If a giraffe's neck only has seven vertebrae, how is it so flexible?

Thanks to their towering necks, giraffes can grow as tall as 19 feet (6 meters).
Thanks to their towering necks, giraffes can grow as tall as 19 feet (6 meters).
Anup Shah/Getty Images

Giraffes tower above all other mammals in the world. Loping along the African savannas on skinny, stiltlike legs, adult male giraffes can top out at 19 feet (6 meters) [source: National Geographic]. But only around half of that height comes from their stems -- the rest is all neck. Then, if all of that length wasn't enough for these spotted giants, they have yet another tool to expand their reach. Giraffes' tongues can stretch as far as 18 inches (46 centimeters) to snag even the highest hanging leaf [source: San Diego Zoo].

In regard to the long neck, scientists continue to scratch their heads about the exact evolutionary path the animal's ancestors took to instigate such a unique adaptation. One of the most compelling pieces of this puzzle is that the great expanse of neck contains a mere seven vertebrae. That's the same number of vertebrae that humans and almost all other mammals have.

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For an explanation, many point to giraffes' preferred snack of acacia leaves, which would make the added extension necessary for craning to the tops of these 20-foot (6-meter) trees. However, giraffes also spend time, particularly during the later part of the day, with their legs splayed out, munching on grasses and low-lying shrubs [source: Dagg and Foster].

Or perhaps it came about to impress the shorter-necked ladies. Giraffe males, called bulls, will duke it out in a neck-to-neck competition for female giraffes. Similar to rams locking horns in heated battles, the bulls use their hefty necks to strike each other with crushing force. Survival of the fittest would suggest that the ones with the longest and strongest would win.

Whatever the case, those seven vertebrae dwarf the ones found in our bodies. In fact, each giraffe neck vertebra may be as long as 10 inches (25 centimeters) [source: San Diego Zoo]. As you can guess, that doesn't exactly make for a light load to tote. Stack up those seven blocks of bone and toss on a head, and we're talking around 600 pounds (272 kilograms) of cargo [source: San Diego Zoo].

How do these lanky quadrupeds support their upper halves, much less move them around? Go on to the next page to find out the secrets inside nature's longest neck.

Anatomy of a Giraffe

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Certain characteristics of giraffe necks give them a flexibility rivaling any Slinky. The first feature is the way that the vertebrae in the neck, called the cervical vertebrae, are joined together. Remember that giraffes have seven of these bones, just like we do. However, giraffe cervical vertebrae are bound together with ball-and-socket joints [source: Owen]. These are the kinds of joints that link your arm with your shoulder and offer a 360-degree range of motion. Also, the joint between its neck and skull permits the giraffe to extend its head almost completely perpendicular to the ground.

Moving down to where the neck meets the back, we find the second important anatomical feature for the giraffe's slinkiness. We call the vertebrae in the top portion of our backs the thoracic vertebrae. In humans, thoracic vertebrae are joined at the middle of the bone to provide added stability; and our cervical vertebrae fuse at the front and back for more mobility. Giraffe anatomy doesn't follow this same construction, and its first and second thoracic vertebrae are bound in the same way that its cervical ones are, with ball-and-socket joints [source: Dagg and Foster]. That adaptation gives the giraffe an extra point of flexibility. It also accounts for the giraffe's signature hump [source: Encarta].

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This highly flexible, yet heavy, body part is integral to the gangly animal's movement. Watch a giraffe and you'll notice that the neck moves back and forth with its stride. That's because the weight and motion of the neck guides the giraffe's center of gravity [source: Dagg and Foster]. The animal also tosses its neck to and fro to help it rise to a standing position on its spindly legs. You can compare this to when we swing our arms up over our head to pull us out of bed in the morning.

Strrreeetttcch!
Strrreeetttcch!
Manoj Shah/Getty Images

As another result of the long neck, a giraffe's blood has a long journey to travel. For that reason, the anatomy of a giraffe is quite amazing. The animal has a specialized cardiovascular system that keeps blood moving adequately to the brain and heart when it moves its neck and head around, ensuring that bending down to take a sip of water won't cause a possibly lethal head rush [source: Dagg and Foster]. Giraffes' blood vessels are equipped with valves that prevent blood from backtracking due to gravity [source: Wood and Johansen]. They also have a higher concentration of red blood cells, larger hearts and tighter skin, especially around their legs, which help circulate blood better [source: Dagg and Foster].

Keeping everything chugging along, the giraffe also breathes at a relatively slow rate. Its enlarged lungs compensate for the trachea's extensive length, as the air travels up that long highway of a neck.

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Sources

  • Calder, William A. "Size, Function, and Life History." Courier Dover Publications. 1996. (July 10, 2008)http://books.google.com/books?id=ymLBZWGM7KEC
  • Chudler, Eric. "The Spinal Chord." Neuroscience for Kids. University of Washington. (July 11, 2008)http://faculty.washington.edu/chudler/spinal.html
  • Dagg, Anne Innis and Foster, J. Bristol. "The Giraffe: Its Biology, Behavior, and Ecology." Robert E. Krieger Publishing Company. 1982.
  • "Giraffe." Encarta. (July 10, 2008)http://encarta.msn.com/encyclopedia_761561060/giraffe.html
  • "Giraffe." National Geographic. (July 10, 2008)http://animals.nationalgeographic.com/animals/mammals/giraffe.html
  • "How the Giraffe Got Its Neck." Discover Magazine. March 1, 1997. (July 10, 2008)http://discovermagazine.com/1997/mar/howthegiraffegot1084/?searchterm=giraffe
  • "Mammals: Giraffe." San Diego Zoo. (July 10, 2008)http://www.sandiegozoo.org/animalbytes/t-giraffe.html
  • Owen, Jennifer. "Feeding Strategy." University of Chicago Press. 1982. (July 10, 2008)http://books.google.com/books?id=RwMDI06snIwC
  • Wood, Stephen C. and Johansen, Kjell. "Physiological Adaptations in Vertebrates: Respiration, Circulation and Metabolism." CRC Press. 1991. (July 10, 2008)http://books.google.com/books?id=-MCP3vAx1zkC
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