Squaloraja (Latin for "shark-skate") is an extinct genus of ray-like marine chimaeriform fish from the Early Jurassic of Europe.[1]
| Squaloraja Temporal range: Early Jurassic,
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| S. polyspondyla fossil | |
Scientific classification 
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| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Chondrichthyes |
| Subclass: | Holocephali |
| Order: | Chimaeriformes |
| Suborder: | †Squalorajoidei |
| Family: | †Squalorajidae Woodward, 1886 |
| Genus: | †Squaloraja Riley, 1833 |
| Species: | †S. polyspondyla
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| Binomial name | |
| †Squaloraja polyspondyla (Agassiz, 1836)
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| Synonyms | |
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Taxonomy
editIt contains a single named species known from the Sinemurian-aged Blue Lias of Lyme Regis, England: S. polyspondyla Agassiz, 1836, with complete specimens representing both males and females. A second species from the same locality, S. tenuispina Woodward, 1886 (known from an isolated horn of a male), is now considered conspecific with S. polyspondyla.[1][2] In addition, the complete specimen of the female of an indeterminate species is known from the Sinemurian-aged Moltrasio Formation of Osteno, Italy, and indeterminate teeth are known from the earlier Hettangian of Belgium.[2][3][4]
Divergence estimates suggest that Squaloraja was a relict taxon and the last surviving member of a chimaera lineage that had diverged from the Chimaeroidei by the late Mississippian stage of the Carboniferous period, as stem-chimaeroids already appear in the fossil record by that point.[5] The predicted existence of a Paleozoic relative of Squaloraja was confirmed in 2023 with the description of the putative mid-Mississippian squalorajoid Sulcacanthus, which had a similar elongated rostrum, although it is unknown if it had a similar ovate shape. Between these two genera is a ghost lineage of more than 130 million years.[4]
Description
editSqualoraja was most closely related to modern chimaeras, but appeared completely unlike any living chimaera. Individuals of Squaloraja had flattened, ray-like bodies with enormous, flattened rostra that comprised half of the body length & were lined with limited denticles, giving them a superficial resemblance to a sawfish with a very wide, ovate "saw". Males had a cephalic clasper extending out from just above the rostrum that resembled a long, horn-like process.[6]
History
editThe type specimen was found by Mary Anning in 1829. This specimen was held at the Bristol Museum, and aside from the tail, was destroyed during The Blitz. The taxon was first described as Squalo-raia dolichognathos by Henry Riley in 1833 based on Anning's specimen, who identified it as a chondrichthyan with features of both sharks and rays, but this description was not publicly released until several years later. In 1836, Louis Agassiz described the species as Spinacorhinus polyspondylus based on the same specimen. Following the publishing of Riley's description, Agassiz amended the genus name in 1843 to Squaloraja, but retained his own species name. This overriding of Riley's species name violates the principle of priority, but Agassiz's name has been retained due to its longtime use in the scientific literature.[4]
During description, Agassiz noted the similarity of the specimen to the sawshark Pristiophorus. In 1890, George Bond Howes was the first researcher to identify Squaloraja as a holocephalan.[4]
See also
editReferences
edit- ^ a b "PBDB Taxon". paleobiodb.org. Retrieved 2024-08-17.
- ^ a b Duffin, Christopher J.; Garassino, Alessandro; Pasini, Giovanni (2023-05-19). "Squaloraja Riley 1833 (Holocephala: Squalorajidae) from the Lower Jurassic of Osteno Konservat-Lagerstätte (Como, NW Italy)". Natural History Sciences. 10 (1). doi:10.4081/nhs.2023.642. ISSN 2385-0922.
- ^ Delsate, D.; Duffin, C. J.; Weis, R. (2002). A new microvertebrate fauna from the Middle Hettangian (Early Jurassic) of Fontenoille (Province of Luxembourg, south Belgium). Geological Survey of Belgium.
- ^ a b c d Itano, Wayne M.; Duffin, Christopher J. (2023). "An enigmatic chondrichthyan spine from the Visean of Indiana, USA that resembles a median rostral cartilage of Squaloraja (Holocephali, Chimaeriformes)". Spanish Journal of Paleontology. 38 (1).
- ^ Lebedev, Oleg A.; Popov, Evgeny V.; Bagirov, Sergey V.; Bolshiyanov, Igor P.; Kadyrov, Rail I.; Statsenko, Evgeny O. (2021-06-18). "The earliest chimaeriform fish from the Carboniferous of Central Russia". Journal of Systematic Palaeontology. 19 (12): 821–846. doi:10.1080/14772019.2021.1977732. ISSN 1477-2019.
- ^ Welten, Monique; Smith, Moya Meredith; Underwood, Charlie; Johanson, Zerina (2015). "Evolutionary origins and development of saw-teeth on the sawfish and sawshark rostrum (Elasmobranchii; Chondrichthyes)". Royal Society Open Science. 2 (9): 150189. doi:10.1098/rsos.150189. ISSN 2054-5703. PMC 4593678. PMID 26473044.
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