How Giraffes Don't Collapse Under Their Own Immense Weight: Specialized Ligament Structure

With their long necks and legs, giraffes look as if they might have problems staying upright with their unique physiology. Now, scientists have found out exactly how these animals remain standing. They've identified a specialized ligament structure that is thought to prevent giraffes' legs from collapsing under their own immense weight.

"Giraffes are heavy animals (around 1000 kg), but have unusually skinny limb bones for an animal of this size," said Christ Basu, the lead investigator, in a news release. "This means their leg bones are under high levels of mechanical stress."

In giraffes, the equivalents to our metatarsal bone and metacarpal bone, which are located in the foot and hand respectively, are extremely elongated. In fact, they account for roughly half of the length of the leg. In addition, a distinct groove runs along the length of these bones, housing a structure called the suspensory ligament. This structure can also be found in other large animals, such as horses. Yet this is the first time it's been studied in giraffes

In order to see whether this ligament might be the reason why giraffes can support their own immense weight, the scientists looked at donated limbs from zoos. The scientists then fixed these limbs in a rigid frame and the scientists, using a hydraulic press, applied forces of up to 2500 Newtons to simulate bodyweight.

So what did they find? It turns out that the limbs remained upright and stable without any additional support. In fact, they could even withstand greater loads. The ligament seemed to be offering passive support, which means that giraffes can support their weight without actively engaging as much muscle; this, in turn, helps reduce fatigue.

"We hypothesize that the suspensory ligament has allowed giraffes to reach large sizes that they otherwise would not have been able to achieve," said Basu.