The kangaroo's tail propels and powers pentapedal locomotion



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The paper will remain under embargo until 00.01 BST Wednesday 2 July 2014.

Contact Information


Primary: Max Donelan, Professor, Simon Fraser University, mdonelan@sfu.ca (website)
Secondary: Shawn O'Connor, Postdoctoral Researcher, UCSD, s2oconnor@ucsd.edu (website)
Co-author: Rodger Kram, Professor, University of Colorado - Boulder, Rodger.Kram@colorado.edu (website)
Co-author & Australian Kangaroo Expert: Terry Dawson, Professor Emeritus, UNSW, t.dawson@unsw.edu.au

Summary


When moving slowly, kangaroos use a “pentapedal” gait, planting their tail on the ground in combination with their front and hind legs. We measured the forces the tail exerts on the ground, and calculated the mechanical power it generates. We found that the tail is responsible for more propulsive force than the front and hind legs combined. It also generates almost exclusively positive mechanical power, performing as much mass-specific mechanical work as a human leg when walking at the same speed. Kangaroos use their muscular tail to propel and power their motion just like a leg.

Paper Download


O'Connor SM, Dawson TJ, Kram R, Donelan JM. 2014 The kangaroo's tail propels and powers pentapedal locomotion. Biology Letters. 20140381. http://dx.doi.org/10.1098/rsbl.2014.0381

FAQs


What were your primary findings, and did you find them surprising?
“Our main finding is that when kangaroos are walking pentapedally, which they spend more time doing than hopping, they use their tail just like a leg. That is, they use it to support, propel and power their motion. In fact, they performed as much mechanical work with their tail as we do with one of our legs. This surprised us because no other animal uses their tail in this manner and their tails are very different anatomically from a leg. During pentapedal gait, the kangaroo's more than 20 tail vertebrae take on the roles of our feet, calf and thigh bones.” – Dr. Shawn O'Connor 

What led you to study kangaroos?
“One of the central findings of our human walking research is that it is very important to time the push-off of your back leg to make walking less effortful. People recovering from strokes or spinal cord injury can’t do this as well because their legs are partially immobilized, making walking more effortful for them. What does this have to do with kangaroos? Well, when kangaroos move slowly, they walk “pentapedally” planting their tail on the ground in sequence with their front and hind legs. But, their front legs are very short and can’t be used to push off. The timing and position of the tail, on the other hand, is perfect. So, we wondered if they are able to use their tail just like a leg to push off and power their walking? We found that they indeed do. In fact, they do as much work with their tail as we do with one of our legs. This is quite remarkable given that the tail is anatomically quite different, being composed of more than 20 vertebrae rather than a few leg bones, and evolved to swing on branches rather than push on the ground. Animals have discovered many uses for their tails, but as far as we know, this is the first use of one as a leg.” – Dr. Max Donelan

 “As an aside, part of my desire to study kangaroos stemmed from my experience as a graduate student in a biology department. My fellow students were off studying wild animals in exotic places like Tahiti and Borneo while I chose to study humans walking over force plates in a basement lab. I eventually got a clue and devised a plan to test some of my ideas in a wild animal in an exotic place—kangaroos in Australia. Apparently I don’t catch on that fast as rather than end up on a walkabout in the outback, I found myself stuck in the lab using force plates again, albeit with very cool kangaroos.” – Dr. Max Donelan

What does this research tell us about locomotion in general?
“Beyond a better understanding of how kangaroos move, this research tells us about how important it is to push-off and help redirect the body’s velocity when transitioning from one stance limb to the next. We know healthy humans do this nearly perfectly. We know that people with gait disorders and disabilities don’t do it as well which increases the effort required for them to walk. We have built prosthetics and exoskeletons that help improve their ability to do so and make walking easier. And now we know that it is important enough that kangaroos have harnessed a limb originally evolved for swinging from trees to serve this role as a functional fifth leg.” – Dr. Max Donelan

How does this fit with your other research interests?
Please see above. But also: “We are interesting in the fundamental principles underlying biological movement. One way we study these principles is to examine one organism, humans, in greater and greater detail. But another approach, and the one we use here, is to study the diversity of movement. Unusual gaits by unusual animals, such as pentapedal walking by kangaroos, provide insight into the breadth of solutions available to the same biomechanical problem of getting from one place to another.” – Dr. Max Donelan

When and where was this carried out?
“We made these measurements in Terry Dawson’s lab at the University of New South Wales in Sydney Australia. The original measurements were made in 2001 but we were just recently able to analyze them properly due to innovations by my collaborator, Dr. Shawn O’Connor.” – Dr. Max Donelan 

What do you find fascinating about kangaroo locomotion, both hopping and grazing?
“What’s not to find fascinating about kangaroos? Their hopping is incredibly fast, powerful, and efficient. Their walking, on the other hand, is as awkward as their hopping is graceful, but underlying the walking gait is this entirely new use for a tail. Biomechanically, it is all fascinating.” – Dr. Max Donelan

Illustrations


Illustration of the kangaroo's fore limb, hind limb, and tail skeletal structures.

