There are a few things you can’t miss about a giraffe: that long neck and those extraordinarily long legs.
Those distinctive features help the animal tower above its nearby companions and make grabbing an alluring, sky-high bite to eat relatively easy. But researchers were curious if those long limbs are helpful in daily life.
“Often you hear things in popular science about how animals are ‘perfectly adapted’ for their environment or their lifestyle,” study author Christopher Basu tells Treehugger. Basu was formerly a Ph.D. student at the Royal Veterinary College at the University of London and is now a lecturer in veterinary anatomy at the University of Surrey.
“Giraffes are famed for their ability to feed from high up trees, but we wanted to know whether this came with any sort of penalty, or trade-off. Long legs are good for reaching up high, but do they help or hinder giraffes when they’re getting around?”
Think of a runner who has long legs versus one who has shorter limbs. Long, straight legs in many mammals suggest an advantage linked to speed and better muscle efficiency.
But the extended legs of giraffes may only offer an advantage for tree-top grazing. They might not necessarily turn the animals into athletes.
“Long legs add to giraffes’ overall height. In other long-legged large animals (see ‘horse’), their long straight legs are what is known as a ‘cursorial’ adaptation, meaning well suited to running,” Basu explains. “We wondered if that was really the case in giraffes, which aren’t famed for their athletic performance.”
Estimating Efficiency
For their research, scientists created 3D models of the front legs of giraffes and two related species. They made musculoskeletal models of okapi (Okapia johnstoni), found in Central Africa and known as a “forest giraffe” and to the extinct Sivatherium giganteum, one of the largest giraffes, which lived in the Himalayan foothills more than 2 million years ago.
They used motion capture and other techniques to measure the muscle efficiency of walking giraffes and estimated the efficiency of the two comparable species.
“We filmed walking giraffes at Whipsnade Zoo, U.K., for another study back in 2014, and also measured the forces on the ground as they walked over some force-sensing equipment,” says Basu. “These data, combined with a musculoskeletal model, enabled us to measure muscle efficiency.”
Super Hard to be Athletic
Researchers suspected the long legs weren’t as advantageous as they appeared.
“We have evidence that the long limbs of giraffes incur a penalty,” Basu says. “Because their limbs are so tall, they are particularly sensitive to the forces experienced from gravity, and the forces experienced during walking and running. It means their muscles have to produce large forces to counteract and support the skeleton.”
They thought that giraffes have a low “effective mechanical advantage,” which is the measure of limb efficiency when producing muscle forces. But they were surprised by exactly how low it was. They found it was four times lower than what was expected.
This suggests that the muscles in giraffe legs have to generate high muscle forces for movements that a smaller animal, like a horse, can perform more effectively.
“What was also surprising is that despite the need for large muscle forces, giraffes potentially don’t use much more energy than most other large quadrupeds to walk around,” Basu says. “But it does mean they might find it super hard to do more athletic behaviors.”
The results were published in the journal Proceedings of the National Academy of Sciences.
Learning More About the Giraffe
Researchers say the results are important and pretty interesting.
“It’s really cool because it adds a new element to the popular story of giraffe evolution!” Basu says.
“On one hand, yes, we’re familiar with how leg and neck elongation has helped giraffes, but we now see that this specialization does come with a cost, which in this case is athletic performance."
