Cardiovascular Physiology of Sauropods.

Dinosaurs dominated terrestrial ecosystems for more than 160 million years under fluctuating atmospheric conditions that profoundly shaped their cardiovascular physiology. Evidence from phylogenetic bracketing, fossil morphology, and comparative models with crocodilians, birds, and mammals suggests that many dinosaurs possessed a fully separated four-chambered heart capable of sustaining high systemic pressures and efficient oxygen (O2) transport. In sauropods, extreme vertical distances between the heart and brain required arterial pressures exceeding those of any extant vertebrate, raising questions about cardiac structure, ventricular wall stress, and vascular adaptations. Oxygen transport was further modulated by atmospheric O2 variability across the Mesozoic and therefore sauropods likely managed these changes by shaping their hemoglobin affinity, capillary density, respiratory system, and Bohr and Haldane effects. Mitochondrial density, redox balance, and the regulation of reactive species such as nitric oxide and hydrogen sulfide may have already underpinned thermoregulation, metabolic reprogramming, and tissue energetics. By integrating paleophysiology with modern comparative physiology, this review discusses how informed speculations on sauropods cardiovascular biology may be used to improve our understanding of endothermy, gigantism, and adaptive strategies in variations of O2/carbon dioxide environments. We posit that the necessary adaptations of the heart, microcirculation, and pressure-volume relations are relevant for understanding extreme physiology and, in some cases, human cardiovascular disease. This review synthesizes current knowledge on sauropods cardiovascular physiology, focusing on cardiac function, vascular architecture, O2 transport, and whole-organism integration.