Highly specialised ligament structure prevents giraffes from collapsing under the immense pressure of their own weight, according to a new study by the Royal Veterinary College in London.

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

Researchers said that giraffes' bones - equivalent to humans' metatarsal bone (in the foot) and metacarpal bone (in the hand) - are twice as long. A distinct groove in giraffe's leg bones houses a structure called the suspensory ligament. This structure has been identified in other large animals like horses. But, this is the first time that it has been studied in giraffes.

The researchers speculate that this structure might help giraffes' skinny legs to support the animal's body weight.

For the study, the researchers examined limbs from EU zoos that belonged to giraffes, which either died naturally in captivity or had been euthanized. Researchers applied forces of up to 2500 Newtons (250 kilograms) against the bones fixed in a rigid frame. The force was equivalent to the bodyweight supported by each limb.

The researchers found that the limbs remained erect and steady. It didn't crumble down under the force and had the capability of withstanding even greater weight.

Researchers said that since the suspensory ligament is elastic tissue and not muscle, it can't generate force and can only offer passive support. As a result, the giraffes can withstand their weight without involving as much muscle, thereby reducing fatigue.

They also said that this finding can help explain how giraffes transformed from short antelopes to the long-necked animals.

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