Amphicoelias fragillimus Discovered and studied in the late 1800s, Amphicoelias

Question

Amphicoelias fragillimus Discovered and studied in the late 1800s, Amphicoelias fragillimus is one of the largest known vertebrate species. The adult size is estimated to be 40-60 meters (130-200 ft in length and 122 tons in weight. Based on anatomical estimates, the brain of A. fragillimus is 16 m above the heart, and their feet are 6 m below their heart when standing. Despite its massive size, it is assumed that all the physiological systems of the species are efficient such that they survived natural selection during Jurassic Period. Design a circulatory system that allows for efficient bulk transport of blood to the tissues (1) What type of heart do you think it had based on the hearts of existing species (number of atria, ventricles, separation of the chambers, types of myocardium) (2) How was blood pressure adjusted in response to the shifts in the head position relative to the heart? 3) How did gravity affect the blood pressure in different parts of the body? 4) Does your design of the circulatory system change if A. fragillimus turned out to be an aquatic species?

Explanation / Answer

The Amphicelias likely had a 4 chambered heart- 2 ventricles and atria divided by a septum along with one large aorta like tube in lieu. This was more similar to the mammals than the reptiles. The heart was cement like. The myocardium was thick to provide for the increased metabolic needs of the large organism. Since the head is much above the heart, the pressure must've been higher when it was held erect and normalized when it was at the same level as the heart. Though much hasn't been found out regarding this topic, it is likely that certain adjustive mechanisms must have existed to maintain the blood pressure according to the head position. Gravity plays a role in the regulation of blood pressure. The venous return of such a large organism must have been significantly lower than ours. To counteract with this, either a stronger larger heart or efficient venous pumps must have been present. The head must also have received high blood pressure to prevent the siphoning of blood from the head to the lower body. Yes, it completely changes if the organism becomes aquatic.

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