and flattened telson of Slimonia (it is also flattened in Salteropterus, but not to the full extent of that of Slimonia) is distinctive and shared only with the pterygotid eurypterids and with the derived hibbertopterid Hibbertopterus and mycteroptid Hastimima, where a flattened telson had convergently evolved. The function of these specialized telsons has historically been controversial and disputed, and whilst study has mainly been focused on telsons within the Pterygotidae, the similarity between the telson of Slimonia and its close relatives should mean that the function would likely have been similar. The pterygotids were hypothesized to have moved by undulating the entire opisthosoma (the large posterior section of the body) by moving the abdominal plates, as such undulations of the opisthosoma and telson would have acted as the propulsive method of the animal, rendering the swimming legs used by other eurypterid groups useless. Fossil evidence contradicts such an hypothesis however, as eurypterid bodies were stiff dorsally (up and down) and preserve no evidence for any sort of tapering or other mechanism that would have increased flexibility. Any flexing of the body would require muscular contractions, but no major apodemes (internal ridges of the exoskeleton that supports muscular attachments) or any muscle scars indicative of large opisthosomal muscles have been found. Instead, propulsion was likely generated by the sixth pair of appendages, the swimming legs used by other eurypterine eurypterids. Whilst stiff dorsally, fossil evidence suggests that Slimonia was very flexible laterally (side to side). A specimen of Slimonia acuminata from the Patrick Burn Formation of Scotland preserves a complete and articulated series of telsonal, postabdominal and preabdominal segments. In the specimen, the "tail" is bent to a considerable degree previously unseen in any eurypterid. Capable of bending its tail from side to side, it has been theorised that the tail may have been used as a weapon. The telson spine, serrated along the sides and exceeding the flattened telson in length, ends in a sharp tip and would likely have been capable of piercing prey. In pterygotids, it is likely that the cheliceral claws came to replace telson spikes as weaponry as the telson spikes of that family are relatively shorter than those of the Slimonidae. However, this theory has been proven to be erroneous as the fossil specimen in question was a molt, rather than an actual carcass, and did show apparent signs of disarticulation. The telson of Salteropterus