Unique Leg Bone Structure Helps Keep Giraffes On Their Feet

Alan McStravick and Gerard LeBlond for redOrbit.com – Your Universe Online

As one of the largest purveyors of children’s games and toys, Toys ‘Я’ Us saw the value in choosing one of the more uniquely designed creatures in the animal kingdom, the giraffe, as their spokesanimal. Noted for long legs and a long neck, the giraffe is the tallest land dwelling animal on Earth and it’s different but docile appearance has long piqued the attentions of children worldwide. Now it appears the attentions of the scientific community have also landed on the tan-speckled beast.

Weighing in at an approximate 2,200 pounds, a group of researchers based out of the Structure and Motion Lab  at the Royal Veterinary College in London wondered how the long, thin legs of the giraffe were able to support the rather robust torso of the animal. By studying the ligament structure within the legs, it appears the team found their answer.

“Giraffes are heavy animals (around 1000 kg), but have unusually skinny limb bones for an animal of this size. This means their leg bones are under high levels of mechanical stress,” lead investigator Chris Basu, of the Royal Veterinary College, explains in a statement. Speaking with the BBC Basu went on to state, “I’m interested in how giraffe have evolved from their modestly-proportioned ancestors to these bizarrely long-necked, long-legged animals that we see today.”

The relatively diminutive okapi, the smaller antelope-like creature long believed to be the early evolutionary progenitor of the giraffe, could now definitively be named as an early ancestor thanks to this research. “I’d like to link modern giraffes with fossil specimens to illustrate the process of evolution,” Basu explained. “We hypothesize that the suspensory ligament has allowed giraffes to reach large sizes that they otherwise would not have been able to achieve.”

The giraffe’s bones, which are similar to the human metatarsal or foot bone and the metacarpal or hand bone, are elongated and make up about half the total length of the leg. Along the length of these bones are grooves which contain the suspensory ligament alluded to above by Basu. Other large animals such as horses also have this type of leg structure, but this was the first time the giraffe has been studied.

This structure could explain why the giraffe’s legs can hold up their immense weight without collapsing. “It turns out,” according to professor John Hutchinson from the Royal Veterinary College, “that the suspensory ligament plays an important role.”

To test the theory, researchers accepted donated limbs from European zoos. The legs came from already deceased giraffes who had died naturally or been euthanized for unrelated circumstances. The researchers placed the limbs securely in rigid frame and by using a hydraulic press applied about 560 pounds of force to each limb to simulate the bodyweight of the giraffe. The legs remained upright and stable even under added force. The suspensory ligament is a tissue, not a muscle, so its function is for support and cannot generate any force on its own.

Relying on the suspensory ligament, rather than muscle, means this structure allows the giraffe to expend far less energy as a result. This then reduces fatigue on the animal, allowing for more efficient transport of it’s massively disproportionate frame. The team also learned that the suspensory ligament structure is an important feature in the giraffe leg for preventing damage to the feet by working to prevent overextension of the animal’s foot joints.

The majestic and graceful nature of the wild giraffe appears contradictory when you consider that its weight rivals that of some elephants and other large creatures. However, thanks to this novel research into the leg structure of these animals, we have learned it will take a lot more than skinny legs and knobby knees to keep a good giraffe down.


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