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现在我想就年龄问题

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请大家举个手

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或是鼓个掌

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我想知道

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在座有多少人的年龄介于3至12岁之间？

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（笑声）

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没有是吧？

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我知道了

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今天我要来讲一讲恐龙

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你还记得你小时候有多喜欢恐龙吗？

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（鼓掌）

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恐龙是种很有趣的东西

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（笑声）

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不过今天

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我们要从另一个角度来看待它们

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从恐龙身上我学到了一些东西

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那就是尽量别让自己灭绝了

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（笑声）

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就这么简单

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（笑声）

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人们常常问我

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事实上，我被问得最多的问题就是

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为什么小孩子都那么喜欢恐龙？

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恐龙到底有哪里特别吸引人？

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这时候我一般会这么回答

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因为恐龙很大，很与众不同

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而且它们灭绝了

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是的，所有恐龙都灭绝了

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虽然我也不能百分百肯定

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不过我们马上就要讲到重点了

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所以恐龙总体来说就是

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很大，很与众不同，而且已经灭亡

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我今天演讲的主题是：

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会“变形”的恐龙

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及它们过早灭亡的原因

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我们印象中的恐龙

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有大有小，形态各异

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有许多不同的种类

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很久以前

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大概是二十世纪初的时候

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各大博物馆都对恐龙很感兴趣

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他们四处搜集恐龙化石

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这个过程非常有趣

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因为每个博物馆都想要比别人更大更好的

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恐龙化石

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所以如果多伦多的博物馆

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找到一个大家伙——霸王龙

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那么渥太华的博物馆就一定要找到一个更大、更好的

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才肯罢休

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当时几乎所有博物馆都是这样

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所以所有人都在四处寻找

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大型的恐龙化石

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这是在上世纪初的时候

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到了1970年

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有些科学家就开始思考

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怎么回事

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看看我们找到的这些恐龙化石

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全都这么大

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那小恐龙去哪了？

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科学家们就开始思考这个问题

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针对这个问题做研究、写论文

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“小恐龙到哪里去了？”

