Lariosaurus was the smallest of the nothosaurs.

Although small by nothosaur standards,‭ ‬Lariosauru remains one of the most important nothosaurs known to palaeontology as remains are so well preserved they contain the presence of juvenile Lariosaurus,‭ ‬as well as what they ate.‭ ‬The juvenile specimens inside an adult Lariosaurus are very well preserved suggesting that they were not chewed or eaten,‭ ‬and that Lariosaurus were possibly not cannibalistic.‭ ‬As such if the popular theory of them being young waiting to be born is correct,‭ ‬then it proves that the marine reptiles had developed the ability to give birth to live young before they were completely restricted to aquatic life.‭ ‬This has long been suspected for later and larger marine reptiles likeichthyosaurs,‭ ‬plesiosaurs,‭ ‬and mosasaurs as terrestrial movement would have been impossible for these reptiles.While nothosaurs in general are thought to have eaten fish,‭ ‬Lariosaurus is confirmed to have eaten other marine reptiles,‭ ‬specifically placodonts as indicated by the remains of two Cyamodus juveniles inside one Lariosaurus skeleton.
        Lariosaurus also seems to be a marine reptile in transition to a more aquatic life.‭ ‬This is because while the rear legs were still suited to land movement,‭ ‬the front legs had evolved to form‭ ‬paddles.‭ ‬This would be a hindrance to movement on land,‭ ‬but a considerable bonus when swimming in the water.