Fessurum

The fessurum replaced the irondigger. It evolved huge front legs which it "drills" deep down under the surface to find iron. To be able to keep the balance these legs are also used to walk with, and therefore the tail has devolved since it is no longer needed. The fessurum is not very fast, so to defend itself from both creatures and other threats such as falling stones its shell is now much thicker and covers a lot more of its body. The front legs have also got some iron so that they are able to dig easier and it also prevent them from breaking when the fessurum pulls them up out of the ground. The iron and minerals needed for this new shell is easily provided by the very successful method of gaining iron that the fessurum has evolved, but this also means that the fessurum has to spend almost all of its time either feeding or looking for iron.