''Eileanchelys'' is an extinct genus of primitive turtle from the Middle

Jurassic The Jurassic ( ) is a geologic period and stratigraphic system that spanned from the end of the Triassic Period million years ago (Mya) to the beginning of the Cretaceous Period, approximately Mya. The Jurassic constitutes the middle period of ...

(

Bathonian In the geologic timescale the Bathonian is an age and stage of the Middle Jurassic. It lasted from approximately 168.3 Ma to around 166.1 Ma (million years ago). The Bathonian Age succeeds the Bajocian Age and precedes the Callovian Age. Str ...

) period some 164 million years ago of

Britain Britain most often refers to: * The United Kingdom, a sovereign state in Europe comprising the island of Great Britain, the north-eastern part of the island of Ireland and many smaller islands * Great Britain, the largest island in the United King ...

. 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.

Discovery and naming

In 2009, two specimens from the

National Museums of Scotland National Museums Scotland (NMS; gd, Taighean-tasgaidh Nàiseanta na h-Alba) is an executive non-departmental public body of the Scottish Government. It runs the national museums of Scotland. NMS is one of the country's National Collections ...

Edinburgh Edinburgh ( ; gd, Dùn Èideann ) is the capital city of Scotland and one of its 32 council areas. Historically part of the county of Midlothian (interchangeably Edinburghshire before 1921), it is located in Lothian on the southern shore of t ...

, 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 A holotype is a single physical example (or illustration) of an organism, known to have been used when the species (or lower-ranked taxon) was formally described. It is either the single such physical example (or illustration) or one of sever ...

, and NMS G 2004.31.16a-f, the

paratype In zoology and botany, a paratype is a specimen of an organism that helps define what the scientific name of a species and other taxon actually represents, but it is not the holotype (and in botany is also neither an isotype nor a syntype). O ...

s. 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 Scotland (, ) is a Countries of the United Kingdom, country that is part of the United Kingdom. Covering the northern third of the island of Great Britain, mainland Scotland has a Anglo-Scottish border, border with England to the southeast ...

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.

Description

''Eileanchelys'' is a small turtle, with an approximate carapace length of . 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 ''Kayentachelys'' ("Kayenta turtle") 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. History of discovery and significance The e ...

''. There is a fused connection of the carapace and plastron in ''Eileanchelys''. The connection is not found in '' Heckerochelys'', but is in ''Kayentachelys''.

Distinguishing characteristics

''Eileanchelys'' is characterized by the following features: the presence of nasal; elongated postorbital skull; 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.

Classification

''Eileanchelys'' is a stable taxon, which means that its classification does not differ much in

cladogram A cladogram (from Greek ''clados'' "branch" and ''gramma'' "character") is a diagram used in cladistics to show relations among organisms. A cladogram is not, however, an evolutionary tree because it does not show how ancestors are related to ...

s. It is related to both ''Heckerochelys'' and ''Kayentachelys'', although often it is found to be

derived Derive may refer to: * Derive (computer algebra system), a commercial system made by Texas Instruments * ''Dérive'' (magazine), an Austrian science magazine on urbanism *Dérive, a psychogeographical concept See also * *Derivation (disambiguatio ...

from the later. The below cladogram illustrates the relationships of basal

testudinata Testudinata is the group of all tetrapods with a true turtle shell. It includes both modern turtles (Testudines) and many of their extinct, shelled relatives (stem-turtles). Though it was first coined as the group containing turtles by Jacob The ...

Paleoecology

Habitat

''Eileanchelys'' lived in the

Kilmaluag Formation The Kilmaluag Formation is a Middle Jurassic geologic formation in Scotland. It was formerly known as the Ostracod Limestone for the abundance of fossil freshwater ostracods within it. The Kilmaluag Formation is very fossiliferous, with ostracods ...

, which has a Late

age. The formation is made up entirely of mudstone, shale and some

limestone Limestone ( calcium carbonate ) is a type of carbonate sedimentary rock which is the main source of the material lime. It is composed mostly of the minerals calcite and aragonite, which are different crystal forms of . Limestone forms whe ...

, and, as many aquatic types of

animal Animals are multicellular, eukaryotic organisms in the Kingdom (biology), biological kingdom Animalia. With few exceptions, animals Heterotroph, consume organic material, Cellular respiration#Aerobic respiration, breathe oxygen, are Motilit ...

s have been found in it and land vertebrates are rare, it was almost certainly marine. Therefore, ''Eileanchelys'' was most likely was an aquatic turtle, 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.

Fauna

''Eileanchelys'' existed in the Kilmaluag Formation of the Great Estuarine Group. This formation has an abundance of

tetrapod Tetrapods (; ) are four-limbed vertebrate animals constituting the superclass Tetrapoda (). It includes extant and extinct amphibians, sauropsids ( reptiles, including dinosaurs and therefore birds) and synapsids ( pelycosaurs, extinct t ...

fauna, including

salamander Salamanders are a group of amphibians typically characterized by their lizard-like appearance, with slender bodies, blunt snouts, short limbs projecting at right angles to the body, and the presence of a tail in both larvae and adults. All t ...

s; the

choristodere Choristodera (from the Greek χωριστός ''chōristos'' + δέρη ''dérē'', 'separated neck') is an extinct order of semiaquatic diapsid reptiles that ranged from the Middle Jurassic, or possibly Triassic, to the late Miocene (168 to ...

Cteniogenys ''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 ho ...

'' sp.;

crocodilia Crocodilia (or Crocodylia, both ) is an order of mostly large, predatory, semiaquatic reptiles, known as crocodilians. They first appeared 95 million years ago in the Late Cretaceous period ( Cenomanian stage) and are the closest livi ...

ns; the

lepidosauromorph Lepidosauromorpha (in PhyloCode known as ''Pan-Lepidosauria'') is a group of reptiles comprising all diapsids closer to lizards than to archosaurs (which include crocodiles and birds). The only living sub-group is the Lepidosauria, which cont ...

Marmoretta ''Marmoretta'' is an extinct genus of small lepidosauromorph reptile known from the Middle Jurassic (late Bathonian age) of Oxfordshire, England and Skye, Scotland. It contains a single species, ''Marmoretta oxoniensis''. Etymology ''Marmoretta ...

'' sp.; various lizards; pterosaurs;

dinosaur Dinosaurs are a diverse group of reptiles of the clade Dinosauria. They first appeared during the Triassic period, between 243 and 233.23 million years ago (mya), although the exact origin and timing of the evolution of dinosaurs is t ...

s; the

synapsid Synapsids + (, 'arch') > () "having a fused arch"; synonymous with ''theropsids'' (Greek, "beast-face") are one of the two major groups of animals that evolved from basal amniotes, the other being the sauropsids, the group that includes reptil ...

'' Stereognathus hebridicus''; and early mammals.

References

External links

Earliest Swimming Turtle Fossils Found -- New SpeciesBBC NEWS , Science & Environment , Ancient turtle discovered on Skye‘Missing link’ turtle was swimming with dinosaurs
* ttp://www.independent.ie/world-news/europe/missing-link-turtle-swam-with-dinosaurs-1544201.html 'Missing link' turtle swam with dinosaurs - Europe - Independent.ie {{Taxonbar, from=Q3501209 Middle Jurassic reptiles of Europe Transitional fossils Fossil taxa described in 2009 Prehistoric turtle genera