飞    向    蓝    天    的    恐    龙   

 说    到    恐    龙   , 人    们    往    往    想    到    凶    猛    的    霸    王    龙    或    者    笨    重   、 迟    钝    的    马    门    溪    龙   ; 谈    起    鸟    类   , 我    们    头    脑    中    自    然    会    浮    现    轻    灵    的    鸽    子    或    者    五    彩    斑    斓    的    孔    雀   。 二    者    似    乎    毫    不    相    干   , 但    近    年    来    发    现    的    大    量    化    石    显    示   : 在    中    生    代    时    期   , 恐    龙    的    一    支    经    过    漫    长    的    演    化   , 最    终    变    成    了    凌    空    翱    翔    的    鸟    儿   
 早    在    世    纪   , 英    国    学    者    赫    胥    黎    就    注    意    到    恐    龙    和    鸟    类    在    骨    骼    结    构    上    有    许    多    相    似    之    处   。 在    研    究    了    大    量    恐    龙    和    鸟    类    化    石    之    后   , 科    学    家    们    提    出   , 鸟    类    不    仅    和    恐    龙    有    亲    缘    关    系   , 而    且    很    可    能    就    是    一    种    小    型    恐    龙    的    后    裔   。 根    据    这    一    假    说   , 一    些    与    鸟    类    亲    缘    关    系    较    近    的    恐    龙    应    该    长    有    羽    毛   , 但    一    直    没    有    找    到    化    石    证    据   。 世    纪    末    期   , 我    国    科    学    家    在    辽    宁    西    部    首    次    发   
 现    了    保    存    有    羽    毛    的    恐    龙    化    石   , 顿    时    使    全    世    界    的    研    究    者    们    欣    喜    若    狂   。 辽    西    的    发    现    向    世    人    展    示    了    恐    龙    长    羽    毛    的    证    据   , 给     这    幅    古    生    物    学    家    们    描    绘    的    画    卷    涂    上    了    点    睛    之    笔   
 恐    龙    是    如    何    飞    向    蓝    天    的    呢   ?  让    我    们    穿    越    时    空    隧    道   ,  访    问    中    生    代    的    地    球   ,  看    看    这    一    演    化    过    程    吧   !
 地    球    上    的    第    一    种    恐    龙    大    约    出    现    在    两    亿    四    千    万    年    前   。 它    和    狗    一    般    大    小   , 两    条    后    腿    粗    壮    有    力   , 能    够    支    撑    起    整    个    身    体   。 数    千    万    年    后   , 它    的    后    代    繁    衍    成    一    个    形    态    各    异    的    庞    大    家    族   。 有    些    恐    龙    像    它    们    的    祖    先    一    样    用    两    足    奔    跑   , 有    些    恐    龙    则    用    四    足    行    走   。 有    些    恐    龙    身    长    几    十    米   , 重    达    数    十    吨   ; 有    些    恐    龙    则    身    材    小    巧   , 体    重    只    有    几    千    克   。 有    些    恐    龙    凶    猛    异    常   , 是    茹    毛    饮    血    的    食    肉    动    物   ; 有    些    恐    龙    则    温    顺    可    爱   , 以    植    物    为    食   。 其    中   , 一    些    猎    食    性    恐    龙    的    身    体    逐    渐    变    小   , 越    来    越    像    鸟    类   : 骨    骼    中    空   , 身    体    轻    盈   ; 脑    颅    膨    大   , 行    动    敏    捷   ; 前    肢    越    来    越    长   ,
 能    像    鸟    翼    一    样    拍    打   ; 体    表    长    出    美    丽    的    羽    毛   , 不    再    披    着    鳞    片    或    鳞    甲   。 它    们    中    的    一    些    种    类    可    能    为    了    躲    避    敌    害    或    寻    找    食    物    而    转    移    到    树    上    生    存   。 这    些    树    栖    的    恐    龙    在    树    木    之    间    跳    跃   , 降    落   , 慢    慢    具    备    了    滑    翔    能    力   , 并    最    终    能    够    主    动    飞    行   。 不    过   , 另    一    种    看    法    是   , 飞    行    并    非    始    于    树    栖    生    活   。 有    些    科    学    家    推    测   , 一    种    生    活    在    地    面    上    的    带    羽    毛    的    恐    龙   , 在    奔    跑    过    程    中    学    会    了    飞    翔   。 不    管    怎    样   , 科    学    家    们    认    为   : 原    本    不    会    飞    的    恐    龙    最    终    变    成    了    天    之    骄    子   —— 鸟    类   , 它    们    飞    向    了    蓝    天   , 从    此    开    辟    了     的    生    活    天    地   
 亿    万    年    前   , 一    种    带    羽    毛    的    恐    龙    脱    离    同    类   , 飞    向    蓝    天   , 演    化    出    今    天    的    鸟    类    大    家    族   。 科    学    家    们    希    望    能    够    全    面    揭    示    这    一    历    史    进    程   。 随    着    越    来    越    多    相    关    化    石    的    发    现   , 他    们    离    这    一    愿    望    的    实    现    已    越    来    越    近    了   
 钝    仅    描    隧    衍    吨    颅    膨    捷    栖    辟    崭   

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