The name ichthyosaur means fish-lizard. They were ocean-dwelling reptiles. Their appearance is that of a cross between a dolphin and a fish. They had a dolphin-like head with a long toothed snout, a body similar to a dolphin, but with a shark-like dorsal fin and tail. Ichthyosaurs were swift predators well-adapted to hunting fish, cephalopods and other shell fish. This animal first appeared in the Mid-Triassic about 230 MYA, and died out in the Mid-Cretaceous about 90 MYA.

Stenopterygius lived during the Early Jurassic Period. Some contemporaries from this same locality include Steneosaurus bollensis, a marine crocodile, and Dorygnathus bathensis, a flying reptile.  The Plesiosaurus cf. dolichodeirus is very similar to the plesiosaurs that would have lived with this animal. Ammonites, fishes and crinoids would have helped to fill their watery home.