Rancho La Brea – aeas精读 (Y10-12)
Prehistoric mammoths have been preserved in the famous tar pits of Rancho La Brea (Brea is the Spanish word for tar) in what is now the heart of Los Angeles, California. These tar pits have been known for centuries and were formerly mined for their natural asphalt, a black or brown petroleum-like substance. Thousands of tons were extracted before 1875, when it was first noticed that the tar contained fossil remains. Major excavations were undertaken that established the significance of this remarkable site. The tar pits were found to contain the remains of scores of species of animals from the last 30,000 years of the Ice Age.
Since then, over 100 tons of fossils, 1.5 million from vertebrates, 2.5 million from invertebrates, have been recovered, often in densely concentrated and tangled masses. The creatures found range from insects and birds to giant ground sloth’s, but a total of 17 proboscides (animals with a proboscis or long nose) — including mastodons and Columbian mammoths — have been recovered, most of them from Pit 9, the deepest bone-bearing deposit, which was excavated in 1914. Most of the fossils date to between 40,000 and 10,000 years ago.
The asphalt at La Brea seeps to the surface, especially in the summer, and forms shallow puddles that would often have been concealed by leaves and dust. Unwary animals would become trapped on these thin sheets of liquid asphalt, which are extremely sticky in warm weather. Stuck, the unfortunate beasts would die of exhaustion and hunger or fall prey to predators that often also became stuck.
As the animals decayed, more scavengers would be attracted and caught in their turn. Carnivores greatly outnumber herbivores in the collection: for every large herbivore, there is one saber-tooth cat, a coyote, and four wolves. The fact that some bones are heavily weathered shows that some bodies remained above the surface for weeks or months. Bacteria in the asphalt would have consumed some of the tissues other than bones, and the asphalt itself would dissolve what was left, at the same time impregnating and beautifully preserving the saturated bones, rendering them dark brown and shiny.
在加利福尼亚州洛杉矶市中心，Rancho La Brea（Brea是西班牙语中的焦油）的着名焦油坑中保存着史前猛犸象。几个世纪以来，这些焦油坑已为人所知，以前因天然沥青，黑色或棕色石油类物质而开采。在1875年之前提取了数千吨，当时它首次发现焦油中含有化石残留物。进行了大量挖掘，确定了这一显着遗址的重要性。发现焦油坑包含了冰河时代最后30，000年的几十种动物的遗骸。 从那时起，已经发现了超过100吨的化石，150万来自脊椎动物，250万来自无脊椎动物，通常是密集和纠结的群众。发现的生物范围从昆虫和鸟类到巨型地面树懒，但总共有17种长鼻虫（长鼻动物或长鼻子） - 包括乳齿象和哥伦比亚猛犸象 - 已经被发现，其中大多数来自最深的骨头9号坑 - 轴承矿床，于1914年被挖掘出来。大多数化石可以追溯到4万至1万年前。 La Brea的沥青渗入地表，特别是在夏季，形成浅水坑，通常被树叶和灰尘掩盖。不小心的动物会被困在这些薄薄的液体沥青上，这些沥青在温暖的天气里非常粘。不幸的是，这些不幸的野兽会因疲惫和饥饿而死，或者成为掠食者的牺牲品。 随着动物腐烂，更多的拾荒者会被吸引并被轮到他们。食肉动物的数量大大超过了食草动物的集合：对于每个大型食草动物，都有一只剑齿猫，一只土狼和四只狼。一些骨头严重风化的事实表明，一些尸体仍然在地表之上数周或数月。沥青中的细菌会消耗除骨头之外的一些组织，沥青本身会溶解剩下的组织，同时浸渍并精美地保留饱和的骨骼，使其呈现深褐色和有光泽。