Oolon Colluphid
25 Feb 2009, 01:55 PM
Whoo-hoo! I get to make the first thread! So it may as well be to report this (even if I only have me to talk to about it :D)...
Respiratory evolution facilitated the origin of pterosaur flight and aerial gigantism
Claessens, O'Connor and Unwin
PLoS 2009; 4(2): e4497. Epub 2009 Feb 18 (http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0004497)
Pterosaurs, enigmatic extinct Mesozoic reptiles, were the first vertebrates to achieve true flapping flight. Various lines of evidence provide strong support for highly efficient wing design, control, and flight capabilities. However, little is known of the pulmonary system that powered flight in pterosaurs. We investigated the structure and function of the pterosaurian breathing apparatus through a broad scale comparative study of respiratory structure and function in living and extinct archosaurs, using computer-assisted tomographic (CT) scanning of pterosaur and bird skeletal remains, cineradiographic (X-ray film) studies of the skeletal breathing pump in extant birds and alligators, and study of skeletal structure in historic fossil specimens. In this report we present various lines of skeletal evidence that indicate that pterosaurs had a highly effective flow-through respiratory system, capable of sustaining powered flight, predating the appearance of an analogous breathing system in birds by approximately seventy million years. Convergent evolution of gigantism in several Cretaceous pterosaur lineages was made possible through body density reduction by expansion of the pulmonary air sac system throughout the trunk and the distal limb girdle skeleton, highlighting the importance of respiratory adaptations in pterosaur evolution, and the dramatic effect of the release of physical constraints on morphological diversification and evolutionary radiation.
Or in short, birds aren't the only ones with this cool -- and much more efficient than the mammalian version -- adaptation.
Figure 1. Micro-computed tomographic (CT) scans and photograph illustrating external pneumatic openings and typical pneumatic architecture in the ornithocheirid pterosaur Anhanguera santanae.
http://www.plosone.org/article/fetchObject.action?uri=info%3Adoi%2F10.1371%2Fjour nal.pone.0004497.g001&representation=PNG_M
Figure 3. Models of ventilatory kinematics and the pulmonary air sac system of pterosaurs.
http://www.plosone.org/article/fetchObject.action?uri=info%3Adoi%2F10.1371%2Fjour nal.pone.0004497.g003&representation=PNG_M
a, Model of ventilatory kinematics in Rhamphorhynchus. Thoracic [chest] movement induced by the ventral [front/underside] intercostal [between the ribs] musculature results in forward and outward displacement of the distal [further out] vertebral and proximal sternal ribs, and ventral displacement of the sternum, upon inspiration [breathing in] (blue arrows and pink outline). In addition, ventral expansion of the abdomen is induced through caudoventral rotation of the prepubis. [...]
b, Model of ventilatory kinematics in Pteranodon wherein the fused anterior [front] vertebral ribs and articulation of the scapulocoracoid with the supraneural plate and anterior sternum limit movement of the anterior sternum, which cannot undergo elliptical rotation. However, the posterior vertebral ribs, sternal ribs, sternum, and prepubis are still capable of anterodorsal-posteroventral excursions facilitating volumetric increases and decreases of the thorax during inspiration-expiration. [...]
c, d, reconstruction of pulmonary air sac system in the Lower Cretaceous ornithocheirid Anhanguera santanae (AMNH 22555).
c, Lateral view showing the inferred position of the lungs (orange), cervical (green) and abdominal air sacs (blue), as predicted on the basis of postcranial skeletal pneumaticity. Thoracic air sacs (shown in grey) are also likely to have been present, but generally do not leave a distinct osteological trace. Humerus and more distal forelimb not shown.
d, Dorsal view illustrating the inferred position of subcutaneous diverticular networks (light blue) distally along the wing. The right side depicts a conservative estimate for the size of the airsac network, limiting it to the pre-axial margin of the wing based solely on the presence of pneumatic foramina in closely positioned wing bones. The left side depicts the likely maximal size of an inferred diverticular network, accounting for its inclusion between the dorsal and ventral layers of the wing membrane. Scale = 10 cm. [...]
Conclusions
The evidence for a lung-air sac system and a precisely controlled skeletal breathing pump supports a flow-through pulmonary ventilation model in pterosaurs, analogous to that of birds. The relatively high efficiency of flow-through ventilation was likely one of the key developments in pterosaur evolution, providing them with the respiratory and metabolic potential for active flapping flight and colonization of the Late Triassic skies. This interpretation is consistent with other lines of evidence supporting relatively high metabolic rates in pterosaurs, including the filamentous nature of the integument, a flight performance comparable to that of extant birds and bats and relatively large brain size. The expansion of a subcutaneous air sac system in the forelimb facilitated the evolution of gigantism in several derived pterodactyloid groups and resulted in the emergence of the largest flying vertebrates that ever existed.
