VOA常速英语2016--哺乳动物 脑部越大 嗅觉越灵？（在线收听）

哺乳动物 脑部越大 嗅觉越灵？

Researchers used computed tomography or CT scans to analyze the skulls of 190-million-year-old mammals found in a Jurassic-era fossil bed in China. These tiny critters, co-existed with thegiant, meat-eating dinosaurs and probably survived by being nocturnal. But to be active in thenight, to be nocturnal, you really have to have "very special sensory adaptations. Zhe-Xi Luo isa paleontologist at the Carnegie Museum of Natural History in Pittsburgh, Pennsylvania, and amember of the research team that studied the prehistoric mammal skulls. He says the CT-scans helped the team construct a virtual brain case for two of the ancient mammals. In thisstudy we have found that the large brain is becoming larger primarily because the olfactory, orthe smelling part of the brain, become very big and also the part related to skin tactilesensation also becomes big. Luo says the acute sense of smell and touch that helpedmammals survive among the predatory dinosaurs is clearly visible in their ancient anatomy. Sothe new evolutionary biology idea from this study of fossils is, maybe, a capacity to smell verywell is as important, even more important than hearing and that the tactile sense probablyplayed a big role too. The study finds that the Jurassic-era mammals - including the tinyHadrocodium, whose skull was smaller than a paper clip - had brains that were two or threetimes larger than any mammal relatives before them. Hadrocodium has this big head, smallmammal, relative to the body size, it has already achieved about the same range of brain sizeas modern mammals. Luo says he was thrilled to see this impressive brain development in our190-million-year-old mammalian relatives. An important evolutionary milestone that helpedmake mammals - and humans among them - one of the Earth's dominant animal classes.

研究人员用计算机断层扫描（CT）来分析在侏罗纪化石层发现的有1.9亿年历史的2只哺乳动物头骨化石。这些小生物与体型巨大的食肉恐龙共同生活在侏罗纪时代，据推测这些小生物可能是通过在夜间活动逃过一劫的。

但要在夜间活动，就必须要有“非常特别的感官适应力”。罗哲希是宾夕法尼亚州匹兹堡市卡内基自然历史博物馆的古生物学者，同时也是史前哺乳动物头骨研究组的成员。他说，CT扫描可以帮助研究组对古代哺乳动物的大脑进行建模分析。研究中，我们发现，这两只哺乳动物的头部较大主要是因为它们大脑中的嗅觉部位和触觉部位比较大。罗还表示，这些哺乳动物灵敏的嗅觉和触觉让他们成功躲过了恐龙的捕食，这一点在他们的解剖中很明显。所以，这个研究得出了一个有关生物进化的新观点，就是：可能灵敏的嗅觉，甚至要比听觉更重要。同时，触觉也很重要。研究发现，这两只哺乳动物中有一只体型小巧的吴氏巨颅兽，其头骨比回形针还要小，但脑部比过往时期的祖先大两三倍。跟其体型相比，吴氏巨颅兽的脑部比较大，程度甚至可以与现代哺乳动物的脑部大小差不多。罗说，在这两只哺乳动物身上发现的脑部进化，着实让人震惊。也正是这一里程碑式的进化成就了今天的很多哺乳动物，其中包括处于主导地位的人类。