Hearts, neck posture and metabolic intensity of sauropod dinosaurs

Hypothesized upright neck postures in sauropod dinosaurs require systemic a rterial blood pressures reaching 700 mmHg at the heart. Recent data on vent ricular wall stress indicate chat their left ventricles would have weighed 15 times those of similarly sized whales. Such dimensionally, energetically and mechanically disadvantageous ventricles were highly unlikely in an end othermic sauropod. Accessory hearts or a siphon mechanism, with sub-atmosph eric blood pressures in the head, were also not feasible. If the blood flow requirements of sauropods were typical of ectotherms, the left-ventricular blood volume and mass would have been smaller; nevertheless, the heart wou ld have suffered the serious mechanical disadvantage of thick walls. It is doubtful that any large sauropod could have raised its neck vertically and endured high arterial blood pressure, and it certainly could not if it had high metabolic rates characteristic of endotherms.