Spanish ribbed newt

Source: National Geographic News, photo Peter Halasz
The Spanish ribbed newt has a special way of defending itself. When there is danger, its rib bones are pierced through its skin. These are then coated with toxins from the skin and become poisonous spines.
That this is the defensive strategy of the ribbed newt, or Pleurodeles waltl, was already known, but not the exact mechanism behind it. A team of Austrian scientists investigated this. Ribbed newts were poked with cotton balls until they assumed defensive postures. X-rays and CT scans were used to find out the exact mechanism behind this. It a appears to be a rotation of the ribs that makes the bones pierce through the skin. No permanent openings or pores were found in the skin. Every time the ribs pierce through the skin a new hole/wound is made. Despite this injury, the defence mechanism is beneficial to the newt. The animal heals quickly. This is partly due to the fact that the outer portion of each rib is surrounded by collagen fibres. In humans this protein is used to heal skin burns. The animal also has a particularly powerful immune system to prevent infections. Newts and amphibians in general are also known for their extraordinary ability to repair their skin.

The study also offers some clues to how this defence mechanism may have evolved.
The newt's ribs are attached to its backbone by means of a flexible joint that allows the rib bones to swing forward. Other salamanders have similar joints. This joint makes it possible for them to enlarge their chests, which makes them appear bigger and more dangerous. The ribs of the newt may have become larger, which caused them to pierce through its skin when puffing up its chest. The rib tips could then be used as weapons.

This study was published in the Journal of Zoology.
Photo license: Creative Commons Attribution-Share Alike 3.0