebrae, closely resemble the condition in the allosauroids Allosaurus [47] and Acrocanthosaurus [49], [50], [54]. The small prefrontal and triradiate postorbital, which shows no development of a swollen brow or infraorbital flange, are closest to that in Allosaurus and very different from that in abelisaurids and carcharodontosaurids [15], [51].

Bottom Line: 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.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.

View Article: PubMed Central - PubMed

Affiliation: Department of Organismal Biology and Anatomy, University of Chicago, Chicago, Illinois, USA. dinosaur@uchicago.edu

ABSTRACT

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.

Methodology/principal findings: We describe a new predatory dinosaur from Upper Cretaceous rocks in Argentina, Aerosteon riocoloradensis 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.

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: (1) Phase I-Elaboration of paraxial cervical air sacs in basal theropods no later than the earliest Late Triassic. (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. (3) Phase III-Evolution of a primitive costosternal pump in maniraptoriform theropods before the close of the Jurassic. (4) Phase IV-Evolution of an advanced costosternal pump in maniraptoran theropods before the close of the Jurassic. In addition, we conclude: (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. (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.

Show MeSH
Related in: MedlinePlus