Birds and mammals have a four-chambered heart, with two ventricles and two atria, but other modern reptiles have a three-chambered heart, with just one ventricle. Paleontologists debate whether dinosaurs had a typical "reptile-like" heart or a "birdlike" heart. Long-necked sauropod dinosaurs could have had unusual circulatory demands because their head may have been raised far above their heart. The farther the head is above heart, the greater the systolic pressure needs to be for blood to reach the brain. For example, the long-necked dinosaur Brachiosaurus may have carried it head as much as 6 m (20 feet) above its heart. It is estimated that such an anatomy demanded a systolic blood pressure of 500 mm of mercury for blood to reach the brain! Some paleontologists consider this to be evidence that dinosaurs must have had a four-chamber heart that supported a dual circulatory system similar to that of birds and mammals, rather than the three-chambered heart of non-bird reptiles. Can you explain why?
Mammals and birds both have a four-chambered heart that keeps the oxygenated blood separated from the deoxygenated blood. Deoxygenated blood form the body enters the right atrium. Blood is then pumped from the right atrium to the right ventricle that then pumps the blood to the lungs via the pulmonary artery. Returning from the lungs, oxygenated blood entered the left atrium via the pulmonary vein. From the left atrium blood is pumped to the left ventricle and out to the body through the aorta.
In reptiles deoxygenated blood from the body enters the right atrium and is then transported into a common ventricle allowing deoxygenated blood to mix with oxygenated blood from the left atrium. From the common ventricle blood is pumped both to the ...
Several paragraphs with web references examining the rationale behind the thinking that dinosaurs had 4-chambered hearts like mammals and not 3-chambered hearts as in reptiles.