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（笑声）

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你要是去博物馆就能发现

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那里根本就没有几个小恐龙

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人们假设——这也正是问题所在

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人们假设

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如果小恐龙、或者说幼年时期的恐龙

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真的存在的话

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应该很容易被辨别出来

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既然有大恐龙

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就应该有小恐龙

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但是我们现在看到的全是些大家伙

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这就让我们发现了几个问题

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首先，科学家都是很自负的

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他们都很喜欢给恐龙起名字

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他们喜欢给任何东西起名字

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所有人都想要一个自己亲自给起名的新动物

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（笑声）

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所以每当他们发现一个新物种看起来有一点点不一样

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他们就给它起一个新名字

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这样一来

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我们就有了一大堆不同名字的恐龙

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1975年

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有个人脑子里突然灵光一现

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这个人就是宾夕法尼亚大学的

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彼得·道森博士

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他意识到

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恐龙的发育过程

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其实和鸟类很相似

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而与爬行类动物

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却不怎么一样

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然后

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他拿食火鸡举了个例子

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食火鸡这种鸟很酷——事实上

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所有头上有冠的鸟都很酷

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因为它们直到

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发育到成年个体的百分之八十的时候

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头上的冠才会开始生长

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现在我们仔细想想

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它们实际上一直保持着幼年时期的特征

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直到发育过程的后期

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这种颅骨发育

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非常的迅速

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所以

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如果你看到一只

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发育到百分之八十的小食火鸡

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你也认不出来它是一只食火鸡

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你会觉得这是两种不同的动物

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这就是问题所在

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彼得·道森认识到了这一点

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于是他拿鸭嘴恐龙

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来举例说明

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他把幼年鸭嘴龙

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和成年鸭嘴龙放在一起比较

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如果它的生长

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是呈线性发展的

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那么幼年鸭嘴龙应该有一个

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差不多成年鸭嘴龙一半大小的顶冠

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但事实上

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百分之六十五即将成年的小鸭嘴龙

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都没有顶冠

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这就很有意思了

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看来这就是使人们的思维

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走入误区的地方

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我的意思是

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如果人们能接受并发展彼得·道森的发现

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我们现在所拥有的恐龙种类

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就会少得多

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但是别忘了，科学家都是很自负的

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而且特别喜欢给东西起名字

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所以当他们发现了与原先不一样的恐龙

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还是会不断地给它们取新名字

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现在我们有了一种方法

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可以测定一只恐龙，或是任何一种动物

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是幼年的还是成年的

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那就是切开它们的骨头进行分析

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但是你也能够想象

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要去切一只恐龙的骨头还是挺困难的

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因为在博物馆里

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这些骨头相当珍贵

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他们把每一块骨头

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都包着泡沫放进小罐子里

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保存得好好的

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如果你拿着锯子走进去说要切开这些骨头看看

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恐怕不会受到太多欢迎

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（笑声）

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所以一般情况下我们没这个机会

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但是我也有一个博物馆

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我也搜集恐龙化石

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而且我一点也不介意把这些骨头切开

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所以我就把它切开了

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（掌声）

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如果你切开小恐龙的骨头

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会发现里面空隙很大呈海绵状，如图A

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如果你切开老恐龙的骨头

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则会发现里面的骨质排列很紧密

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所以你知道这是一根已经发育成熟了的骨头

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这就很容易分清楚了

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现在

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我们来看看这个

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在北美洲，美国的北部平原

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和加拿大的阿尔伯塔及萨斯喀彻温省南部平原

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有一种叫做“地狱溪地层”的岩石群

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在那里发现了最晚生活在地球上的恐龙化石

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一共有12个

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我们可以看到

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这是12个已经灭绝了的

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恐龙化石

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我们现在就是要

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研究这些化石

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我的学生，还有其他工作人员

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我们一起把这些骨头切开

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你也知道

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切开一条恐龙的腿骨也就算了

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但是你要是去博物馆

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问他们：“你介不介意我把你们的

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恐龙头骨切开？”

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他们一定会说：“给我滚。”

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（笑声）

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所以，在这12个恐龙化石里

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我们先看看这三个

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这三个都属于厚头龙类

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大家都看得出来

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它们之间是有亲缘关系的

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人们普遍假设

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它们是堂兄弟

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或者这之类的关系

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但从来没有人想过

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它们的关系可能比这还要近得多

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换句话说

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人们看到的是它们之间的差异

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但是

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如果你想判断

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两个人之间是否有亲缘关系

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你肯定不会去看他们有多不同

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而是寻找他们的

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相同之处

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现在人们只注意到了

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这三种恐龙不同的地方

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厚头龙的颅顶大而厚

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脑后有一些小的突起

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鼻端也有不少瘤状物

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第二种恐龙——冥河龙

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和厚头龙生活在同一时期

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它的脑后有数根钉状尖刺

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颅顶很小

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鼻子上也有瘤状物

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第三种恐龙叫做龙王龙

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它还有一个名字叫做“霍格沃茨之眼”

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因为它和小说中描写的“龙”

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非常相似

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它脑后也有钉状的尖刺，鼻子上有瘤状物

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但没有颅顶

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没有人注意到这三种恐龙鼻子上的瘤状物非常相似

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他们一下子就下了结论：

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“这是三种不同的恐龙

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龙王龙应该是最原始的一种

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这种又应该比那种原始”

