About of dinosaur. That is the long neck. According

About 200 million years ago, the first true sauropods on the arose. Fifty million years later, by the late Jurassic, sauropods widely spread around the world. The name sauropods mean “lizard foot” in Greek. Sauropods is a group of four-legged herbivore with long neck and small skull. It’s also one of the most recognizable groups of dinosaur due to its enormous size, long neck, and tail. Known as a group includes the largest animals have ever lived on land, sauropods were always compared with whales especially blue whale, which is the largest extant animal on earth. However, besides its size, there is a mother remarkable characteristic makes it stand out from other groups of dinosaur. That is the long neck. 
    According to the collection of specimens, paleobiologists found that sauropod necks could be over 50 feet in length, which is six times longer than a giraffe neck. One of the theory is sauropods necks evolved for high browsing. The long neck helps reach to higher plants, also prevent competition between different groups of dinosaur while feeding themselves. There are also clues hidden in sauropod skeleton. Brachiosaurs, unlike most other sauropods, had long forelimbs that caused an unusual shape of its back. Paleobiologist believes, in accordance with the discovered fossil record, brachiosaur neck and its body are in a fairly straight line, this indicated that its neck was pointing upwards. However, there is evidence indicates that sauropod necks were adopted for low browsing. 
Some paleobiologists believe that low browsing was an energetically attractive option for sauropods. It reduced the loss of energy while sauropods moving around searching food with their gigantic body, and when they lift their necks for food. According to Wilkinson and Graeme Ruxton’s study in the journal Biology Letters, for Brachiosaurus, low browsing reduces time and energy consumption of foraging by 80 percent with its approximately 8 meters long neck. Besides these suppositions, there is also thesis suggests that sauropod necks were sexual signals. The idea is that male sauropods with bigger protuberances were more attractive to females. However, how can sauropods lived with necks six times longer than giraffe’s without losing balance, what the reason that sauropods can have such long necks?
The first reason is sauropods had small and light heads compared to their necks. Sauropods head only adapted to sheer plants but not obtain them, so there’s no need for extra places which might increase body mass. Brachiosaurus, as an example, has incredible long necks estimated that in length of 8.5 meters, its head is only as big as a single cervical vertebra. Sauropod gigantic torso size also provides a strong base for the neck. Its large torso not only can support a heavy neck but also help balance the whole body while its neck extends farther away. This also enlarges the feeding range of Sauropods. 
To carry sauropods necks, their vertebrae are hollow but strong, like bird’s bone. As Michael Taylor and Mathew Wedel explain in the article Why sauropods had long necks; and why giraffes have short necks, “In effect, sauropods inflated their vertebrae within the muscular envelope of the neck, moving the bone, muscle and ligament away from the center so that they acted with greater mechanical advantage.” Also, there’s a super long windpipe in sauropod neck to bring air to the lungs. Usually, mammals need a short trachea to get enough amount of oxygen to lungs for breathing, but by having an advantage of hollow vertebrae, an air sac system was formed in the whole neck rather than just the windpipe.
Brachiosaurus, an African species of sauropod dinosaur, once had a name called Giraffatitan, which means “giant giraffe”. It is reasonable that this kind of dinosaur was named after giraffe since they all have long necks and both giant to people; but why giraffe has such a short neck compare to Brachiosaurus lived in 150 million years ago?
First of all, it’s obviously impossible for an animal of the same size as a giraffe carry a huge neck like a sauropod dinosaur. J. Michael Parrish’ suggests that neck length is positively allometric with respect to body size in sauropods, varying with torso length to the power 1.35. (2006. The origins of high browsing and the effects of phylogeny and scaling on neck length in sauropodomorphs, p. 213) According to the calculation, giraffe torso is capable of carrying a neck around 2.5 meters long. Although its neck is much shorter than sauropods, giraffe has long trachea as well. Instead of the air sac system that sauropods had, giraffe has evolved a heart that larger than a human’s heart since it has to pump oxygen-rich blood up to its brain from the lungs. This process takes about twice times as the normal pressure needed for the human heart to pump blood to a human brain. 
25 million years ago, Prodremotherium, the ancestor of modern giraffe arose. Unlike sauropods, paleobiologist is more certain about the fact that how giraffe was evolved from its ancestor. Darwin was the first naturalist propose that giraffe got its long neck in the process of natural selection. When a large number of animals live in the same environment, the shortage of food will become a huge problem for them to survive. Ancestors of giraffe had gone through this situation millions of year ago. Those which had longer necks than the others could reach the higher part of plants for food, and then they survived, bred, and evolved into giraffe we see today. Although sauropods are no longer exist, we can still speculate the behavior and evolution of sauropods by studying fossil records or even extant animals which similar to sauropods like the giraffe.

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