Unique, Elastic Ligament Structure Helps Giraffes Stand on Spindly Legs

Four skinny legs seem slightly inadequate to endure the weight of a 2,000 pound body. Yet for giraffes, ligament elasticity prevents these creatures from collapsing under their immense weight and height. 

"Giraffes are heavy animals (around 1000 kg), but have unusually skinny limb bones for an animal of this size" explained lead investigator Christ Basu, a PhD student in the Structure & Motion Lab at the Royal Veterinary College in the UK, via a news release. "This means their leg bones are under high levels of mechanical stress."

Researchers point out that giraffes have extremely elongated metatarsal bone (in the foot) and metacarpal bone (in the hand). A distinct groove that houses the suspensory ligament and that can also be seen in other large animals, such as horses, gives these and other creatures the ability to support heavy weights on spindly legs.

To test this theory, researchers received donations of limbs from EU zoos. These came from giraffes who had died naturally in captivity or were euthanized for reasons that were not work related. Afterward, their limbs were fixed to a rigid frame and pressured with up to 550 pounds to simulate body weight.

Study results showed that despite this weight, the limbs remained upright and stable without the need for any additional support. In fact, they could even take on more due to the elasticity of the suspensory ligament. However, because the ligament cannot generate for itself, the creatures gain passive support because their muscles are not engaged during the process. Fortunately, this works to reduce a lot of the fatigue that the creature might endure. 

With future studies, Basu said he hopes to further understand how giraffes evolved from small, antelope-like species to the iconic, long-necked ones we're most familiar with, today.

"I'd like to link modern giraffes with fossil specimens to illustrate the process of evolution" Basu concluded. "We hypothesise that the suspensory ligament has allowed giraffes to reach large sizes that they otherwise would not have been able to achieve."

More information regarding the study findings can be found at the Annual Meeting for Society for Experimental Biology 2014 at Manchester University in the UK, from the 1st-4th of July.