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我就不明白了

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他们是怎么看出来的呢？

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如果光从头骨来看的话

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把它们以大小顺序排成一列

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就成了这样

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龙王龙是最小的

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其次是冥河龙

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厚头龙最大

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这是不是应该

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给我们一点启示了？

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（笑声）

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但可惜他们都没发现

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我们也知道是为什么了

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因为科学家们最爱给东西起名字

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那么，如果我们把这些头骨切开的话

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龙王龙——

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我把我的龙王龙给切了——

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看！里面是海绵状的

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非常疏松

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这说明这是一只幼年的恐龙

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而且它长得很快

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会越长越大

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如果你切开冥河龙的骨头

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会发现也是一样

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它的颅顶虽小

245
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却发育得

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非常迅速

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最有意思的还是龙王龙脑袋后面的尖刺

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它也长得非常快

249
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而冥河龙脑后的刺

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却是在退化的

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也就是说它在颅顶变大的同时

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尖刺会越来越小

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我们再看厚头龙

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它的颅顶非常坚实

255
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而它脑后的突起

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也是在退化的

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所以，就光从这三种恐龙来看

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作为一个科学家

259
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我们很容易就能做出这样的假设：

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这是同一种动物的

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生长序列

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这样一来

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冥河龙和龙王龙

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就不得不“灭绝”了

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（笑声）

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好了

267
00:11:46,000 --> 00:11:49,000
现在我们还剩下

268
00:11:49,000 --> 00:11:53,000
10种恐龙要研究

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我和一个在伯克利的同事

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一起研究了三角龙

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我们发现在2000年前——

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我想想

273
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三角龙是在19世纪发现的

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但是在2000年之前

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从来没有人见过幼年的三角龙

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世界上几乎所有博物馆都有三角龙的化石

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就是没有一个小三角龙

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我们都知道为什么，是吧？

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因为大家都想要大的

280
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所以每家博物馆都有一个大的

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我和我的同事在外面搜索了一圈

282
00:12:26,000 --> 00:12:28,000
结果发现了许多小三角龙

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它们到处都是

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所以现在我们的博物馆里收藏了一大堆小三角龙

285
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（笑声）

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00:12:39,000 --> 00:12:41,000
大家都说这是因为我有一个小博物馆

287
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小博物馆里自然是小恐龙

288
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（笑声）

289
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仔细观察一下三角龙

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你能看到它在变化、在“变形”

291
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在小三角龙长大的过程中

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它们的角是向后弯曲的

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但当它们长大之后

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角却变成了向前弯曲

295
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这是不是很酷？

296
00:13:01,000 --> 00:13:03,000
我们再看看它头盾的边褶

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有很多小小的三角形骨突

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这些骨突会逐渐长大

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使头盾的边缘逐渐平滑

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这和厚头龙脑后的尖刺

301
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是类似的

302
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因为我的博物馆里有幼年的三角龙化石

303
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我就把它切开

304
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来看看

305
00:13:24,000 --> 00:13:27,000
结果发现小的三角龙骨头内部果然是海绵状的

306
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中等大小的骨头内部也是海绵状的

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但最有意思的是

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成年三角龙的骨头内部居然也是海绵状的

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它的头骨都达到两米长了

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非常的大

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不过在这个地层内出土的化石里面

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还有另一种恐龙

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与三角龙非常相似，只不过还要更大些

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叫做牛角龙

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当我们切开牛角龙骨头化石的时候

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发现骨质发育非常成熟

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但是牛角龙的头盾上有这种很大的孔洞

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所有人都说：

319
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三角龙和牛角龙不可能是同一种动物

320
00:14:03,000 --> 00:14:05,000
因为这种比那种大太多了

321
00:14:05,000 --> 00:14:10,000
（笑声）

322
00:14:10,000 --> 00:14:12,000
而且头上还有洞

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我就问他们：“你们见过小牛角龙吗？”

324
00:14:15,000 --> 00:14:18,000
他们回答：“这个还没有，

325
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但是它头上有洞啊”

326
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所以，我的学生约翰·斯堪那拉

327
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对我们所有馆藏的化石进行了研究

328
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他终于发现

329
00:14:28,000 --> 00:14:30,000
在三角龙身上

330
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这些洞就开始形成了

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00:14:32,000 --> 00:14:35,000
当然，到了牛角龙时期才完全打开

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约翰发现了一个处于

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00:14:38,000 --> 00:14:40,000
三角龙向牛角龙转型时期的化石

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非常的神奇

335
00:14:42,000 --> 00:14:44,000
所以，我们现在知道

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牛角龙其实是

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长大了的三角龙

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当我们给恐龙起名字

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或者说给任何东西起名字的时候

340
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都倾向于保留原有的那一个

341
00:14:55,000 --> 00:14:59,000
而放弃新取的那一个

342
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所以牛角龙就这么“灭绝”了

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至于三角龙，如果你看新闻的话

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就会发现好多新闻主播都搞错了

345
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他们认为应该保留“牛角龙”这个名字，而放弃“三角龙”

