Aigialosuchus

Aigialosuchus is a genus of long-snouted crocodylomorph that lived in what is now Sweden during the Campanian stage of the Late Cretaceous period and possibly in what is now Denmark during the Paleocene stage of the Paleogene period. The name Aigialosuchus comes from the Greek αἰγιαλός (aigialos), meaning "seashore", and σοῦχος (souchus), meaning "crocodile". The genus contains a single species, A. villandensis, described in 1959 by Per Ove Persson based on material recovered from the Kristianstad Basin in southern Sweden.

Aigialosuchus
Temporal range: Early Campanian
83.5–80.5 Ma
↓
Possible Early Paleocene record
Teeth attributed to Aigialosuchus sp. found in the Kristianstad Basin and exhibited at "Havsdrakarnas hus" in Bromölla, Sweden
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Reptilia
Family: †Dyrosauridae
Genus: †Aigialosuchus
Persson, 1959
Species:
†A. villandensis
Binomial name
†Aigialosuchus villandensis
Persson, 1959

The known fossil material of Aigialosuchus consists of a partial skull and isolated teeth from southern Sweden, with possible additional teeth found on Zealand in Denmark. The fragmentary nature of these remains means that the precise classification of the genus remains uncertain. Though typically classified as an eusuchian until recently, most recent research places it within the more basal family Dyrosauridae.

In the Cretaceous, southern Scandinavia was covered by shallow sea and the Ivö Klack site within the Kristianstad Basin, where most of the fossils referred to Aigialosuchus have been found, was a small and rocky island. Many other dyrosaurids were marine, a lifestyle possibly shared by Aigialosuchus since its fossil have been discovered in marine deposits. Its teeth were short and stout, possibly an adaptation towards feeding on large fish and invertebrates.

Description

Aigialosaurus was a long- and narrow-snouted crocodylomorph.[1][2][3] In contrast to modern crocodylians, which typically have long and slender teeth, the teeth of Aigialosuchus were short and stout.[2]

History of research

Aigialosuchus was described by Swedish paleontologist Per-Ove Persson in 1959 based on fossil material recovered at the Ivö Klack locality in the Kristianstad Basin. The generic name derives from the Greek αἰγιαλός (aigialos), meaning "seashore", and σοῦχος (souchus), meaning "crocodile".[1] The species name of the only species referred to the genus, A. villandensis, derives from the Villand district of Skåne, where the fossils were found. The material Persson based Aigialosuchus on were the remains of the anterior part of the skull and of the mandibles, including some detached teeth, belonging to a single individual. Persson considered this material to be enough to clearly differentiate the fossil animal from all other known long-snouted crocodylomorphs, noting that the main distinguishing feature was the nasal bone of Aigialosuchus extending to the fenestra exonarina communis.[4]

In 2017, Greenlandic paleontologist Jan S. Adolfssen, Danish paleontologist Jesper Milàn and American paleontologist Matt Friedman noted that a single, rather blunt and wide crocodylomorph tooth from the Faxe quarry in the Middle Danian-aged Faxe Formation at Faxe, Denmark, might be referrable to either Aigialosuchus or to some genus within the Alligatoroidea.[5] A similar tooth also discovered in Early to Middle Paleocene deposits, this time at Gemmas Allé in Copenhagen, in 2014, also accorded well with Persson's description of Aigialosuchus teeth, though it was not referred to the genus due to the lack of a formal comparison to the type material.[6]

Classification
Reconstruction of Dyrosaurus, another long-snouted and marine dyrosaurid crocodylomorph

Persson classified Aigialosuchus as a true crocodile, placing it within the subfamily Crocodylinae.[1] He based this on the fact that the foremost part of the snout of Aigialosuchus was bounded off from the rest of the head by a paired notch and broadened. Persson also noted that since Aigialosuchus is quite poorly known, detailed comparisons with other crocodylines was impossible.[4]

