Basilemys
Basilemys (IPA: [bæsɪlɛmiːs]) is a large, terrestrial trionychoid turtle from the Upper Cretaceous.[1] In Greek, the word "Basil" means royal or kingly and the word "Emys" means turtle. Therefore, Basilemys means King Turtle. 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.[2] Basilemys has solely been found in North America.[3] The family Nanhsiungchelyidae, which is the family Basilemys belongs to, made its first appearance in the Lower Cretaceous, in what we now call Asia. Because of Basilemys, we know that this family appeared in North America in the Upper Cretaceous.[4] It is possible that Basilemys and other nanhsiungchelyids are immigrants from Asia. They might have arrived in North America by passing through what we now call the Bering Strait somewhere during the Cretaceous.[4] In an analysis made by Sukhanov et al. on a new Nansiunghelyid turtle from the Upper Cretaceous of Mongolia, it was demonstrated that Asian nanhsiungchelyids gave rise to the North American nanhsiungchelyids.[5] Basilemys shares some traits with another member of nanhsiungchelyidae, Zangerlia, which is similar to Basilemys in, for example, skull proportions.[6] However, Basilemys has a more complex triturating surface that includes well-defined pockets on the dentary, and it also has tooth-like projections on the triturating surface of the maxilla.[6]
From the species in nanhsiungchelyidae, Basilemys is considered to be most similar to tortoises.[3] Many paleontologists have described the behaviors of Basilemys to likely be comparable to that of tortoises, due to living in terrestrial habitats and consuming tough plants.[3] Moreover, the complex triturating surface of Basilemys indicates that they are similar to tortoises in being terrestrial herbivores.[6] Basilemys is easily distinguishable from other fossil turtles due to how thick its shell is, the intricate sculpture of rows of triangular tubercles separated by pits, and its reduced inframarginal scales.[2] The fossil record is abundant with material from the shell and with appendicular, but cranial and cervical material is quite rare for Basilemys.[1]
Turtles were prominent members of the Upper Cretaceous and thus, their specimens found throughout North America are useful in defining biogeographic patterns.[7] In 1924, a partial skeleton and crushed skull of Basilemys was collected by C.M. Sternberg from the Horseshoe Canyon Formation.[1] However, this specimen was poorly preserved and information of the skull could not be analyzed.[1] In another part of Canada, a Basilemys specimen from the Frenchman Formation of Saskatchewan retained most of the neck and cranial fragments.[1] This was groundbreaking because of how scarce cranial and cervical material is for Basilemys. Most of the well-preserved specimens of Basilemys are of the carapace, the hard upper shell of a turtle. Apart from the type species Basilemys variolosa, five other species have been described to date. These include B. gaffneyi, B. morrinensis, B. nobilis, B. praeclara and B. sinuosa. [1] In 2018, a nearly complete shell of B. morrinensis was found from the Horseshoe Canyon Formation of Alberta.[3] Basilemys specimens have also been found from the Oldman Formation and Dinosaur Park Formation.[6]
