中龙目（学名：Mesosauria）是一群已灭绝的爬行动物。牠们生活在大约2.99亿到2.8亿年前的早二叠纪。牠们是最早的水栖爬行动物之一，在陆地上演化过后再度返回水中。

最有名的中龙目就是中龙本身。中龙类的化石已在纳米比亚、巴西、乌拉圭、巴拉圭发现。中龙类被推测生活在淡水，不能横渡数千公里的大西洋。在巴西和南非发现中龙类的化石，证明非洲和南美原先曾是连接在一起的一个大陆。牠们的分布因此被看作是板块运动的一个证明。

中龙的外观类似短吻鳄，虽然最常见的标本只有40公分长。但是，最大的标本几乎有2公尺长，中龙可能是那个时代的最大型海生爬行动物。中龙被认为以鱼类或甲壳类为食，而且使用牙齿来滤水中的食物，类似现代的鲸。

Mesosaurs ("middle lizards") were a group of small aquatic reptiles that lived during the early Permian period, roughly 299 to 270 million years ago. Mesosaurs were the known first aquatic reptiles, having apparently returned to an aquatic lifestyle from more terrestrial ancestors. However, just how terrestrial mesosaur ancestors had become remains uncertain; recent research cannot establish with confidence if the first amniotes were fully terrestrial, or only amphibious. Most authors consider mesosaurs to have been aquatic, although at least some of them may have been amphibious, rather than completely aquatic, as indicated by their moderate skeletal adaptations to an aquatic lifestyle. They have long been thought to have been coastal forms that probably inhabited relatively shallow water, but recent research suggests that at least those from Uruguay inhabited a hypersaline environment, rather than a coastal marine environment. Recently described embryos show that pachyostosis of the ribs (which were thicker and denser than in terrestrial tetrapods) developed even before hatching, which suggests that mesosaurs were able to swim at birth, or shortly thereafter. They were apparently not very fast swimmers, with an optimal swimming speed estimated to have been between 0.15 and 0.86 m/s, but this must have been somewhat faster than the speed of their main prey, the pygocephalomorph crustaceans. Their reproductive mode is somewhat uncertain because association between adults and possible embryos in utero suggests viviparity, as in many aquatic reptiles, but a potentially isolated egg has also been found. Similarly, their affinities are uncertain; they may be either the most basal sauropsids, or among the most basal parareptiles.