英语科普小知识 五百万年前地球上存在14种鳄鱼

海量资料下载 免费学习英语 www.englishvip.com/xinlw.htm （申请网址） Today, the most diverse species of crocodile are found in northern South America and Southeast Asia: As many as six species of alligator（短吻鳄） and four true crocodiles exist, although no more than two or three ever live alongside one another at the same time. It was a different story nine to about five million years ago, however, when a total of 14 different crocodile species existed and at least seven of them occupied the same area at the same time, as an international team headed by paleontologists Marcelo Sánchez and Torsten Scheyer from the University of Zurich is now able to reveal. The deltas of the Amazonas and the Urumaco, a river on the Gulf of Venezuela that no longer exists, boasted an abundance of extremely diverse, highly specialized species of crocodile that has remained unparalleled ever since.   Two new fossil crocodile species discovered   While studying the wealth of fossil crocodiles from the Miocene in the Urumaco region, the scientists discovered two new crocodile species: the Globidentosuchus brachyrostris, which belonged to the caiman（凯门鳄） family and had spherical（球形的） teeth, and Crocodylus falconensis, a crocodile that the researchers assume grew to well over four meters long. As Sánchez and his team reveal, Venezuela's fossils include all the families of crocodile species that still exist all over the world today: the Crocodylidae, the so-called true crocodiles; the Alligatoridae, which, besides the true alligators, also include caimans; and the Gavialidae, which are characterized by their extremely long, thin snouts and are only found in Southeast Asia nowadays.   On account of the species' extremely different jaw shapes, the researchers are convinced that the different crocodilians were highly specialized feeders: With their pointed, slender snouts, the fossil gharials must have preyed on fish. "Gharials occupied the niche in the habitat that was filled by dolphins after they became extinct," Sánchez suspects. With its spherical teeth, however, Globidentosuchus brachyrostris most likely specialized in shellfish, snails or crabs. And giant crocodiles, which grew up to 12 meters long, fed on turtles, giant rodents and smaller crocodiles. "There were no predators back then in South America that could have hunted the three-meter-long turtles or giant rodents. Giant crocodiles occupied this very niche," explains Scheyer.   Andean uplift led to extinction   The unusual variety of species in the coastal and brackish（含盐的） water regions of Urumaco and Amazonas came to an end around 5 million years ago when all the crocodile species died out. The reason behind their extinction, however, was not temperature or climate changes -- temperatures in the Caribbean remained stable around the Miocene/Pliocene boundary. Instead, it was caused by a tectonic event: "The Andean uplift changed the courses of rivers. As a result, the Amazon River no longer drains into the Caribbean, but the considerably cooler Atlantic Ocean," explains Sánchez. With the destruction of the habitat, an entirely new fauna emerged that we know from the Orinoco and Amazon regions today. In the earlier Urumaco region, however, a very dry climate has prevailed ever since the Urumaco River dried up. 今天，最多样化的物种鳄鱼被发现在南美洲北部和东南亚：多达6种鳄鱼（短吻鳄）和四个真正的鳄鱼存在，但从来没有超过两个或三个在彼此一起生活同一时间。这是一个不同的故事九然而，大约500万年前，当存在一共有14种不同的鳄鱼品种，至少七人住在同一区域同时，为首的一个国际研究小组的古生物学家马塞洛·桑切斯和Torsten来自苏黎世大学的斯切尔现在能够揭示。三角洲亚马孙和Urumaco的，一条河上的海湾，委内瑞拉不再存在，吹嘘极其多样，高度专业化的物种鳄鱼，一直保持无与伦比自从丰富的。   两个新的化石发现鳄鱼品种   虽然研究中新世在Urumaco地区财富的鳄鱼化石，科学家发现了两个新的鳄鱼品种：的Globidentosuchus brachyrostris，属于凯门鳄（凯门鳄）的家庭和有球状（球形的）牙齿，鳄falconensis的，增长远远超过四米长的鳄鱼，研究人员假设。正如桑切斯和他的团队透露，委内瑞拉的化石包括所有的鳄鱼品种，仍然存在着所有世界各地的今天：鳄，所谓真正的鳄鱼; Alligatoridae，其中，除了真正的鳄鱼，也包括凯门鳄的家庭;和Gavialidae，他们极长，尖尖的嘴巴，其特点是，现今只分布于东南亚。   物种极为不同的下颌形状，研究人员相信，不同的鳄类是高度专业化的馈线：尖，细长的口鼻部，的化石gharials必须捕食鱼类。“Gharials占领利基充满海豚的栖息地，他们灭绝后，桑切斯怀疑。” 然而，随着其球形牙齿，Globidentosuchus brachyrostris最有可能专门从事贝类，蜗牛，螃蟹。喂养长大到12米长的巨型鳄鱼，海龟，巨型啮齿动物和小鳄鱼。斯切尔，“解释”有没有天敌然后在南美洲，三米长的海龟或巨型啮齿动物猎杀巨型鳄鱼占领这个利基。   安第斯山脉隆起导致灭绝   不寻常的品种种在沿海和苦咸水（含盐的）水Urumaco和亚马孙地区的大约5万年前走到了尽头时，所有的鳄鱼物种死亡。他们灭绝背后的原因，然而，是不是温度或气候变化-在加勒比地区的气温仍然稳定在中新世/上新世边界。相反，它是由构造事件引起的：“安第斯隆起改变河流的课程。因此，亚马逊河不再排入加勒比海，但相当凉爽的大西洋，”桑切斯说。随着栖息地的破坏，出现了一个全新的动物，我们知道，从今天的奥里诺科和亚马逊地区。然而，在早期Urumaco地区气候非常干燥自从盛行的Urumaco河干涸。 “成千上万人疯狂下载。。。。。。 更多价值连城的绝密英语学习资料， 洛基内部秘密英语，技巧，策略 请在 网上 申请报名” 洛基国际英语 竭诚为您服务