Australia: The Land Where Time Began

A biography of the Australian continent 

Dinosaurs - Sauropod Necks

According to Manning some of the sauropods found in China had necks that were more than half the length of their entire body, The neck of Daxiatitan was longer than the entire body length of T. rex. Each of its fossilised neck bones were extremely heavy. It had 19 neck vertebrae compared to 7 in most mammals. To move such a neck Manning suggests it needed huge muscle power, a rib on each side of each vertebrae provided attachment sites for these muscles, as well as providing structural support. At the base of the neck were ribs, some longer than a man,  that aided in lifting the large weight of the neck. Daxiatitan demonstrated how the anatomy of very large dinosaurs was adapted to grow such long necks. According to Manning, theoretically the necks could have kept growing with the help of neck ribs.

The tiny brain at the end of the neck would have required a powerful, large heart to pump blood far enough. He suggested the length of the necks could be limited by the maximum size of the heart. To get an idea of how they may have managed the high blood pressure when they lowered their heads to drink he studied the way giraffes managed the same problem. In the giraffe there is a mesh of blood vessels near the base of the skull that divided the main arterial blood flow into many smaller flows that were each at lower pressure than the main blood flow, so the blood reaching the brain was at a manageable pressure even when the heed was lowered.

Experiments Manning carried out with a firetruck indicated that a large sauropod would need a heart the size of 2 VW beetles and use more energy than was used by the rest of the body to power it. The blood pressure of a giraffe is twice that of a human and the sauropod would need a pressure twice that of a giraffe. When he ran software "dinomorph" written by Kent Steven it suggested that in life sauropod necks were held horizontal, and according to Steven there is no evidence suggesting they were held high. See Dinosaur Biology - General Anatomy.  If this was indeed the case there would be no problem with heart size and pumping power. One of the largest dinosaurs in North America was Supersaurus, it had the largest back vertebrae known. As with the bones of other sauropods it had pneumatic bones, the larger the sauropod the larger the air spaces in the bones. A mammal vertebra the size of a Supersaurus vertebra would need a fork lift to carry it, the Supersaurus vertebra can be carried  by a man. The neck bones of the larger sauropods had up to 90 % of each vertebra taken up by air spaces.

Another requirement of very large size is getting enough oxygen to the brain at the end of the long neck. Birds get fresh air into the lungs both when they inhale and exhale due to their much more efficient respiratory system than that of mammals that only get fresh air into the lungs when they inhale. The intricate system of air sacs in the respiratory system of birds extracts twice as much oxygen from each breath than do mammals. The conclusion of this is that birds and dinosaurs can have long necks, and in the case of dinosaurs, very large bodies, because of their very efficient respiratory system.

Manning used finite element analysis (FEA) and technology form the oil industry to measure the thickness of actual bone in the femur of Argentinosaurus, the largest dinosaur known at the time of writing, weighing about 90 tonnes. Based on the bone thickness measured for Argentinosaurus with an estimated weight of about 90 tonnes he used FEA to estimate the weight bearing capacity of bone for various sized sauropods up to more then 400 tonnes. FEA concluded that the largest sauropod that could be possible, and still be able to walk, is 120 tonnes.

Sources & Further reading

  1. Manning, Phillip, 2011, Jurassic CSI, National Geographic DVD

Links

  1. Dinodata
  2. Images of Argentinosaurus

 

Author: M. H. Monroe
Email:  admin@austhrutime.com
Last Updated 18/01/2012 

 

 

 

 

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                                                                                           Author: M.H.Monroe  Email: admin@austhrutime.com     Sources & Further reading