The giraffe is a mammal, therefore much of its anatomy is similar to that of other mammals. Like most other mammals, the giraffe has seven neck bones. What if it did not have seven bones between the shoulders and the base of the skull? Man's short neck supports a perfectly balanced head in the erect posture with very little effort. The giraffe's huge head must be held aloft at all times.
No. It can lower it's head when it has a mind to.
When standing, nearly half of its approximately 225-kilogram (500 pound) neck muscles are in tension. The amount of muscle required is directly related to the number of joints that must be supported.
No. It's directly related to the mass of the neck and head, adjusted for the distribution of the mass from the proximal end of the neck. The number of joints is not a constraint. However if giraffes evolved from smaller mammals, changing the number of neck vertebrae would be a major change, and difficult evolutionarily. We would expect this to remain the same, and it does.
Reducing the joints to just two, at the skull and at the chest, would reduce the weight considerably and require less energy for survival.
Nope. the weight would not be greatly affected, but flexibility woud suffer greatly.
If the shortage of food drove the neck to change, would not the number of neck bones and joints be changeable also by such evolutionary processes? Of course the problem with this design would be a loss of flexibility, and would severely increase breakability if the giraffe received a blow to the head or neck.
Yes. Which is why we see an evolutionary solution, not a redesign.
In the same respect, having a megajointed neck would require the exact opposite - greater energy use and greater muscle mass to be supported.
No. That's wrong.
This would cause the giraffe's centre of gravity to shift ahead of the front legs when the head is extended straight forward, causing the hind legs to come off the ground - assuming the front legs were strong enough. Seven neck bones is excellent design.
It also happens to be the same number as the animals from which giraffes evolved. How about that?
With the head being so high in the air, the huge heart of the giraffe must be capable of delivering sufficient oxygen-rich blood three metres (10 feet) up to the brain. This would be a problem (involving too high blood pressure) when the giraffe was head-down drinking water, were it not for a unique collection of reinforced artery walls, by-pass and antipooling valves, a web of small blood vessels (the rete mirabile, or 'marvellous net') and pressure-sensing signals that keep adequate blood flow to the brain at just the right pressure. Even to those who consider this as just 'adaptation to high gravitational pressures in its cardiovascular system', the giraffe is unique.
No, it's not unique. Many mammals have a rete, and the valves are found in all mammals as well. They are just more robust in giraffes, which is to be expected.
The giraffe's heart is probably the most powerful among animals, because about double normal pressure is required to pump blood up the giraffe's long neck to the brain.
Equally marvellous is the fact the blood does not pool in the legs, and a giraffe does not bleed profusely if cut on the leg. The secret lies in an extremely tough skin and an inner fascia that prevents blood pooling. This skin combination has been studied extensively by NASA scientists in their development of gravity-suits for astronauts.
No kidding? Got a checkable source for that? You see, those valves are found in the legs, too. You have them also, but again, not as robust.It quickly becomes apparent that these unique facets of the giraffe are all interactive and interdependent with its long neck.
Yep, as giraffes gradually got bigger (we have plenty of intermediate ones in the fossil record) they adapted to larger size.
But there's more. The smaller red blood cells allow for more surface area and a higher and faster absorption of oxygen into the blood. This helps to retain adequate oxygen to all extremities, including the head.
The lungs work in conjunction with the heart to supply the giraffe with the necessary oxygen, but in a way that is unique to the giraffe. The giraffe's lungs are eight times the size of those of humans, and its respiratory rate is about one-third that of humans. Breathing more slowly is necessary in order to exchange the required large volume of air without causing windburn to the giraffe's rippled 3.6 metres (12 feet) of trachea. When the animal takes in a fresh breath, the oxygen-depleted previous breath cannot be totally expelled. For the giraffe this problem is compounded by the long trachea that will retain more dead air than man can inhale in one breath. There must be enough lung volume to make this 'bad air' a small percentage of the total. This is a physics problem that the giraffe has solved.
The giraffe has larger lungs because of its greater size. Because the tidal volume is so great, it was possible to evolve a long neck. If evolutionary theory is correct, smaller giraffes should have relatively shorter necks. They do.
Ecologically, the giraffe is perfectly matched to its environment.
See Darwin to find out why.
There is need of a tree trimmer to keep the fast-growing shade trees from overshadowing the ground and killing the much needed grass that provides food for the other savanna animals.
The trees on the savannah are sparse, and relatively small compared to open grassland. Shade is actually good for grass in that sunny environment. And giraffes generally do not feed on trees, but on lower vegetation.
To suggest that all of this could have evolved in one class of animal,
Do you know what a "class" is?
lacking any conceivable close relatives,
Wrong again. There are numerous fossil giraffes, and at least two living giraffoids, the pronghorn antelope and the okapi. The lengths of their necks is what one would expect, based on their size. Allometry shows that larger giraffes have relatively longer necks.
and becoming so developed solely due to a supposed lack of food at ground level, is preposterous.
Sure is. But that's not why the long neck evolved. The reason others didn't copy the giraffe is because that niche was already occupied. So other species found other niches, or became extinct.
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