Cardio‐pulmonary anatomy in theropod dinosaurs: Implications from extant archosaurs

Abstract

Although crocodilian lung and cardiovascular organs are markedly less specialized than the avian heart and lung air-sac system, all living archosaurs possess four-chambered hearts and heterogeneously vascularized, faveolar lungs. In birds, normal lung function requires extensive, dorsally situated nonvascularized abdominal air-sacs ventilated by an expansive sternum and specially hinged costal ribs. The thin walled and voluminous abdominal air-sacs are supported laterally and caudally to prevent inward (paradoxical) collapse during generation of negative (inhalatory) pressure: the synsacrum, posteriorly directed, laterally open pubes and specialized femoral-thigh complex provide requisite support and largely prevent inhalatory collapse. In comparison, theropod dinosaurs probably lacked similarly enlarged abdominal air-sacs, and skeleto-muscular modifications consistent with their ventilation. In the absence of enlarged, functional abdominal air-sacs, theropods were unlikely to have possessed a specialized bird-like, air-sac lung. The likely absence of bird-like pulmonary function in theropods is inconsistent with suggestions of cardiovascular anatomy more sophisticated than that of modern crocodilians.

A large enantiornithine bird from the Lower Cretaceous of China and its implication for lung ventilation

“…Changes in trunk volume, resulting from movements of the sternum and ribs, create pressure differences for lung ventilation. Anatomical features, such as the location of parapophysis and diapophysis on the thoracic vertebrals, uncinate processes and corresponding muscles, bicapitate vertebral ribs, length difference among sternal ribs, and bicondylar sternocostal joint, contribute to greater volumetric changes in the caudal half of the trunk, a key characteristic essential for establishing flow‐through ventilation in birds (Codd et al ., ; Claessens, ; Quick & Ruben, ). In living birds, the parapophyses lie ventral and cranial to the diapophyses (Fig.…”

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

“…In extant birds, costal ventilation has been modified such that expansion and contraction of the thorax results primarily from dorsoventral rotation of the sternum, while the lateral expansion of the ribcage is relatively limited. In the avian ribcage, a variable number of vertebral ribs (typically between 4 and 8) articulate via fibroelastic joints with stout, well‐ossified sternal ribs, which in turn contact the lateral margins of the sternal plate by means of robust, virtually bicapitate synovial hinge joints (Hillenius and Ruben, ; Perry et al, ; Claessens, ; Quick and Ruben, ). Avian sternal ribs are progressively longer caudally, and the joint angles between vertebral and sternal rib segments are increasingly acute.…”

“…Furthermore, in the Claessens et al () model the contacts between sternal ribs and the sternum would likely have formed well‐defined articulations, perhaps even robust double‐headed hinge joints as in modern birds (cf. Hillenius and Ruben, ; Claessens, ; Quick and Ruben, ). Instead, pterosaur sterna invariably have thin lateral edges, especially in contrast to the strongly reinforced area of the crista where the scapulocoracoids articulated and the majority of the flight musculature presumably attached (Fig.…”

Anatomy of the heart of the leatherback turtle

“…Here we undertook an anatomical study of the hearts of two large leatherback turtles to assess whether the leatherback heart is typical of chelonians or has features similar to monitors and pythons. Should the latter be the case, it is likely that the leatherback ventricle has pressure separation which is considered a prerequisite for high metabolic rates (Quick & Ruben, 2009; Lovegrove, 2019; Grigg et al ., 2021).…”