"Ichthyopterygia ("fish flippers") was a designation introduced by Sir Richard Owen in 1840 to designate the Jurassic ichthyosaurs that were known at the time, but the ...
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term is now used more often for both true Ichthyosauria and their more primitive early and middle Triassic ancestors.
Basal ichthyopterygians (prior to and ancestral to true Ichthyosauria) were mostly small (a meter or less in length) with elongated bodies and long, spool-shaped vertebrae, indicating that they swam in a sinuous, eel-like manner. This allowed for quick movements and maneuverability that were advantages in shallow-water hunting. Even at this early stage, they were already very specialised animals with proper flippers, and would have been incapable of movement on land." - (Wikipedia (en) 05.03.2020)