Download: pdf version; high-res jpg version (1718 x 1125 pixels)

Credit: Heather More, Simon Fraser University
  
https://drive.google.com/file/d/0B6uQT1aasa3nQUZsZ1ppM3hfSzQ/edit?usp=sharing

Illustration of the kangaroo's fore limb, hind limb, and tail skeletal structures with corresponding photo of a red kangaroo

Download: pdf version; high-res jpg version (3500 x 1125 pixels)
 
Credit: Heather More, Simon Fraser University

https://drive.google.com/file/d/0B6uQT1aasa3nVUdudnpfdnlMaXc/edit?usp=sharing

Illustration of a full stride cycle during pentapedal locomotion

Download: pdf version; high-res jpg version (1304 x 94 pixels)
 
Credit: Shawn O'Connor, Simon Fraser University



https://sites.google.com/a/locomotionlab.com/pentapedal-locomotion/home/Roo%20Outline%20Series%20credit%20Shawn%20OConnor.jpg?attredirects=0

Figure 1 from Biology Letters research article depicting stills of pentapedal locomotion in the red kangaroo

Download: pdf version; high-res jpg version (1905 x 904 pixels)
 
Credit: SFU Locomotion Lab

https://drive.google.com/file/d/0B6uQT1aasa3nOXlmcDNVdlBkbTg/edit?usp=sharing

Figure 2 from Biology Letters research article depicting force and power generation by the limbs during pentapedal locomotion

Download: pdf version; high-res jpg version (1940 x 1123 pixels)
 
Credit: SFU Locomotion Lab

https://drive.google.com/file/d/0B6uQT1aasa3ndkVOOE9KYUFjTEU/edit?usp=sharing

Photos


Photograph of a red kangaroo standing at the Fowlers Gap Arid Zone Research Station

Download: high-res jpg version (4184 x 2583 pixels)
 
Credit: Catharina Vendl, Fowlers Gap
https://drive.google.com/file/d/0B6uQT1aasa3nRkc0NFNWTGFFRW8/edit?usp=sharing
Photograph of a red kangaroo walking at the Fowlers Gap Arid Zone Research Station

Download: high-res jpg version (3240 x 2000 pixels)

Credit: Catharina Vendl, Fowlers Gap
https://drive.google.com/file/d/0B6uQT1aasa3nQldGbUo2YVQxaEU/edit?usp=sharing
Photograph of a red kangaroo walking at the Fowlers Gap Arid Zone Research Station

Download: high-res jpg version (3059 x 1888 pixels)
 
Credit: Catharina Vendl, Fowlers Gap
https://drive.google.com/file/d/0B6uQT1aasa3nanNXcVI3UW93QUE/edit?usp=sharing
Photograph of a red kangaroo walking at the Fowlers Gap Arid Zone Research Station

Download: high-res jpg version (3052 x 1884 pixels)
 
Credit: Catharina Vendl, Fowlers Gap
https://drive.google.com/file/d/0B6uQT1aasa3nd09wc2hMTXlxNFk/edit?usp=sharing
Photograph of a red kangaroo walking at the Fowlers Gap Arid Zone Research Station

Download: high-res jpg version (2991 x 1846 pixels)

Credit: Catharina Vendl, Fowlers Gap
https://drive.google.com/file/d/0B6uQT1aasa3nOFdsX00xdW91Zjg/edit?usp=sharing

Videos


Video explaining the pentapedal walking gait

Download: H.264  low-res (4MB: 
480 x 352 pixels)
                             medium-res (23MB: 640 x 480 pixels)
                             
high-res (92MB: 984 x 722 pixels)

Credit: SFU Locomotion Lab
 
Video of a red kangaroo walking at the Fowlers Gap Arid Zone Research Station

Download: H.264 high-res (3MB: 960 x 540 pixels)

Credit: Catharina Vendl, Fowlers Gap