恐龙(dinosaur)
中生代大部分时期在陆地上占优势的一大批爬虫类，於中生代结束时灭绝。不同的时间有不同的种出现，且不会重叠。多为食肉动物，少数为草食性。恐龙分为蜥臀类和鸟臀类，两者的区别主要在於腰带的构造不同。多数恐龙具长尾，但长尾总是向後伸出并离开地面以保持平衡，而非像以前设想的那样拖在地面。多数种属卵生，有的还是温血动物。每个大陆都有发掘出恐龙化石。在白垩纪末以前，多数类型的恐龙一直很繁盛。在以後的一百万年间，恐龙完全从地质记录中消失了。造成它们大批绝灭的一个广泛接受的说法是白垩纪末地球上出现造山运动的地质周期，恐龙繁盛的低地减少，世界气候也发生变化，恐龙赖以为生的植物也发生演化性改变。另一理论是︰一颗天体与地球碰撞，产生大量尘埃，使地球处於一片黑暗之中，黑暗持续三年之久。因阳光不能照射大地，光合作用实际上难以进行，食物链的中断使恐龙及许多其他生物体死亡。许多人认为鸟类是当时存活下来的恐龙的後代。亦请参阅carnosaur、sauropod。
English version：
dinosaur
Any of the extinct reptiles that were the dominant land animals during most of the Mesozoic era (248-65 million years ago). The various species appeared at different times, and not all overlapped. Many were carnivores, but several were herbivores. Dinosaurs are classified as either ornithischians or saurischians, based on pelvic girdle structure. Most had a long tail, which they held straight out, apparently to maintain balance. Most species were egg layers. Some were probably warm-blooded. Dinosaur fossils have been found on every continent. Most types of dinosaur flourished until late in the Cretaceous period (65 million years ago), then disappeared within the next million years. Two theories for the cause of this mass extinction, following some 140 million years of existence, are that mountain-building cycles altered habitat and changed climate or that an asteroid hit the earth, resulting in immense dust clouds that blocked sunlight for several years. The birds are thought by many to be living descendants of the dinosaurs. See also carnosaur, sauropod.
