| Eileanchelys | |
|---|---|
Scientific classification | |
| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Reptilia |
| Clade: | Pantestudines |
| Clade: | Testudinata |
| Clade: | Mesochelydia |
| Genus: | †Eileanchelys Anquetinet al.,2009 |
| Type species | |
| Eileanchelys waldmani Anquetinet al., 2009 | |
Eileanchelys is an extinct genus ofprimitive turtle from the MiddleJurassic (Bathonian) period some 164 million years ago ofBritain. Only one species is recorded,Eileanchelys waldmani. It is the best-represented turtle from theMiddle 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 beaquatic, and might represent a milestone in turtle evolution.
In2009, two specimens from theNational 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 namedEileanchelys waldmani byJérémy Anquetin and his colleagues. The specimen NMS G 2004.31.15 was designated as theholotype, and NMS G 2004.31.16a-f, theparatypes. NMS G 2004.31.16 includes at least five, and possibly six, different individuals, all in one block. The holotype ofEileanchelys is a partial skull. Both blocks were found inCladach a'Ghlinne,Scotland.[1]
Eileanchelys waldmani was named and described by Anquetinet al. in 2009. The generic name,eilean, comes from the Scottish Gaelic word for island, andchelys, 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]
Eileanchelys is a small turtle, with an approximatecarapace length of 20 to 30 centimetres (7.9 to 11.8 in).[2] The preserved carapaces ofEileanchelys are all slightly crushed, but show that they were lightly domed in real life. Therefore, the morphology of its shell was similar toKayentachelys. There is a fused connection of the carapace andplastron inEileanchelys. The connection is not found inHeckerochelys, but is inKayentachelys.[1]
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]
Eileanchelys is a stable taxon, which means that its classification does not differ much incladograms. It is related to bothHeckerochelys andKayentachelys, although often it is found to bederived from the later. The below cladogram illustrates the relationships of basaltestudinata:[1]
Eileanchelys lived in theKilmaluag Formation, which has a LateBathonian age. The formation is made up entirely ofmudstone,shale and somelimestone, and, as manyaquatic types ofanimals 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]
Eileanchelys existed in the Kilmaluag Formation of theGreat Estuarine Group. This formation has an abundance oftetrapod fauna, includingsalamanders; thechoristodereCteniogenys sp.;crocodilians; thelepidosauromorphMarmoretta sp.; variouslizards;pterosaurs;dinosaurs; thesynapsidStereognathus hebridicus; and earlymammals.[1]
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