Eileanchelys

Last updated

Eileanchelys
Temporal range: Middle Jurassic, 164  Ma
O
S
D
C
P
T
J
K
Pg
N
Scientific classification OOjs UI icon edit-ltr.svg
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Class: Reptilia
Clade: Pantestudines
Clade: Testudinata
Clade: Mesochelydia
Genus: Eileanchelys
Anquetin et al., 2009
Type species
Eileanchelys waldmani
Anquetin et al., 2009

Eileanchelys is an extinct genus of primitive turtle from the Middle Jurassic (Bathonian) period some 164 million years ago of Britain. Only one species is recorded, Eileanchelys waldmani. It is the best-represented turtle from the Middle Jurassic, because of the amount of specimens that can be assigned to it. The turtle is also one of the oldest turtles ever found to be aquatic, and might represent a milestone in turtle evolution.

Contents

Discovery and naming

In 2009, two specimens from the National Museums of Scotland, Edinburgh, including NMS G 2004.31.15 and NMS G 2004.31.16a–f, were found to differ from other turtles from the area and age. It was decided that they represented a new genus and species, and were named Eileanchelys waldmani by Jérémy Anquetin and his colleagues. The specimen NMS G 2004.31.15 was designated as the holotype, and NMS G 2004.31.16a-f, the paratypes. NMS G 2004.31.16 includes at least five, and possibly six, different individuals, all in one block. The holotype of Eileanchelys is a partial skull. Both blocks were found in Cladach a'Ghlinne, Scotland. [1]

Etymology

Eileanchelys waldmani was named and described by Anquetin et al. in 2009. The generic name, eilean, comes from the Scottish Gaelic word for island, and chelys, from the Greek word for turtle. The species was named in honour of Dr. Michael Waldman who found its remains, as well as the first Scottish Jurassic mammal, after rediscovering the Cladach a'Ghlinne locality. [1]

Description

Eileanchelys is a small turtle, with an approximate carapace length of 20 to 30 centimetres (7.9 to 11.8 in). [2] The preserved carapaces of Eileanchelys are all slightly crushed, but show that they were lightly domed in real life. Therefore, the morphology of its shell was similar to Kayentachelys . There is a fused connection of the carapace and plastron in Eileanchelys. The connection is not found in Heckerochelys , but is in Kayentachelys. [1]

Distinguishing characteristics

Eileanchelys is characterized by the following features: the presence of nasal; elongated postorbital skull; [2] absence of flooring of the cavum acustico-jugulare; processus interfenestralis of the opisthotic more slender than that of more basal forms but more robust than that of crown-group turtles; separate openings of the canalis cavernosum and canalis stapedio-temporalis present within the cavum acustico-jugulare; a reduced thickness of the basicranium floor comparable with that of crown-group turtles; well-developed antrum postoticum; flat and horizontal vomer that is free of contacts for most of its length except at its extremities and along a short suture with the prefrontal; absence of processus trochlearis oticum; posteroventrally open incisura columellae auris; at least eight neurals (an additional plate between neural 8 and suprapygal 1 may be a ninth neural or a supernumerary suprapygal), two broad suprapygals, and eight costals present; absence of carapacial or plastral fontanelle in adult individuals; one short but broad cervical scute present; vertebral scutes wider than pleurals; vertebral 3–4 sulcus on neural 6; reduced cleithrum present; arrow-shaped entoplastron that does not separate the epiplastra anteriorly; one pair of mesoplastra that meet medially; one small pair of extragulars present; and anal scute that does not reach the hypoplastron. [1]

Classification

Eileanchelys is a stable taxon, which means that its classification does not differ much in cladograms. It is related to both Heckerochelys and Kayentachelys, although often it is found to be derived from the later. The below cladogram illustrates the relationships of basal testudinata: [1]

Testudinata

Hypothetical ancestor

Proganochelys quenstedti

Palaeochersis talampayensis

Australochelys africanus

Proterochersis robusta

Kayentachelys aprix

Eileanchelys waldmani

Heckerochelys romani

Condorchelys antiqua

Meiolania platyceps

Mongolochelys efremovi

Testudines

Paleoecology

Habitat

Eileanchelys lived in the Kilmaluag Formation, which has a Late Bathonian age. The formation is made up entirely of mudstone, shale and some limestone, and, as many aquatic types of animals have been found in it and land vertebrates are rare, it was almost certainly marine. Therefore, Eileanchelys was most likely was an aquatic turtle, [2] swimming throughout lagoons and lakes, rather than terrestrial animal that died in a body of water. It is therefore one of the oldest, and best known, extinct aquatic turtles, and might represent a new evolutionary stage of turtle. [1]

Fauna

Eileanchelys existed in the Kilmaluag Formation of the Great Estuarine Group. This formation has an abundance of tetrapod fauna, including salamanders; the choristodere Cteniogenys sp.; crocodilians; the lepidosauromorph Marmoretta sp.; various lizards; pterosaurs; dinosaurs; the synapsid Stereognathus hebridicus ; and early mammals. [1]

Related Research Articles

<i>Yangchuanosaurus</i> Metriacanthosaurid theropod dinosaur genus from Middle Jurassic period.