Persson's classification of Aigialosuchus as a crocodyline is no longer considered likely. Because of the fragmentary material, Aigialosuchus was considered a problematic taxon by French paleontologist Jeremy E. Martin and Italian paleontologist Massimo Delfino in 2010, though they noted that it was likely to have been an eusuchian. Although the narrow snout of Aigialosuchus is similar to the narrow snouts within the genera in the Gavialoidea, they considered it to be unlikely that Aigialosuchus is part of that superfamily on account of the nasal of Aigialosuchus contributing to the posterior margin of the external naris.[6]

In 2014, German paleontologist Daniela Schwarz-Wings and Danish paleontologists Jesper Milàn and Palle Gravesen considered the features of Aigialosuchus to accord better with the Crocodyloidea than with the Gavialoidea, but noted that Aigialosuchus significantly predated the earliest similar crocodyloids genera. Schwarz-Wings, Milàn and Gravesen noted that until a taxonomic revision of the Aigialosuchus material is carried out, its precise systematic position within the entire Crocodylomorpha will remain unclear.[6]

In 2014, French paleontologists Jeremy E. Martin, Romain Amiot and Christophe Lécuyer and English paleontologist Michael J. Benton noted that Persson's description of Aigialosuchus accorded well with the known material of known contemporary freshwater eusuchians.[7]

More recent research, from 2015 onwards, typically classifies Aigialosuchus as a dyrosaurid.[3][8][9]

Paleoecology

Certain fossils of Aigialosuchus have only been recovered from the Campanian-age deposits in the Kristianstad Basin in Sweden. During the Campanian, the Kristianstad Basin was a subtropical to temperate shallow inland sea home to a diverse marine fauna characteristic of shallow marine life of an inner shelf community and included abundant algae, brachiopods, bryozoans, molluscs (including bivalves, gastropods, belemnites and the ammonites), sea urchins, serpulids, decapods and sponges.[10][11] Additionally, fish (including a vast array of sharks) were also common and fossils of many species of reptiles, most of them marine, have also been found, including mosasaurs, sea turtles, crocodylmorphs and a few dinosaurs.[12]

The fossils of Aigialosuchus described by Persson in 1959 were recovered from marine sediments, though Persson noted that this was not necessarily an indicator that Aigialosuchus itself would have been purely marine. According to Persson, Aigialosuchus could also have lived in the littoral zone or in a river adjacent to the mainland.[4] Within the Kristianstad Basin, the fossil site Ivö Klack has yielded the most Aigialosuchus fossils. Ivö Klack was a small, rocky island during the Cretaceous. The presence of Aigialosuchus at the site might indicate that Aigialosuchus preferred to live in coastal waters, where it could lay its egg on adjacent land, rest and heat up, similar to modern crocodilians.[13]

Most recent and modern long-snouted crocodylomorphs (notably the gharials) have slender and long teeth, being piscivores. The teeth of Aigialosuchus were stout and short, meaning that it would probably have been adapted to some other form of feeding. According to Swedish paleontologist Elisabeth Einarsson, the robust teeth of Aigialosuchus indicates that it was adapted for feeding on larger fish, such as Enchodus, and larger invertebrates. Contrary to Persson's assessment, Aigialosuchus is now believed to have been a marine animal, similar to other dyrosaurids.[2]

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References
  1. Persson 1959, p. 470.
  2. Einarsson 2018, p. 37.
  3. Einarsson 2018, p. 28.
  4. Persson 1959, p. 471.
  5. Adolfssen, Milàn & Friedman 2017, p. 11.
  6. Schwarz-Wings, Milàn & Gravesen 2014, p. 23.
  7. Martin et al. 2014, p. 5.
  8. Källsten 2015, p. 3.
  9. Kear et al. 2016, p. 6.
  10. Lindgren 1998, p. 5.
  11. Einarsson 2018, p. 27–30.
  12. Hajny 2014, p. 7.
  13. Sørensen, Surlyk & Lindgren 2013, p. 90.

Cited bibliography
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