原帖由 痴渔童叟 于 2007-7-17 00:51 发表 
三叶虫化石,燕子石,也叫蝙蝠石,学名叫三叶虫化石。三叶虫(TRILONITES),属古生节肢动物,属三叶虫纲,生于海底,其种类繁多,大小不一,从一厘米至一米,生于寒武纪(6亿年)至奥陶纪(4.5亿年)最盛,“三 ... Sharks (superorder Selachimorpha) are fish with a full cartilaginous skeleton[1] and a streamlined body. They respire with the use of five to seven gill slits. Sharks have a covering of dermal denticles to protect their skin from damage and parasites and to improve fluid dynamics.[1] They have replaceable teeth. They are some of the world's most misunderstood predators, as they very rarely attack humans unless intimidated.
Sharks include species from the hand-sized pygmy shark, Euprotomicrus bispinatus, a deep sea species of only 22 centimetres (9 inches) in length, to the whale shark, Rhincodon typus, the largest fish, which grows to a length of approximately 12 metres (41 feet) and which, like the great whales, feeds only on plankton through filter feeding. The bull shark, Carcharhinus leucas, is the best known of several species to swim in both salt and fresh water (it is found in Lake Nicaragua, in Central America) and in deltas.[2
[ 本帖最后由 刘明远 于 2007-7-17 10:56 编辑 ] |