******
For more on the advantages of through-flow lungs compared to our own, see the (relatively straightforward) paper: The human lung: did evolution get it wrong? (http://www.erj.ersjournals.com/cgi/content/full/29/1/11)
Respiratory evolution facilitated the origin of pterosaur flight and aerial gigantism
Claessens, O'Connor and Unwin
PLoS 2009; 4(2): e4497. Epub 2009 Feb 18 (http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0004497)
Pterosaurs, enigmatic extinct Mesozoic reptiles, were the first vertebrates to achieve true flapping flight. Various lines of evidence provide strong support for highly efficient wing design, control, and flight capabilities. However, little is known of the pulmonary system that powered flight in pterosaurs. We investigated the structure and function of the pterosaurian breathing apparatus through a broad scale comparative study of respiratory structure and function in living and extinct archosaurs, using computer-assisted tomographic (CT) scanning of pterosaur and bird skeletal remains, cineradiographic (X-ray film) studies of the skeletal breathing pump in extant birds and alligators, and study of skeletal structure in historic fossil specimens. In this report we present various lines of skeletal evidence that indicate that pterosaurs had a highly effective flow-through respiratory system, capable of sustaining powered flight, predating the appearance of an analogous breathing system in birds by approximately seventy million years. Convergent evolution of gigantism in several Cretaceous pterosaur lineages was made possible through body density reduction by expansion of the pulmonary air sac system throughout the trunk and the distal limb girdle skeleton, highlighting the importance of respiratory adaptations in pterosaur evolution, and the dramatic effect of the release of physical constraints on morphological diversification and evolutionary radiation.
Or in short, birds aren't the only ones with this cool -- and much more efficient than the mammalian version -- adaptation.
Figure 1. Micro-computed tomographic (CT) scans and photograph illustrating external pneumatic openings and typical pneumatic architecture in the ornithocheirid pterosaur Anhanguera santanae.
http://www.plosone.org/article/fetchObject.action?uri=info%3Adoi%2F10.1371%2Fjour nal.pone.0004497.g001&representation=PNG_M
Figure 3. Models of ventilatory kinematics and the pulmonary air sac system of pterosaurs.
http://www.plosone.org/article/fetchObject.action?uri=info%3Adoi%2F10.1371%2Fjour nal.pone.0004497.g003&representation=PNG_M
a, Model of ventilatory kinematics in Rhamphorhynchus. Thoracic [chest] movement induced by the ventral [front/underside] intercostal [between the ribs] musculature results in forward and outward displacement of the distal [further out] vertebral and proximal sternal ribs, and ventral displacement of the sternum, upon inspiration [breathing in] (blue arrows and pink outline). In addition, ventral expansion of the abdomen is induced through caudoventral rotation of the prepubis. [...]
b, Model of ventilatory kinematics in Pteranodon wherein the fused anterior [front] vertebral ribs and articulation of the scapulocoracoid with the supraneural plate and anterior sternum limit movement of the anterior sternum, which cannot undergo elliptical rotation. However, the posterior vertebral ribs, sternal ribs, sternum, and prepubis are still capable of anterodorsal-posteroventral excursions facilitating volumetric increases and decreases of the thorax during inspiration-expiration. [...]
c, d, reconstruction of pulmonary air sac system in the Lower Cretaceous ornithocheirid Anhanguera santanae (AMNH 22555).
c, Lateral view showing the inferred position of the lungs (orange), cervical (green) and abdominal air sacs (blue), as predicted on the basis of postcranial skeletal pneumaticity. Thoracic air sacs (shown in grey) are also likely to have been present, but generally do not leave a distinct osteological trace. Humerus and more distal forelimb not shown.
d, Dorsal view illustrating the inferred position of subcutaneous diverticular networks (light blue) distally along the wing. The right side depicts a conservative estimate for the size of the airsac network, limiting it to the pre-axial margin of the wing based solely on the presence of pneumatic foramina in closely positioned wing bones. The left side depicts the likely maximal size of an inferred diverticular network, accounting for its inclusion between the dorsal and ventral layers of the wing membrane. Scale = 10 cm. [...]
Conclusions
The evidence for a lung-air sac system and a precisely controlled skeletal breathing pump supports a flow-through pulmonary ventilation model in pterosaurs, analogous to that of birds. The relatively high efficiency of flow-through ventilation was likely one of the key developments in pterosaur evolution, providing them with the respiratory and metabolic potential for active flapping flight and colonization of the Late Triassic skies. This interpretation is consistent with other lines of evidence supporting relatively high metabolic rates in pterosaurs, including the filamentous nature of the integument, a flight performance comparable to that of extant birds and bats and relatively large brain size. The expansion of a subcutaneous air sac system in the forelimb facilitated the evolution of gigantism in several derived pterodactyloid groups and resulted in the emergence of the largest flying vertebrates that ever existed.
******
For more on the advantages of through-flow lungs compared to our own, see the (relatively straightforward) paper: The human lung: did evolution get it wrong? (http://www.erj.ersjournals.com/cgi/content/full/29/1/11)