Eileanchelys
Middle Jurassic aquatic turtle from Scotland.
Eileanchelys is an extinct genus of primitive turtle from the Middle Jurassic (Bathonian) of Britain, known from a single species, Eileanchelys waldmani. It is the best-represented turtle from the Middle Jurassic due to the number of specimens assigned to it. The genus is notable as one of the oldest known aquatic turtles and may represent a milestone in turtle evolution.
Quick Facts
- Type species
- Eileanchelys waldmani
Facts from the source article.
Discovery and naming
In 2009, two specimens from the National Museums of Scotland, Edinburgh (NMS G 2004.31.15 and NMS G 2004.31.16a–f), were recognized as distinct from other turtles of the same area and age. Jérémy Anquetin and colleagues designated them as a new genus and species, Eileanchelys waldmani. The holotype is a partial skull, and the paratypes include at least five individuals in one block. Both blocks came from Cladach a'Ghlinne, Scotland. The generic name combines the Scottish Gaelic eilean (island) with the Greek chelys (turtle); the species honors Dr. Michael Waldman, who discovered the remains and rediscovered the locality.
Description
Eileanchelys was a small turtle with a carapace length of about 20 to 30 cm. Its preserved carapaces are slightly crushed but indicate a lightly domed shell, similar in morphology to Kayentachelys. The carapace and plastron are fused, a connection absent in Heckerochelys but present in Kayentachelys. Distinctive features include: a nasal bone; an elongated postorbital skull; absence of flooring of the cavum acustico-jugulare; a slender processus interfenestralis of the opisthotic; separate openings of the canalis cavernosum and canalis stapedio-temporalis within the cavum acustico-jugulare; reduced basicranium floor thickness; a well-developed antrum postoticum; a flat, horizontal vomer free of contacts except at its extremities and along a short suture with the prefrontal; absence of a processus trochlearis oticum; a posteroventrally open incisura columellae auris; at least eight neurals, two broad suprapygals, and eight costals; no carapacial or plastral fontanelle in adults; one short, broad cervical scute; vertebral scutes wider than pleurals; a reduced cleithrum; an arrow-shaped entoplastron not separating the epiplastra anteriorly; one pair of mesoplastra meeting medially; one small pair of extragulars; and an anal scute not reaching the hypoplastron.
Paleoecology
The Kilmaluag Formation, dating to the Late Bathonian, is composed of mudstone, shale, and some limestone. Because its fossils are mostly aquatic animals with very few land vertebrates, the environment was almost certainly marine. This means Eileanchelys was an aquatic turtle that swam in lagoons and lakes, not a land animal that happened to die in water. It ranks among the oldest and best-known extinct aquatic turtles and could mark a new step in turtle evolution. The same formation also holds a rich mix of tetrapods: salamanders, the choristodere Cteniogenys sp., crocodilians, the lepidosauromorph Marmoretta sp., various lizards, pterosaurs, dinosaurs, the synapsid Stereognathus hebridicus, and early mammals.
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