Yangchuanosaurus is an extinct genus of metriacanthosaurid theropod dinosaur that lived in China from the Middle Jurassic to Early Cretaceous periods, and was similar in size and appearance to its North American and European relative, Allosaurus. Yangchuanosaurus hails from the Upper Shaximiao Formation and Suining Formation and was the largest predator in a landscape that included the sauropods Mamenchisaurus and Omeisaurus and the stegosaurs Chialingosaurus, Tuojiangosaurus and Chungkingosaurus. This theropod was named after the area in which was discovered, Yongchuan, in China.

<i>Isanosaurus</i> Genus of dinosaurs

Isanosaurus is an extinct genus of sauropod dinosaur from Thailand. It was originally dated to approximately 210 million years ago during the Late Triassic, which would make it one of the oldest known sauropods. Its age was later considered uncertain, and may be Early Jurassic or even as young as Late Jurassic. The only species is Isanosaurus attavipachi. Though important for the understanding of sauropod origin and early evolution, Isanosaurus is poorly known. Exact relationships to other early sauropods remain unresolved.

<i>Monolophosaurus</i> Extinct genus of dinosaurs

Monolophosaurus is an extinct genus of tetanuran theropod dinosaur from the Middle Jurassic Shishugou Formation in what is now Xinjiang, China. It was named for the single crest on top of its skull. Monolophosaurus was a mid-sized theropod at about 5–5.5 metres (16–18 ft) long and weighed 475 kilograms (1,047 lb).

Chuandongocoelurus is a genus of carnivorous tetanuran theropod dinosaur from the Jurassic of China.

<i>Eurhinosaurus</i> Genus of leptonectid ichthyosaur from the Early Jurassic period

Eurhinosaurus is an extinct genus of ichthyosaur from the Early Jurassic (Toarcian), ranging between 183 and 175 million years. Fossils of the aquatic reptile have been found in Western Europe. They used to live in the deep, open sea area. Eurhinosaurus was a large genus of ichthyosaurs. An adult individual could reach up to 7 metres (23 ft) in length.

<span class="mw-page-title-main">Turiasauria</span> Extinct clade of dinosaurs

Turiasauria is an unranked clade of basal sauropod dinosaurs known from Middle Jurassic to Early Cretaceous deposits in Europe, North America, and Africa.

Dahl's toad-headed turtle is a medium-sized species of side-necked turtle in the family Chelidae. This critically endangered freshwater turtle is endemic to northern Colombia, where it lives in small pools, streams, and swamps, but aestivates on land.

<span class="mw-page-title-main">Protostegidae</span> Extinct family of turtles

Protostegidae is a family of extinct marine turtles that lived during the Cretaceous period. The family includes some of the largest sea turtles that ever existed. The largest, Archelon, had a head one metre (39 in) long. Like most sea turtles, they had flattened bodies and flippers for front appendages; protostegids had minimal shells like leatherback turtles of modern times.

<span class="mw-page-title-main">Turtle shell</span> Shield for the ventral and dorsal parts of turtles

The turtle shell is a shield for the ventral and dorsal parts of turtles, completely enclosing all the vital organs of the turtle and in some cases even the head. It is constructed of modified bony elements such as the ribs, parts of the pelvis and other bones found in most reptiles. The bone of the shell consists of both skeletal and dermal bone, showing that the complete enclosure of the shell likely evolved by including dermal armor into the rib cage.

<span class="mw-page-title-main">Goniopholididae</span> Extinct family of reptiles

Goniopholididae is an extinct family of moderate-sized semi-aquatic neosuchian crocodyliformes. Their bodyplan and morphology are convergent on living crocodilians. They lived across Laurasia between the Middle Jurassic and the Late Cretaceous.

<i>Anoualerpeton</i> Extinct genus of amphibians

Anoualerpeton is an extinct genus of lissamphibian in the family Albanerpetontidae. It is the oldest and most primitive albanerpetontid known. Fossils have been found of two different species, Anoualerpeton priscus from the Middle Jurassic (Bathonian) aged Forest Marble and Kilmaluag formations of England and Scotland, and Anoualerpeton unicus from Late Jurassic-Early Cretaceous (Tithonian-Berriasian) Ksar Metlili Formation of Morocco. A. unicus is the only named albanerpetontid from Gondwana.

