冷水生物群

COLD WATER BIOTA

居住在年平均溫度通常接近0℃的冷水體的一群生物，稱為冷水生物群。通常這樣的冷水體存在於極區的海洋及任何海洋之深處（約超過2000公尺）。所以冷水 生物群又可再細分為極區冷水生物群及深海冷水生物群二類。二者均具有指示低溫之意義存在。在地質記錄中，極區一定靠近高緯度，所以極區冷水生物群比深海冷 水生物群，易於辨認。
在地質記錄中之深海冷水生物群依「均變說」之原理，可嘗試利用其現生代表種之有關知識，逆推出化石種之生活習性及環境而加以確認。但是極區冷水生物群除了 藉助於「均變說」外，亦可利用重建古生物地理之方法來確認。一般古生物地理之重建則基於(1)大規模之形態變化梯度，像有孔蟲之左、右弦之比例，腹足類之 殼頂的特徵及珊瑚之生長速率。(2)大規模之多樣變化梯度，此取決於一個樣本中有多少相異種類(3)大規模之地化變化梯度，像同位素之比及礦物成分變異 等，及(4)生物之相似性，此取決於生物成員之出現或不出現，以便計算出相似程度之高低。

A cold water biota is here defined as organisms living in water with an annual mean temperature of nearly 0℃. Since such cold water is present in both the polar oceans and deep seas (approximatel 2000 meters in depth)， both polar cold water biota and deep sea cold water biota are differentiated. Either biota can be used as an indicator of low temperature. In the geological record， owing to its remarkable latitudianal dependence， the polar cold water biota may be more easily recognized than the deep sea cold biota. The recognition of deep sea cold water biota is approached by unifqrmitarianism in that we can infer the environment and mode of life of fossils from the knowledge of living representatives. However the polar cold water biota can be recognized either by a uniformitarian approach or by a palepbiogeographic approach. The reconstruction of palepbiogography is based on (1) Large scale morphological gradients， including the coiling directional ratio of foraminifers， the apical features of gastropods and growth rate of corals， (2) Large scale diversity gradients which utilize the absolute number of taxa in each sample， (3) Large scale geochemical gradients， including isotope ratios and differences of mineralogical composition， and (4) Biotic similarity which involves the degree of resemblance of biotic content according to the presence and absence of taxa.