pentapedal

In the latest (7/5/14) New Scientist, a “60 seconds” (ultra-brief) feature “Bouncing on five legs”:

Kangaroos have five “legs”, making them the first known pentapedal animals. A study of kangaroo motion suggests their tails aren’t simply a crutch but actively move them forward, producing as much propulsive force as all four limbs combined (Biology Letters, DOI: 10.1098/rsbl.2014.0381).

What about starfish? Aren’t they pentapedal animals? What about primates that use their tails (in addition to their hands and legs) to propel themselves?

Well, it depends on what you mean by animal and what you mean by leg. Starfish are customarily said to have five arms, and primates to have only two legs (but four limbs, plus, for some, a tail that can function rather like another limb).

The abstract from the Royal Society site, which refers to a pentapedal gait, and not to a pentapedal animal:

When moving slowly, kangaroos plant their tail on the ground in sequence with their front and hind legs. To determine the tail’s role in this ‘pentapedal’ gait, 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 as much propulsive force as the front and hind legs combined. It also generates almost exclusively positive mechanical power, performing as much mass-specific mechanical work as does a human leg during walking at the same speed. Kangaroos use their muscular tail to support, propel and power their pentapedal gait just like a leg.

Similar caution can be seen on other sites, for instance on the terminology page of the Back to Nature Wildlife Shelter site:

Pentapedal Movement – using forelimbs, hindlimbs and tail to move around (pent means five)

This version uses limbs rather than legs, and might well take in some primates as well as kangaroos.

None of this detracts from the wonder of the kangaroo’s tail.

One Response to “pentapedal”

  1. arnold zwicky Says:

    From Éamonn McManus on Facebook:

    Dr Pedant thinks it should be pentapodal, and indeed the Goog finds existing uses of that, as well as a Harry Potter creature called a Pentapod.

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