Breathing in a box: Constraints on lung ventilation in giant pterosaurs

Abstract

Pterosaurs were the first vertebrates to achieve active flight, with some derived forms reaching enormous size. Accumulating fossil evidence confirms earlier indications that selection for large size in these flying forms resulted in a light, yet strong skeleton characterized by fusion of many bones of the trunk. However, this process also added mechanical constraints on the mobility of the thorax of large pterosaurs that likely limited the options available for lung ventilation. We present an alternative hypothesis to recent suggestions of an avian‐like mechanism of costosternal pumping as the primary means of aspiration. An analysis of the joints among the vertebrae, ribs, sternum, and pectoral girdle of large pterosaurs indicates limited mobility of the ribcage and sternum. Comparisons with modes of lung ventilation in extant amniotes suggests that the stiffened thorax, coupled with mobile gastralia and prepubic bones, may be most consistent with an extracostal mechanism for lung ventilation in large pterodactyloids, perhaps similar to a crocodile‐like visceral displacement system Anat Rec, 297:2233–2253, 2014. © 2013 Wiley Periodicals, Inc.

Rib kinematics during lung ventilation in the American alligator (Alligator mississippiensis): an XROMM analysis

“…The transition of the parapophysis from the vertebral centrum to the transverse process has been well documented within crocodylians ( Claessens, 2009b ; Schachner et al, 2009 ), and also in fossil archosaurs ( Ewer, 1965 ; Piechowski and Dzik, 2010 ; Schachner et al, 2011 ; Geist et al, 2014 ). This bicondylar articulation is thought to act as a hinge joint ( Claessens, 2009b ), and so the cranial vertebral ribs would be expected to move mostly with pump and bucket handle motion, and the caudal ribs mostly with pump and calliper motion, although until now the explicit consequences of this shift for rib rotation have not been experimentally tested.…”

Vertebral morphometrics and lung structure in non-avian dinosaurs

“…Pterosaurs, the ornithodiran outgroup to dinosauriforms, have been reconstructed as having an avian-style respiratory system based on the presence of unambiguous PSP and inferred air sacs [ 59 , 60 ]. Their costovertebral morphology has been described as ‘crocodilian-like', as the parapophysis migrates dorsally to lie on or at the base of the transverse process, and it has been suggested that pterosaurs therefore had more compliant, more homogeneous lungs [ 61 ]. However, the parapophysis also migrates dorsally towards the transverse process in many dinosaurian taxa, and our results showed greater similarity between dinosaurs and birds rather than dinosaurs and crocodilians.…”

Review of taxonomy, geographic distribution, and paleoenvironments of Azhdarchidae (Pterosauria)

“…Concerning the Chinese “tapejarids,” the presence of T-shaped wing phalanges have never been demonstrated for them, and it was explicitly stated that the lack of this feature exclude them from Azhdarchidae ( Lü et al 2006 : 321). SMNK 3843 was previously identified as a possible tapejaroid ( Frey et al 2003 : fig.1c), non-azhdarchid azhdarchoid ( Elgin and Campos 2012 ), or an azhdarchid ( Geist et al in press ). The scapulacoracoid of SMNK PAL 3843 has a coracoid flange rather than a tubercle and is more similar to that of azhdarchids ( Frey et al 2003 : fig.…”