新东方英语背诵美文50篇 第十三篇 A Rare Fossil Record
A Rare Fossil Record
The preservation of embryos and juveniles is a rate occurrence in the fossil record. The tiny, delicate skeletons are usually scattered by scavengers or destroyed by weathering before they can be fossilized. Ichthyosaurs had a higher chance of being preserved than did terrestrial creatures because, as marine animals, they tended to live in environments less subject to erosion. Still, their fossilization required a suite of factors: a slow rate of decay of soft tissues, little scavenging by other animals, 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 deposited about 190 million years ago. Over the years, thousands of specimens of marine reptiles, fish and invertebrates have been recovered from these rocks. The quality of preservation is outstanding, but what is even more impressive is the number of ichthyosaur fossils containing preserved embryos. Ichthyosaurs with embryos have been reported from 6 different levels of the shale in a small area around Holzmaden, suggesting that a specific 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 already well formed. One specimen is even preserved in the birth canal. In addition, the shale contains the remains of many newborns that are between 20 and 30 inches long.
新东方英语背诵美文50篇 | |
- 新东方英语背诵美文30篇 第一篇 Youth 青春
- 新东方英语背诵美文30篇 第二篇 Three Days to See(Excerpts) 假如给我三天光明
- 新东方英语背诵美文30篇 第三篇 Companionship of Books 以书为伴
- 新东方英语背诵美文30篇 第五篇 Ambition 抱负
- 新东方英语背诵美文30篇 第四篇 If I Rest, I Rust 如果我休息,我就会生锈
- 新东方英语背诵美文30篇 第六篇 What I have Lived for 我为何而生
- 新东方英语背诵美文30篇 第七篇 When Love Beckons You 爱的召唤
- 新东方英语背诵美文30篇 第八篇 The Road to Success 成功之道
- 新东方英语背诵美文30篇 第九篇 On Meeting the Celebrated 论见名人
- 新东方英语背诵美文30篇 第十篇 The 50-Percent Theory of Life 生活理论半对半