Slimonia
Slimonia | |
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Fossil of S. acuminata housed at the Senckenberg Museum of Frankfurt | |
Scientific classification | |
Domain: | Eukaryota |
Kingdom: | Animalia |
Phylum: | Arthropoda |
Subphylum: | Chelicerata |
Order: | †Eurypterida |
Superfamily: | †Pterygotioidea |
Family: | †Slimonidae |
Genus: | †Slimonia Page, 1856 |
Type species | |
†Slimonia acuminata Salter, 1856
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Species | |
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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 (7.9 in) in length. Only S. acuminata was larger, with the largest specimens measuring 100 centimetres (39 in) in length. Though this is large for a predatory arthropod, Slimonia would be exceeded in length by later and more
Description
Slimonia is in many ways similar to the more
Slimonia can be distinguished from other members of its family, the
History of research
The
In 1899, an additional species, S. dubia, would be referred to the genus. This species was recovered from slightly earlier deposits (Llandovery age) in the Pentland Hills of Scotland and could be distinguished from S. acuminata by the more elongated telson (also not as broad in the parts furthest back), thinner telson spike and a slightly different, tapering, body shape that tapers evenly the whole way instead of suddenly narrowing near the seventh segment as in S. acuminata.[8][9] The type specimen of S. dubia is a badly preserved carapace, with fragments of various degrees of completion of the first eleven segments found associated. Despite its fragmentary nature, the quadrangular (square) shape of the carapace and the eyes placed at its corners allowed zoologist and paleontologist Malcolm Laurie to place it within Slimonia when describing it in 1899.[8] The size of the carapace suggests that the species would have grown to 12 cm (5 in) in length.[3]
Another species, S. stylops, was first considered a species of Pterygotus when described by John William Salter in 1859, and the highly fragmentary nature of the known fossils make a precise identification difficult and problematic. Only one specimen, the anterior part of a carapace with the compound eyes placed on the margin, is known and though it does resemble Slimonia, it could also potentially be referred to Hughmilleria or even represent the carapace of Salteropterus abbreviatus (a closely related slimonid eurypterid known only from the telson and metastoma, a large plate part of the abdomen).[10] The fossils were recovered from deposits of Pridoli (Late Silurian) age in Herefordshire, England and suggest that the species grew to 12 cm (5 in) in length.[3] Due to its problematic nature, S. stylops is seen as a nomen dubium by modern researchers.[11]
In 1973, another species of Slimonia was named by Kjellesvig-Waering based on one single fossil recovered by Eduardo Rodriguez from the
Classification
Slimonia is one of the most closely related genera to the pterygotid family and the Slimonidae is often interpreted as a sister-taxon to the Pterygotidae. The other Pterygotioid family, the Hughmilleriidae, has also been interpreted as the most closely related sister-taxon to the pterygotids. The discovery of Ciurcopterus, the most primitive known pterygotid, and studies revealing that Ciurcopterus combines features of Slimonia (the appendages are particularly similar) and of more derived pterygotids, revealed that the Slimonidae is more closely related to the Pterygotidae than the Hughmilleriidae is.[14]
The cladogram below is simplified from a study by O. Erik Tetlie (2007),[15] and showcases the position of Slimonia relative to the rest of the Eurypterina suborder of eurypterids, with the Stylonurina suborder as an outgroup.
