Newt Cuts Itself to Use Ribs as "Concealed Weapons"

Scott Norris
for National Geographic News

August 28, 2009

Like the X-men's Wolverine extending his claws, the Spanish ribbed newt slashes through itself with its sharp rib bones to create defensive spines, according to a new study.

Scientists were already aware that the amphibian species responds to threats by thrusting out its rib bones, which then get coated with toxic skin secretions.

But little was known about how the odd adaptation worked.

It had been thought that the newt simply contracted its body, forcing the ends of the ribs out through special openings in the skin.

Now Egon Heiss, of the University of Vienna, and a team of Austrian scientists have shown that the newt is actually rotating its ribs forward until their spear-sharp points pierce through warts in the animal's skin.

"The phenomenon has been known for a long time, but this is the first really detailed study of the rib movements," said Tim Halliday, a biologist at the Open University in London, England, who was not involved in the research.

Quick Healers

Various animals have bony projections that serve as spines. But only the Spanish ribbed newt and a few salamander relatives can brandish their own rib cages like concealed weapons, the researchers say.

(Related: "15-Foot Antarctic 'Salamander' Found; Was Toothy Terror.")

To find out how the newt does it, Heiss's team simulated a predator attack by touching live newts with cotton balls until the amphibians assumed defensive postures.

X-ray and CT scans revealed that rib rotation is key to driving the "spines" outward.

The study didn't find any permanent pores or openings in the animals' skin, which means that the newts are piercing through their own bodies each time the spines deploy.

But the defensive benefits outweigh any risks from the self-inflicted injuries, and the newts quickly recover, the researchers report in a paper published online August 18 in the Journal of Zoology.

"Newts and amphibians in general are known to have an extraordinary ability to repair their skin," Heiss said.

The outer portion of each rib is surrounded by fibers of collagen, a protein used in humans to help heal skin after burns. This suggests its presence on the newt's ribs may accelerate healing, the researchers say.

In addition, a powerful immune system apparently prevents the newt's wounds from becoming infected.

"It seems that, if there is an injury to the newt, it is mild and does not incur a cost," the Open University's Halliday said.

"I have some [of the newts] in a tank in my home office. If I pick them up, I get a mild prick, but the newt seems quite unaffected."

"Chest Puffing"

The new study also offers clues to how the unusual defensive adaptation may have evolved.

The newt's long ribs are attached to its backbone by a flexible two-headed joint that allows the bones to swing forward.

Other salamanders have a similar joint and can expand their rib cages to a lesser degree when threatened. This increases their apparent body size, which is thought to deter predators from attacking.

Such simple "chest puffing" may be what led to the evolution of the Spanish ribbed newt's switchblade-like rib cage, study author Heiss noted.

"If the ribs evolve a longer size, they stretch the skin to the point of piercing it. The rib tips can than be used as weapons."