page_title: Acamptonectes
section_title: Palaeobiology
hierarchical_section_title: Acamptonectes / Palaeobiology
caption_attribution_description: Forefin of Acamptonectes densus. A–D: right humerus of NBM1284-R, in dorsal view (A), proximal view (B), distal view (C), and posterior view (D). E,F: right humerus of GLAHM 132588 (holotype), in ventral view with the associated ulna (E) and in distal view (F). The arrow points at the concave and edge-like posterior surface of the ulna, diagnostic of ophthalmosaurine ophthalmosaurs. G: proximal phalange of GLAHM 132588 (holotype). Abbreviations: aae facet: facet for the anterior accessory element; dpc: deltopectoral crest; td: trochanter dorsalis.
context_page_description: Acamptonectes is an extinct genus of ophthalmosaurid ichthyosaur that lived between 134 and 132 million years ago during the Early Cretaceous. Known from fossil deposits in England and Germany, the genus currently contains the single species A. densus, which was first described in 2012. Its discovery was important in the research of ichthyosaurs, as being one of the first known ophthalmosaurines from the Early Cretaceous, it provided evidence that no mass extinction of ichthyosaurs occurred during the Jurasic-Cretaceous boundary as previously understood. Nevertheless, Acamptonectes remains one of only eight genera of ichthyosaurs known during the Cretaceous. In life, Acamptonectes was probably a generalist predator. Its teeth were slender and textured with longitudinal ridges, which were best adapted for impaling prey; as a result, Acamptonectes likely fed on soft, fleshier prey such as fish and squid. The ichthyosaur's body was rigid and compact, which was suited for swimming at high speeds in tuna-like locomotion.
context_section_description: With their dolphin-like bodies, ichthyosaurs were better adapted to an aquatic environment than any other group of marine reptiles. They were viviparous (gave birth to live young) and likely incapable of leaving the water. As homeotherms with high metabolic rates, ichthyosaurs would have been active swimmers. Jurassic and Cretaceous ichthyosaurs, including Acamptonectes, had evolved thunniform (tuna-like) swimming, as opposed to the anguilliform (undulating) mode of locomotion employed by earlier species. Thunniform ichthyosaurs were able to swim faster and more efficiently than other marine reptiles of similar sizes, and better adapted to a pelagic lifestyle. This method of swimming was aided by their more compact bodies and crescent-shaped caudal fins. 
  Most of the skeleton of Acamptonectes appears to have been unusually rigid, which would have in effect severely limited the amount of side-to-side motion possible in the front part of the skeleton. Its snout was also shallower than in related species, and its ribs were more rounded in cross-section, which may have been a further adaptation to increase the stiffness of the animal's body, as they were likely more resistant to bending, according to the palaeontologist Darren Naish, one of the describers. The tightly packed occipital bones and cervical vertebrae would have allowed little movement in the neck, indicating it must have "shot through the water like a dart", according to palaeontologist Ulrich Joger, one of the describers.
caption: Forefin elements of NBM1284-R (A–D) and the holotype (E–G)
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