Eurypterida
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Paleobiology
In 2017, W. Scott Persons IV and John Acorn reported finding an S. acuminata specimen, MB.A 863, in the Patrick Burn Formation of Scotland, dated to the Telychian, around 430 million years ago. The specimen was a complete and articulated series of telsonal, postabdominal and preabdominal segments, and it showed a very strong lateral curvature in the postabdomen. Persons and Acorn admitted that it might have experienced some disarticulation postmortem or could represent a partial molt (exuviae), but concluded that since there was no apparent disarticulation in the metasoma, it was likely that the articulation seen in the postabdominal segments (which is also seen in some other eurypterid fossils, such as of Eurypterus and Alkenopterus) would have been possible in life.[2]
Biomechanical studies on the telsons and postabdominal segments of eurypterids closely related to Slimonia, particularly those of the family Pterygotidae, had revealed that the body was very stiff, and that the flattened telson would likely have served 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 the telson would have served a propulsive function.[1] Whilst the postabdomen of Slimonia was likely similarly stiff and inflexible dorsally (up and down), Persons and Acorn claimed that their specimen suggested that it was highly flexible laterally (side to side). As such, they 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 they proposed that it could have been capable of piercing prey.[2][16]
However, the Persons and Acorn theory was challenged in 2018 by James Lamsdell, David Marshall, and Derek Briggs. Even though the Persons and Acorn study claimed that the fossil didn't show any signs of disarticulation, Lamsdell, Marshall, and Briggs showed this is likely not true. They argued that both tergite 8 and 10 clearly overlapped the other tergites in an unnatural way. Furthermore, they noted that the specimen was definitely a molt rather than a carcass, and argued that this meant that the pose the fossil was in did not represent a possible life position. They further argued that since the telson of Slimonia also possessed a keel, this would have created significant drag on it while Slimonia was trying to laterally sweep the telson to stab its prey. Lastly, they argued that the serrations on the telson would most likely be attachment points for setae that would have aided the animal in sensing the water flow to make steering much easier.[17]
Paleoecology
Fossils of Slimonia have been recovered in deposits home to diverse eurypterid faunas. Telychian deposits in the Pentland Hills, where remains of S. dubia have been found, preserve fossils of a large amount of other eurypterids, including Drepanopterus pentlandicus, Laurieipterus elegans, Parastylonurus ornatus, Hardieopterus macrophthalmus, Carcinosoma scoticus, Stoermeropterus conicus and Pentlandopterus minor. Also preserved are fossils of orthocerids, such as Geisonoceras maclareni.[8] Similar levels of eurypterid diversity are also observed in fossil deposits where other species of Slimonia have been found. S. acuminata has been found associated with Nanahughmilleria lanceolata, Hardieopterus lanarkensis, Eusarcana obesus, Parastylonurus sigmoidalis, Carcinosoma scorpionis and Erettopterus bilobus[19][20] and S. stylops have been found associated with Nanahughmilleria pygmaea, Eusarcana salteri, Hardieopterus megalops, Erettopterus brodiei, E. gigas, Hughmilleria banksi, Eurypterus cephalaspis and Pterygotus ludensis.[21]
The living environment of the pterygotids differed from genus to genus, with some (such as
Like many eurypterid species, Slimonia acuminata requires a modern re-description to properly establish defining traits and characteristics. Some traits that appear to be unique to S. acuminata have been described based on specimens housed at the Doncaster Museum and Art Gallery, including rows of pustules (bulges) along the marginal rim of the body and appendages. In some arthropods, pustules serve as attachment points of setae (bristle- or hair-like structures with sensory functions). Similar pustule rows have been discovered in the other eurypterid Drepanopterus abonensis, a sweep-feeder that used the marginal rim to search the substrate of its living environment for prey. If the pustules of S. acuminata had setae, these pustules may have functioned as tactile and sensory organs used for locating and identifying prey, together with the pedipalps (the gracile second pair of appendages, behind the chelicerae).[25]
See also
References
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- ^ a b c Dunlop, J. A., Penney, D. & Jekel, D. 2015. A summary list of fossil spiders and their relatives. In World Spider Catalog. Natural History Museum Bern, online at http://wsc.nmbe.ch , version 16.0 http://www.wsc.nmbe.ch/resources/fossils/Fossils16.0.pdf (PDF).
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- ^ "A killer tail spine likely helped this ancient sea scorpion subdue its prey". Science | AAAS. 2017-04-17. Retrieved 2018-03-18.
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- ^ "Eurypterid-Associated Biota of the Patrick Burn Fm., Lesmahagow (Siltstones) (Silurian to of the United Kingdom) - Fossilworks". fossilworks.org. Retrieved 17 December 2021.
- ^ "Eurypterid-Associated Biota of the Kip Burn Fm., Lesmahagow, Scotland (Silurian to of the United Kingdom) - Fossilworks". fossilworks.org. Retrieved 17 December 2021.
- ^ "Eurypterid-Associated Biota, Platyschisma Beds, Downton Castle Sst., Herefordsh. (Silurian of the United Kingdom) - Fossilworks". fossilworks.org. Retrieved 17 December 2021.
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