Acamptonectes
Acamptonectes is a genus of ophthalmosaurid ichthyosaurs, a type of dolphin-like marine reptiles, that lived during the Early Cretaceous around 130 million years ago. The first specimen—a partial adult skeleton—was discovered in Speeton, England, in 1958, but was not formally described until 2012 by Valentin Fischer and colleagues. They also recognised a partial subadult skeleton belonging to the genus from Cremlingen, Germany, and specimens from other localities in England. The genus contains the single species Acamptonectes densus; the generic name means "rigid swimmer" and the specific name means "compact" or "tightly packed".
The scientific name of the genus refers to unusual adaptations in the body of Acamptonectes that made its trunk rigid, including tightly-fitting bones in the occiput (back and lower part of the skull) and interlocking vertebral centra ("bodies" of the vertebrae), which were likely adaptations that enabled it to swim at high speeds with a tuna-like form of locomotion. Other distinguishing characteristics include an extremely slender snout and unique ridges on the basioccipital bone of the braincase. As an ichthyosaur, Acamptonectes had large eye sockets and a tail fluke. Acamptonectes was similar in morphology to the related but earlier ophthalmosaurines Ophthalmosaurus and Mollesaurus.
The discovery of Acamptonectes had significant implications for the evolutionary history of ichthyosaurs. It was long believed the generalised platypterygiine ophthalmosaurids were the only lineage of ichthyosaurs that survived into the Early Cretaceous following a mass extinction of ichthyosaurs across the Jurassic–Cretaceous boundary. As one of the first-known ophthalmosaurine ophthalmosaurids from the Early Cretaceous, the discovery of Acamptonectes provided evidence against such a mass extinction. Although the larger eyes of Acamptonecteswould have made it better adapted than platypterygiines to depth diving, it was probably a generalist predator. Its teeth, which were slender and textured with longitudinal ridges, were adapted for impaling prey, which suggests it likely fed on soft, fleshy prey such as fish and squid.
Over a series of weekends in 1958, four students and a technician from Hull University's geology department collected a fossil specimen from the Speeton Clay Formation at Speeton in northern England. The fossil belonged to an ichthyosaur or "fish lizard", a Mesozoic group of marine reptiles;[1] it consists of a partial adult skeleton that includes a fragmentary skull roof, a mandible, vertebrae, ribs, and the scapular girdle (the shoulder area). In 1991, it was transferred to the Hunterian Museum of the University of Glasgow (GLAHM) when the geology department of Hull University was closed. It was catalogued under the specimen number GLAHM 132855,[2] and was also known as the "Speeton Clay ichthyosaur". Palaeontologist Robert M. Appleby described the specimen and assigned it to the genus Platypterygius as the species "P. speetoni" (which he considered primitive within that genus), in a monograph that remained unpublished at the time of his death in 2003. A second specimen of this ichthyosaur was found in 1985, also in the Speeton Clay, and is catalogued as NHMUK R11185 at the Natural History Museum, London (NHMUK). This specimen consists of a partial rostrum (snout) and mandible, fragmentary ribs, and a complete right humerus (upper-arm bone).[3][4]
