page_title: Slimonia
section_title: Paleobiology
hierarchical_section_title: Slimonia / Paleobiology
caption_attribution_description: English: Holotype (and only known specimen) of the eurypterid species Slimonia boliviana, a telson. Based on Kjellesvig-Waering, 1973
context_page_description: Slimonia is a genus of eurypterid, an extinct group of aquatic arthropods. Fossils of Slimonia have been discovered in deposits of Silurian age in South America and Europe. Classified as part of the family Slimonidae alongside the related Salteropterus, the genus contains three valid species, S. acuminata from Lesmahagow, Scotland, S. boliviana from Cochabamba, Bolivia and S. dubia from the Pentland Hills of Scotland and one dubious species, S. stylops, from Herefordshire, England. The generic name is derived from and honors Robert Slimon, a fossil collector and surgeon from Lesmahagow.
  Out of the four described species of Slimonia, three measured below or up to 20 centimetres in length. Only S. acuminata was larger, with the largest specimens measuring 100 centimetres in length. Though this is large for a predatory arthropod, Slimonia would be exceeded in length by later and more derived members of the closely related pterygotid family of eurypterids, which would become the largest known arthropods to ever live.
context_section_description: The specimen MB.A 863, a S. acuminata discovered in the Patrick Burn Formation (dated to the Telychian, around 430 million years ago) of Scotland, preserves a complete and atriculated series of telsonal, postabdominal and preabdominal segments. The specimen might have experienced some disarticulation postmortem (or could represent a partial exuviae), but as there is no apparent disarticulation in the metasoma, it is likely that the articulation seen in the postabdominal segments would have been possible in life (which is also seen in some other eurypterid fossils, such as of Eurypterus and Alkenopterus).
  Biomechanical studies on the telsons and postabdominal segments of closely related eurypterids, particularly those of the family Pterygotidae, has revealed that the body was very stiff, and that the flattened telson would likely have served a function as a rudder that would have allowed the animals to be agile and capable of quick turns when chasing after prey, contradicting previous hypotheses that they would have served a propulsive function. Whilst the postabdomen of Slimonia was likely similarly stiff and inflexible dorsally (up and down), the study of the specimen suggests that it was highly flexible laterally (side to side). As such, 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 it was proposed that it could have been capable of piercing prey.
  However, this particularly theory was later criticized and disproved. Even though the original study claimed that the fossil didn't show any signs of disarticulation, this is likely not true. It can be clearly seen that both tergite 8 and 10 overlap the other tergites in an unnatural way. Furthermore, it was noted that the specimen was not a carcass, rather a molt. This would mean that the pose the fossil was in does not represent a possible life position. The telson of Slimonia also possesses a keel, which would have created significant drag while trying to stab its prey. Lastly, the serrations on the telson would most likely be attachment points for setae and would have aided the animal in sensing the water flow. This made steering much more easier.
  Visual acuity, the clarity of vision, can be determined in arthropods by determining number of lenses in their compound eyes and the interommatidial angle (shortened as IOA and referring to the angle between the optical axes of the adjacent lenses). The IOA is especially important as it can be used to distinguish different ecological roles in arthropods, being low in modern active arthropod predators. Slimonia was very similar to the basal pterygotid Erettopterus in terms of visual acuity, with the number of lenses being comparable to those of Pterygotus and Jaekelopterus and possessing an IOA between 2 and 3 (which is higher than the IOA of Pterygotus and Jaekelopterus, suggesting that the visual acuity of Slimonia was good, but not as good as in the derived pterygotids).
caption: Drawing of the holotype of S. boliviana, a telson.
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