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Giraffe at Augrabies

Category: Organisms
Posted on: November 8, 2007 4:30 PM, by Greg Laden

Giraffa camelopardalis .. the tallest of all land animals.

It is said that giraffes evolved a long neck in order to feed off the top of trees, avoiding competition with other browsing mammals. However, most leaves are actually eaten by insects who can get to these leaves as well as any other. Personally, I think the long neck is an adaptation to having very long legs. The long neck allows the giraffe to reach water without having to get too far down on the ground or lay on its side.

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Comments

Greg said: "Personally, I think the long neck is an adaptation to having very long legs."

Then why the long legs (especially if one needs a later adaptation to make them practical)?

Posted by: Son of Priam | November 8, 2007 5:03 PM

I don't think it's out yet, but I've heard that an intermediate fossil giraffe that was recently found, it's neck being between that of an okapi and a giraffe when compared to body size. Overall, I think sexual selection probably played an important role in the development of long necks, which proved to be useful in terms of obtaining a greater range of food resources (giraffes feed at varying levels), perhaps longer necks being advantageous on more than one level. The fact that the rest of the body has adaptations that go along with the long neck (long legs, rete mirable to keep the blood pressure to the head up) suggest a more gradual change due to functional importance, but the evolution of the long neck of the giraffe still seems to be enigmatic. Also, sexual selection has been proposed as the primary reason for long necks in the past, but such cases usually center around the male-male competitions, which don't really explain how the trait evolved (even if it can be correlated to what the animals are doing now).

Posted by: Laelaps | November 8, 2007 5:12 PM

They certainly do use their necks in sexual competition, but as you point out, it is not a dimorphic trait.

Let me know about that new fossil when it is finally outed!

Posted by: Greg Laden | November 8, 2007 5:54 PM

I guess their legs are long for precisely the same reason: to reach the ground. But the question that remains is why the ground is so darned far away.

The only plausible explanation I've read matches that explaining why hyenas' jaws can crack thighbones: they don't normally need to, but in a tough year it makes all the difference.

Posted by: Nathan Myers | November 8, 2007 7:20 PM

Are you serious Greg?

Posted by: Kev | November 9, 2007 7:40 AM

the giraffe is one of my favorite animals to visit in our zoo. we have six adults and two calves. they have quite a big area to roam. their roommates are ostridges. the giraffes are always chasing them. i have not asked the zoo why. maybe here's why. they can't catch them!

Posted by: PetMono | November 9, 2007 3:38 PM

Kev:

Yes. If you look at an Okapi, it has very long legs and a slightly long neck. When I watch giraffes or from what I've read about, the part of their phenotype that seems to make the most difference in terms of locomotion, feeding, and predator avoidance seems to be their long legs, much more than their long necks.

Surely, it is both that make their mouths able to be way up there at the top of the trees. Also, they would just look stupid if they had long necks and short legs, so that would obviously select against them :)

Posted by: Greg Laden | November 9, 2007 6:51 PM