翼龙（希腊语意为："航行的蜥蜴 "或 "鳍蜥"）是海洋爬行动物的一个亚目，生活在侏罗纪和白垩纪时期，从大约2亿年前（Thalassiodracon）到大约8500万年前消亡。 翼龙的长度从4到15米（13-50英尺），是食肉动物，主要吃鱼，但也可能吃鱼龙和其他翼龙。 翼龙是翼龙目的两个亚目之一，与它们的近亲，较著名的翼龙一起。

翼龙是一种细长的动物，但比它们的亲戚双脊龙更粗壮，而且脖子很短。 翼龙没有像双脊龙那样长颈短头，而是长头短颈，更像鳄鱼。 最大的翼龙的头有2米（6.5英尺）长。 与一些双脊龙不同，翼龙大多饲养小鱼，翼龙似乎高度适应大型猎物。 最大的翼龙有10英尺（3米）的下颚和黄瓜大小的牙齿，可以一口吞下一头牛--或几个人。

Some two dozen species of pliosaur fossils have been dug up, with notable samples located in China, Argentina, England, Alaska, and Antarctica. A complete pliosaur skeleton was not found until an Antarctic dig in 2006. Parts of an earlier skeleton found by the same Oslo team, dubbed "The Monster" or "the T. rex of the Seas," is among the largest marine reptiles yet found, with a length of 15.25 m (50 ft). Although it is mistakenly called the largest marine reptile yet found, it is exceeded in size by members of several mosasaur lineages, including Mosasaurus hoffmanni and Hainosaurus bernardi (17 m/55 ft), and a species of plesiosaur found in Mexico nicknamed the Monster of "Aramberri" (around 15 m long). The Aramberri find was initially incorrectly identified as a pliosaur, and the size was exaggerated to 18 m or larger.

一些著名的liosaur属包括Pliosaurus, Peloneustes, Macroplata, Kronosaurus, Pliosaurus, Peloneustes, and Liopleurodon. pliosaurs的分布显然是全球性的或接近全球性的。 pliosaurs与plesiosaurs, ichthyosaurs, sharks, and mosasaurs一起生活在海洋的时间，有时被称为生命史上最危险的海洋。