Trilobites exhibiting injuries are ideal palaeontological archives for Palaeozoic predator-prey interactions. However, the current methods for diagnosing trilobite injuries primarily depend on the various morphological features at the edges of the injured exoskeleton, without evaluating the process and timing of morphological changes. Here we performed an amputation experiment utilizing the extant horseshoe crab as a proxy of trilobites to study the morphological changes after injury. The results show that: the wound closure was accomplished by forming hemolymph clotting on the wound surface in a short time. And then, a thin cuticle layer was growing on the inner side of wounded exoskeleton, with the retention of a sharp outline of the wound. Particularly, the newly-formed exoskeleton only regenerates and modifies the shape of the wound subsequent to moulting. After rechecking 409 abnormal trilobites documented in the published literature, we recognized that the injuries with sharp exoskeleton edge are very rare in the fossil record, and 95% of injured trilobites with clearly identifiable scars had undergone at least one subsequent ecdysis. This indicates that the majority of the injuries were not identified, as the sharp wounds were indistinguishable from post-mortem breakage. These unidentified injuries may encompass successful predation events, lethal injuries, and damage incurred during the adult stage, none of which exhibit signs of moulting. Although we are currently unable to deal with this recognition bias, through injury experiments on living arthropods, our understanding of the damage types and repair processes of trilobites will be further enriched.