Megarachne
Megarachne | |
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Cast of the holotype specimen of Megarachne exhibited at Royal Ontario Museum | |
Scientific classification | |
Domain: | Eukaryota |
Kingdom: | Animalia |
Phylum: | Arthropoda |
Subphylum: | Chelicerata |
Order: | †Eurypterida |
Superfamily: | †Mycteropoidea |
Family: | †Mycteroptidae |
Genus: | †Megarachne Hünicken, 1980 |
Species: | †M. servinei
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Binomial name | |
†Megarachne servinei Hünicken, 1980
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Megarachne is a
With a body length of 54 cm (21 in), Megarachne was a medium-sized eurypterid. If the original identification as a spider had been correct, Megarachne would have been the largest known spider to have ever lived. Eurypterids such as Megarachne are often called "sea scorpions", but the strata in which Megarachne has been found indicates that it dwelled in freshwater and not in marine environments.
Megarachne was similar to other eurypterids within the Mycteropoidea, a rare group known primarily from South Africa and Scotland. The mycteropoids had evolved a specialized method of feeding referred to as sweep-feeding. This involved raking through the substrate of riverbeds in order to capture and eat smaller invertebrates. Despite only two specimens having been recovered, Megarachne represents the most complete eurypterid discovered in Carboniferous deposits in South America so far. Due to their fragmentary fossil record and similarities between the genera, some researchers have hypothesized that Megarachne and two other members of its family, Mycterops and Woodwardopterus, represent different developmental stages of a single genus.
Description
Known fossils of Megarachne indicate a body length of 54 cm (21 in). While large for an arthropod, Megarachne was dwarfed by other eurypterids, even relatively close relatives such as Hibbertopterus which could reach lengths exceeding 1.5 m (59 in).[1] Though originally described as a giant spider, a multitude of features support the classification of Megarachne as a eurypterid. Among them, the raised lunules (the vaguely moon-shaped ornamentation, similar to scales) and the cuticular sculpture of the mucrones (a dividing ridge continuing uninterrupted throughout the carapace, the part of the exoskeleton which covers the head) are especially important since these features are characteristic of eurypterids.[2]
Megarachne possessed blade-like structures on its appendages (limbs) which would have allowed it to engage in a feeding method known as sweep-feeding, raking through the soft sediment of
Megarachne was very similar to other
History of research
Megarachne servinei was originally described in 1980 by the Argentine
Hünicken wrongly identified the specimen as a
With an estimated length of 33.9 cm (13.3 in) based on the assumption that the fossil was of a spider, and a legspan estimated to be 50 centimetres (20 in), Megarachne servinei would have been the largest spider to have ever existed, exceeding the goliath birdeater (Theraphosa blondi) which has a maximum legspan of around 30 cm (12 in). Because of its status as the "largest spider to have ever lived", Megarachne quickly became popular. Based on Hünicken's detailed description of the fossil specimen and various other illustrations and reconstructions made by him, reconstructions of Megarachne as a giant spider were set up in museums around the world.[8][6]
The identification of the specimen as a spider was doubted by some
In 2005, a second, more complete specimen consisting of a part and counterpart (the matching halves of a
Classification
Megarachne was part of the
Fossilized remains of the second tergite of the mycteroptid Woodwardopterus were compared to the fossil remains of Megarachne by Selden and colleagues (2005), which revealed that they were virtually identical, including features previously not noted in Woodwardopterus, such as radiating lines covering the tergite. It was concluded that Megarachne and Woodwardopterus were part of the same family by Selden and colleagues (2005), with two primary differences; the tergites and the mucrones on the carapace are more sparsely packed in Megarachne and the protrusion of the anteroedian (i.e. before the middle) carapace, seen prominently in Megarachne, does not occur in Woodwardopterus.[2]
It has been suggested that three of the four
The cladogram below is adapted from Lamsdell and colleagues (2010)[3] and shows the relationship of Megarachne within the suborder Stylonurina.
Stylonurina |
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Paleoecology
Both known specimens of Megarachne have been recovered from the
During Megarachne's time, Argentina and the rest of South America was part of the ancient supercontinent
In comparison to the comparatively warm climate of the earlier parts of the Carboniferous, the Late Carboniferous was relatively cold globally. This climate change likely occurred during the Middle Carboniferous due to falling CO2 levels in the atmosphere and high oxygen levels. The
In popular culture
During the production of the 2005 British documentary Walking with Monsters, Megarachne was slated to appear as a giant tarantula-like spider hunting the cat-sized reptile Petrolacosaurus in the segment detailing the Carboniferous, with the reconstruction closely following what was thought to be known of the genus at the time the series began production. The actual identity of the genus, as a eurypterid, was only discovered well into production and by then it was far too late to update the reconstructions. The scenes were left in, but the giant spider was renamed as an unspecified species belonging to the primitive spider suborder Mesothelae, a suborder that actually exists but with genera much smaller than, and looking considerably different from, the spider featured in the program.[6]
References
- .
- ^ PMID 17148124.
- ^ S2CID 85398946.
- ^ Størmer, Leif (1955). "Merostomata". Treatise on Invertebrate Paleontology, Part P Arthropoda 2, Chelicerata. p. 39.
- ^ PMID 17148124.
- ^ PMID 17148124. Retrieved 16 November 2012.
- ^ PMID 17148124.
- ^ PMID 17148124.
- S2CID 41619505.
- ISSN 0024-4082.
- ^ Dunlop, J. A., Penney, D. & Jekel, D. 2018. A summary list of fossil spiders and their relatives. In World Spider Catalog. Natural History Museum Bern, p. 19
- ^ "Bajo de Veliz (CORD collection), Carboniferous of Argentina". Fossilworks. Retrieved 17 December 2021.
- ^ .
- .
External links
- Media related to Megarachne at Wikimedia Commons
- Data related to Megarachne at Wikispecies