The prehistoric Oceans

　　During the Mesozoic era (which includes the Traissic, the Jurassis, and the Cretaceous periods), world's oceans were home[1] to many large marine reptiles. Some of these creatures are familiar to us today, like the crocodiles and turtles. Others, like Ichthyosaurus (fish lizard), look similar[2] to dolphins, but were reptiles not mammals. Marine reptiles were a very important part of the Mesozoic oceans, but they were not the only creatures to live in them. Some of the most familiar and plentiful fossils, such as the ammonites, lived in the seas at that time.

Snake stones
　　Ammonites were molluscs (animals with a shell), distantly related to snails and shellfish. They floated in the water, catching food with their tentacles. When people first found these coiled fossils, they thought that they were snakes that had been turned to stone.

Pliosaur
　　Pliosaurs had very short necks, and skulls more adapted to kill larger animals, possibly even ichthyosaurs and plesiosaurs.

Lchthyosaur
　　Lchthyosaurs were dolphinlike reptiles that grew up to 50 feet in length.

Plesiosaurs
　　Plesiosaurs had long necks that they used to snatch small fish from the water.

史前海洋世界

　　在中生代时期（包括三叠期、侏罗纪、白垩纪），世界上的海洋曾经是许多大体积海洋爬行动物的家。它们中的某些动物我们至今依然熟悉，如鳄鱼和海龟。其他动物，比如鱼龙看似海豚，实际上不是哺乳类，而是爬行类。海洋爬行动物是中生代海洋的重要组成部分，但它们不是唯一栖身海洋的生物。有些我们最熟悉的和发现最多的动物化石，如菊石等，当时都生活在海洋里。

蛇石
　　蛇石（即菊石）是软体动物（带壳的动物），与蜗牛和甲壳类动物略有关系。它们在水中飘游，用触须捕捉食物。人们第一次发现这些盘绕化石时，认为是由蛇变成的。

上龙
　　上龙颈部很短，它们的头骨更适于将大型动物如鱼龙和蛇颈龙致于死地。

鱼龙
　　鱼龙是形似海豚的爬行动物，身长可达50英尺。

蛇颈龙
　　蛇颈龙有长颈，用来捕捉水中的小鱼。