The Eternal Arms Race Between Weapon and Armor
This world has a race of giant crabs who have developed armor sufficiently strong that the top predator's teeth can't puncture the armor. In response, the top predator has taken the next evolutionary step of developing specialized hammer shaped teeth and extremely fast closing jaws. The jaws close fast enough to create shockwaves in the crustacean's armor that generate high speed fragments that bounce around for a bit. (In modern tank armor, these high speed fragments are called spall). Spall damage to the crab's muscles and organs slow it down enough for the predator to finally kill the crab.
This is somehow familiar...
We've seen this kind of evolution in the development of HESH ammo in WWII by the British and the use of warhammers against late medieval armor plate. If puncture attacks don't work, go for percussion. For human carried plate armor, there was no counter as firearms made armor obsolete. In response to HESH, tanks and other armored vehicles acquired spaced armor and spall liners.
How likely is it that these giant crustaceans would develop the equivalent of spall liners inside their shells to deal with the spall generated by the predator's bite? If they don't develop spall liners, what would be the simplest and cheapest evolutionary change combat the predator's bite?
Out of Scope:
- We are ignoring the scaling problems of getting giant crustaceans. There are lots of reasons why we don't see these on earth but we are ignoring those problems. These crustaceans just get big.
- How the predator bites so quickly. It just does.
- None of these creators are designed, nor can the changes made to them be designed. Whatever countermeasures the crab develops must work and provide benefit at all times during the evolutionary process.