什麼是恐龍

中生代大部分時期在陸地上佔優勢的一大批爬蟲類，於中生代結束時滅絕。不同的時間有不同的種出現，且不會重疊。多爲食肉動物，少數爲草食性。恐龍分爲蜥臀類和鳥臀類，兩者的區別主要在於腰帶的構造不同。多數恐龍具長尾，但長尾總是向後伸出並離開地面以保持平衡，而非像以前設想的那樣拖在地面。多數種屬卵生，有的還是溫血動物。每個大陸都有發掘出恐龍化石。在白堊紀末以前，多數類型的恐龍一直很繁盛。在以後的一百萬年間，恐龍完全從地質記錄中消失了。造成它們大批絕滅的一個廣泛接受的說法是白堊紀末地球上出現造山運動的地質週期，恐龍繁盛的低地減少，世界氣候也發生變化，恐龍賴以爲生的植物也發生演化性改變。另一理論是︰一顆天體與地球碰撞，產生大量塵埃，使地球處於一片黑暗之中，黑暗持續三年之久。因陽光不能照射大地，光合作用實際上難以進行，食物鏈的中斷使恐龍及許多其他生物體死亡。許多人認爲鳥類是當時存活下來的恐龍的後代。亦請參閱carnosaur、sauropod。

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.