<i>Cteniogenys</i> Genus of reptiles

Cteniogenys is a genus of choristodere, a morphologically diverse group of aquatic reptiles. It is part of the monotypic family Cteniogenidae. The type and only named species, C. antiquus, was named in 1928 by Charles W. Gilmore. The holotype, VP.001088, was collected in the Morrison Formation, Wyoming in 1881 by William H. Reed. More specimens have been discovered since then, including specimens from the Late Jurassic of Portugal and Middle Jurassic of Britain, which have not been assigned to species.

<i>Kayentachelys</i> Extinct genus of turtles

Kayentachelys is an extinct genus of turtle known only from the "silty facies" of the Lower Jurassic Kayenta Formation in northeastern Arizona on the lands of the Navajo Nation.

Australochelys is an extinct genus of rhaptochelydian turtle. It is known from one species, A. africanus, that came from the Elliot Formation of South Africa. The holotype of Australochelys consists of only a skull and a fragment of the carapace, which shows both primitive and derived features. Like Proganochelys, Australochelys has large orbits and a ventral basioccipital tubercle, but like derived turtles such as casichelydians, a group containing Cryptodira and Pleurodira, it possesses a sutured basipterygoidal attachment, and a middle ear region partially enclosed laterally. These characteristics show that Australochelys is more closely related to casichelydians than to Proganochelys, and together with the former, it makes up Rhaptochelydia. The skull of Australochelys shows that an advanced hearing mechanism of turtles evolved before the appearance of modern turtles.

<span class="mw-page-title-main">Kilmaluag Formation</span> Geologic formation in Scotland

The Kilmaluag Formation is a Middle Jurassic geologic formation in Scotland. It was formerly known as the Ostracod Limestone for preserving an abundance of fossil freshwater/low salinity ostracods. Gastropods, bivalves, trace fossil burrows, and vertebrate fossil remains have also been recorded from the formation. Vertebrate fossils include fish, crocodylomorphs, mammals, small reptiles, amphibians, theropod and sauropod dinosaurs and pterosaurs.

<i>Basilemys</i> Extinct genus of turtles

Basilemys is a large, terrestrial nanhsiungchelyid turtle from the Upper Cretaceous of North and Central America. Basilemys has been found in rocks dating to the Campanian and Maastrichtian subdivisions of the Late Cretaceous and is considered to be the largest terrestrial turtle of its time. In an analysis made by Sukhanov et al. on a nansiunghelyid turtle from the Upper Cretaceous of Mongolia, it was demonstrated that Asian nanhsiungchelyids gave rise to the North American nanhsiungchelyids.

Wareolestes rex is a mammaliaform from the Middle Jurassic (Bathonian) rocks of England and Scotland. It was originally known from isolated teeth from England, before a more complete jaw with teeth was found in the Kilmaluag Formation of Skye, Scotland.

<span class="mw-page-title-main">Mesochelydia</span> Clade of reptiles

Mesochelydia is a clade within Pantestudines, more inclusive than Perichelydia, but less than Testudinata. The clade is known from the Early Jurassic to the Present, and contains all Jurassic representatives of Testudinata aside from Australochelys. The ancestral condition for Mesochelydia is thought to be aquatic, as opposed to terrestrial for Testudinata. They are distinguished from more basal testudinatans by the presence of the following characters: strap like pectoral girdle, supramarginals absent, reduced posterior entoplastral process, eleven pairs of peripherals, elongate processus interfenestralis, paired basioccipital tubercles, fully formed cavum tympani and antrum postoticum, single vomer, confluent external nares, lacrimals and supratemporals absent.

Itapecuruemys is an extinct genus of bothremydid pleurodiran turtle that was discovered in the Itapecuru Formation of Brazil. It is a monotypic genus, with only type species Itapecuruemys amazoniensis known.

Michael Waldman is a British palaeontologist known for his work on fossil fish, mammals, and reptiles. He also discovered the globally important fossil site of Cladach a'Ghlinne, near Elgol on the Isle of Skye, Scotland. This site exposes the Kilmaluag Formation and provides a valuable record of Middle Jurassic ecosystems. During the 1970s he visited the site several times with fellow palaeontologist Robert Savage. The fossil turtle Eileanchelys waldmani was named after Michael in recognition of his notable contribution to palaeontology.

References

  1. 1 2 3 4 5 6 7 Anquetin, J.; Barrett, P.M.; Jones, M.E.H.; Moore-Fay, S.; Evans, S.E. (2009). "A new stem turtle from the Middle Jurassic of Scotland: new insights into the evolution and palaeoecology of basal turtles". Proceedings of the Royal Society B: Biological Sciences . 276 (1658): 879–886. doi:10.1098/rspb.2008.1429. ISSN   0962-8452. PMC   2664364 . PMID   19019789.
  2. 1 2 3 Hans-Dieter Sues (August 6, 2019). The Rise of Reptiles. 320 Million Years of Evolution. Johns Hopkins University Press. p. 53. ISBN   9781421428680.