346
00:15:10,000 --> 00:15:12,000
但这是不会发生的

347
00:15:12,000 --> 00:15:17,000
（笑声）

348
00:15:18,000 --> 00:15:21,000
好，所以我们可以把这种方法用在许多种恐龙身上

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比如说，埃德蒙顿龙

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和大鸭龙

351
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顾名思义

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大鸭龙就是很大的鸭嘴恐龙

353
00:15:30,000 --> 00:15:32,000
它们也是一对这样的组合

354
00:15:32,000 --> 00:15:34,000
同样，我们还是从它们的骨组织入手

355
00:15:34,000 --> 00:15:37,000
骨质分析告诉我们

356
00:15:37,000 --> 00:15:39,000
埃德蒙顿龙是幼年恐龙

357
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或者顶多是青少年恐龙

358
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而大鸭龙则是成年恐龙

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根据个体发生学

360
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“大鸭龙”也灭绝了

361
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所以我们就可以一直不断地这么做

362
00:15:53,000 --> 00:15:55,000
最后我要讲的

363
00:15:55,000 --> 00:15:57,000
是雷克斯暴龙（即霸王龙）

364
00:15:57,000 --> 00:15:59,000
现在我们有两种恐龙

365
00:15:59,000 --> 00:16:02,000
暴龙和矮暴龙

366
00:16:02,000 --> 00:16:04,000
（笑声）

367
00:16:04,000 --> 00:16:07,000
现在我们自然而然产生怀疑了

368
00:16:07,000 --> 00:16:10,000
（笑声）

369
00:16:10,000 --> 00:16:12,000
但是他们的理由也很充分

370
00:16:12,000 --> 00:16:14,000
他们仔细检查后说：

371
00:16:14,000 --> 00:16:17,000
小的那个有17颗牙，大的才12颗牙

372
00:16:17,000 --> 00:16:19,000
这怎么可能是同一种呢？

373
00:16:19,000 --> 00:16:21,000
我们还不知道哪种恐龙

374
00:16:21,000 --> 00:16:23,000
是越长大牙越少的

375
00:16:23,000 --> 00:16:25,000
所以它们肯定

376
00:16:25,000 --> 00:16:28,000
是两种不同的恐龙

377
00:16:28,000 --> 00:16:30,000
所以我把它们都切开了

378
00:16:30,000 --> 00:16:32,000
果然和我想的一样

379
00:16:32,000 --> 00:16:35,000
矮暴龙是幼年的恐龙

380
00:16:35,000 --> 00:16:38,000
暴龙的骨头则成熟得多

381
00:16:38,000 --> 00:16:41,000
而且看起来还会继续长大

382
00:16:41,000 --> 00:16:43,000
在我工作的洛基博物馆里

383
00:16:43,000 --> 00:16:45,000
有四具暴龙化石

384
00:16:45,000 --> 00:16:47,000
所以我有机会把它们都切开来

385
00:16:47,000 --> 00:16:50,000
但是我发现我根本用不着这么做

386
00:16:50,000 --> 00:16:53,000
因为我只是简单地将它们的下颌骨按顺序排列起来

387
00:16:53,000 --> 00:16:56,000
就发现最大的一个有12颗牙

388
00:16:56,000 --> 00:16:58,000
第二大的有13颗牙

389
00:16:58,000 --> 00:17:00,000
第三大的有14颗牙

390
00:17:00,000 --> 00:17:02,000
当然了，矮暴龙有17颗牙

391
00:17:02,000 --> 00:17:05,000
然后我们就跑去其他博物馆里看别人收藏的暴龙

392
00:17:05,000 --> 00:17:09,000
发现了一只有15颗牙的

393
00:17:09,000 --> 00:17:12,000
这下事情又简单了

394
00:17:12,000 --> 00:17:14,000
暴龙（即霸王龙）的个体发生序列中

395
00:17:14,000 --> 00:17:17,000
是包括矮暴龙的

396
00:17:17,000 --> 00:17:22,000
这下我们又能从恐龙名单里划掉一个名字了

397
00:17:22,000 --> 00:17:24,000
（笑声）

398
00:17:24,000 --> 00:17:28,000
所以

399
00:17:28,000 --> 00:17:30,000
到了白垩纪末期

400
00:17:30,000 --> 00:17:33,000
我们还剩七种恐龙

401
00:17:33,000 --> 00:17:36,000
这个数字

402
00:17:36,000 --> 00:17:39,000
听起来就合理多了吧

403
00:17:39,000 --> 00:17:41,000
你也知道

404
00:17:41,000 --> 00:17:44,000
我这次演讲的主题对刚上四年级的小男生可能没什么吸引力

405
00:17:44,000 --> 00:17:46,000
他们喜欢他们的恐龙

406
00:17:46,000 --> 00:17:49,000
他们印象中的恐龙

407
00:17:51,000 --> 00:17:54,000
可不是这个样子的

408
00:17:54,000 --> 00:17:56,000
（笑声）

409
00:17:56,000 --> 00:17:58,000
谢谢大家！

410
00:17:58,000 --> 00:18:01,000
（鼓掌）