陳蕙雅思教材 - 雅思閱讀精選 (A Rare Fossil Record)

A Rare Fossil Record

The preservation ofembryos and juveniles is a rate occurrence in the

fossil record. The tiny,delicate skeletons           are usuallyscattered  by

scavengers or destroyedby weathering  before they can  be fossilized.  

Ichthyosaurs  had  a       higher chance  of  being preserved  than  did  

terrestrial creaturesbecause, as marine animals, they tended to live in          

environments less subjectto erosion. Still, their fossilization required  

a suite  of factors: a slow rate of  decay      of soft tissues, little

scavenging by otheranimals, a lack of swift currents and waves to jumble

and carry away        small bones,  and fairly  rapid  burial. Given  these

factors,  some areas  have  become a  treasury  of well-preserved          

ichthyosaur fossils.

The   deposits at  Holzmaden,  Germany, present   an   interesting case  

for  analysis. The ichthyosaur remains are found in           black,bituminous

marine shales depositedabout 190 million years ago. Over the years,

thousands of specimens of marine reptiles, fish and invertebrates havebeen

recovered from theserocks. The quality of preservation is     outstanding,but

what is even more   impressive  is   the   number  of   ichthyosaur  

fossils   containing  preserved   embryos.

Ichthyosaurs with embryoshave been reported from 6 different levels of the

shale in a small areaaround Holzmaden, suggesting that  aspecific site

was used  by large numbers  of ichthyosaurs repeatedly over time. The

embryos are  quite advanced in their physical development; their paddles,

for example, are alreadywell formed. One specimen is          evenpreserved in the

birth canal. In addition,the shale contains the remains of many newborns

that are between 20 and30 inches long.

Why are there so  many pregnant females and  young at Holzmaden when they

are so rare elsewhere?The quality of      preservation is almostunmatched and  

quarry operationshave  been carried out carefully  with an awareness of  

the      value of the fossils. But these factors donot account for the

interesting question ofhow there came to be such a     concentrationof

pregnant ichthyosaurs ina particular place very close to their time of

giving birth.

罕見的化石記錄  胚胎與幼體被保存下來在化石記錄中是少見的事情。微小纖細的骨骼 通常在石化前就被食腐肉的動物拆散了，或者被風化作用破壞掉了。  

魚龍比起陸地的動物 有更大的幾率被保存下來，因為它們作為海洋動物常生活在腐蝕性較小的環境中。  但是它

們的石化需要一系列因素：軟組織的腐爛速度緩慢，很少被其他動物殘食，缺少混雜、沖走 小骨頭的快速水流和波浪，以及相當快地被掩埋。  

當這些因素存在時，某些地區就會變成 一個充滿保存完好的魚龍化石的寶庫。在德國獲爾茲梅登，那兒的沉積物給人們提出了一個 有趣的分析案例。  

人們在黑色的、含瀝青的海洋葉岩中發現了約 19，000 年前沉積下來的 魚龍化石。  

幾年時間內，在這些岩石中取得了數以千計的海洋爬行動物、魚類以及無脊椎 動物的標本。  

它們的保存品質非常的好，但更令人稱奇的是保存下來的育有胚胎的魚龍化 石數目。  在獲爾茲梅登附近一個小地區的六個不同的葉岩層中分別發現了育有胚胎的魚龍

化石。 這表明大量的魚龍經年累月重複使用一個特定的地點。 那些胚胎已經發育得相當完 整了。  比如，它們的蹼槳已經完全形成了。  

有一個標本甚至被保存在產道中。  而且，那 塊葉岩包含著很多在 20 到 30 英寸之間的新生幼體的化石。為什麼在其他地方那麼稀少的懷

孕雌獸和幼體在獲爾茲梅登卻那麼多呢?  因為其保存品質幾乎舉世無雙，採集工作的進行一 直是一絲不苟的。  

大家都認識到這些化石的價值極其珍貴，但這些因素並不能解釋這個有 趣的問題：  為什麼在一個特定的地點會如此集中地出現即將臨產的懷孕魚龍群呢?