Kangaroos Walk on Their Tails
A pair of Common reef cuttlefish (Sepia latimanus) hovers above a patch of hard coral located on the Far Northern part of the Great Barrier Reef. With the ocean warming, rising, and becoming more acidic, coupled with land runoff, marine pollution and coastal development -- life in Australia's Great Barrier Reef is threatened from all sides and may be placed on the "in danger" designation for UNESCO World Heritage Sites. Can Australia meet the challenge to do a better job of protection by 2014? Here's some photos of what's at risk.
Clownfish protect their eggs hidden in a sea anemone on the Great Barrier Reef.
The most-loved Heart Reef among the Whitsunday Islands in the Great Barrier Reef is part of the protected off-limits areas to SCUBA divers and snorklers.
A flying gurnard (Dactyloptena orientalis), spreads out large pectorals to scare away enemies on the Great Barrier Reef, Australia.
The poisonous blue-ringed octopus (Hapalochlaena lunulata) stalks prey among the coral.
Jeffrey L. Rotman/Corbis
The size isn't intimidating, but the deadly poison is; divers wear gloves to hold the blue-ringed octopus.
A black-blotched moray eel at home in the Great Barrier Reef off the coast of Australia.
The polyps on this stalk of Acropora echinata, a type of Staghorn coral, show vividly colored tips.
Many reefs around the world are threatened by bleaching, as sea temperatures become too warm and stress the corals. The high temperatures kill the colorful polyps, and leave a reef cemetery of coral skeletons.
Staghorn Coral release eggs and sperm in a mass spawning event on the Great Barrier Reef.
The head of a whale shark (Rhincodon typus), near Ningaloo Reef in West Australia - Indian Ocean. Whale sharks feed on the eggs and sperm released from coral during massive spawning events a few days after the full moon between October and December.
What goes in must come out. A sea cucumber (Thelnota ananas) leaves a trail of waste as it processes its food.
The head of an Ocellated Epaulette shark (Hemiscyllium ocellatum), in the Great Barrier Reef, Australia.
Sea level rise poses a real threat to many parts of Australia. Already increased coastal erosion as a result of sea level rise is evident, as here where trees have been undercut and toppled by erosion on Green Island off Cairns in Queensland, Australia.
Kangaroos use their tail as an extra leg when they walk, according to new research.
The study, reported in Royal Society Biology Letters, found that the animals use their tail more than their forelimbs when they walk.
The findings provide new insights into kangaroo locomotion, and could also have applications in advanced robotics.
Professor Terry Dawson of the University of New South Wales and colleagues have previously shown that during hopping, the kangaroo tail acts as a counterbalance, and as a spring to store up energy for the next bounce.
"Hopping is an exaggerated gallop, enabling the kangaroo to make longer steps," says Dawson.
In this study the researchers were interested in working out how kangaroos walk.
When kangaroos walk they had been observed to use what is known as a "pentapedal tail walk", says Dawson.
This unusual gait means the animal effectively always has three points on the ground, with one of them always being their tail, and the other two being either their two hind legs, or their two forelimbs.
However the energetics of pentapedal walking indicated that it was less energy efficient than walking on four legs, says Dawson.
"This was always a puzzle," he says.
While previous literature suggested kangaroos used their tail as a "strut to hold the body in place while they move the back legs forward," Dawson suspected something else was happening.
"It appeared to me they were using the tail for propulsion when walking," he says.
To test this hypothesis, Dawson and colleagues trained one male and four female red kangaroos (Macropus rufus) to walk over a force-measuring platform that monitored the energy used by different parts of the kangaroo as it walked.
The researchers found that kangaroos walk by using the tail to lift both hind legs and the body's centre of gravity forward, while the forelimbs were used as struts and didn't provide any of the propulsion.
The tests showed there was far more propulsion energy provided by the tail than scientists had thought.
The kangaroo's tail provides as much propulsive energy as one of the hind legs, between a quarter and a third of the full propulsion needed to move the animal forward, they found.
"We expected this is because the muscles in the tail and hind legs are highly aerobic, with a lot of mitochondria in them doing a lot of work," says Dawson.
Mitochondria act as a cell's power house, providing energy.
"The muscle structure of the front legs have little mitochondria and they're not organised for propulsion, so instead of the tail being the strut, the front legs were filling that role," says Dawson.
"I can now understand where that energy goes and why if they're going to walk more than 5 metres they get up and hop instead."
Dawson says the team is interested in mechanical analogues to walking and locomotion.
"There's interest in the robotic side of things and how other forms of locomotion can work," says Dawson.
"You can locomote just using your legs, but there are other options for stability and it's interesting from that point of view."