For the whole of the Age of Dinosaurs, fewer than a thousand species have been identified (almost half of them known from a single specimen), 在整个恐龙时代，已经识别的还不足1000种（其中差不多半数是从一件标本得知的），

which is about a quarter of the number of mammal species alive now. 大约相当于现在活着的哺乳动物物种数的四分之一。

Dinosaurs, bear in mind, ruled the Earth for roughly three times as long as mammals have, 不要忘记，恐龙统治地球的时间差不多有3倍于哺乳动物统治地球的长度。

so either dinosaurs were remarkably unproductive of species or we have barely scratched the surface (to use an irresistibly apt cliche). 因此，要么恐龙的种类特别少，要么我们对恐龙才知道点儿皮毛（我禁不住使用这句合适的套话）。

For millions of years through the Age of Dinosaurs not a single fossil has yet been found. 恐龙时代有几百万年之长。但迄今为止一件恐龙化石也没有找到。

Even for the period of the late Cretaceous — the most studied prehistoric period there is, 即使在白垩纪末期——由于我们对恐龙和它们的灭绝怀有持久的兴趣，

thanks to our long interest in dinosaurs and their extinction — some three quarters of all species that lived may yet be undiscovered. 那是我们研究得最多的史前时期——在当时存在过的物种当中，大约四分之三也许还没有发现。

Animals bulkier than the Diplodocus or more forbidding than tyrannosaurus may have roamed the Earth in the thousands, and we may never know it. 几千头比梁龙更大或比霸王龙更威武的动物也许在地球上游荡过，而我们也许永远不会知道了。

Until very recently everything known about the dinosaurs of this period came from only about three hundred specimens representing just sixteen species. 直到最近，我们对这个时期的恐龙的全部认识，都出自仅有的大约300件标本，仅仅代表了16个物种。

The scantiness of the record led to the widespread belief that dinosaurs were on their way out already when the KT impact occurred. 由于缺少化石记录，许多人认为，恐龙在KT撞击发生的时候已经在走向没落。

In the late 1980s a paleontologist from the Milwaukee Public Museum, Peter Sheehan, decided to conduct an experiment. 20世纪80年代末，美国密尔沃基公共博物馆的古生物学家彼得·希恩决定搞一项试验。

Using two hundred volunteers, he made a painstaking census of a well-defined, but also well-picked-over, area of the famous Hell Creek formation in Montana. 他在蒙大拿州著名的赫尔克里克地层划出了一片区域，选用200名志愿者进行一次仔细的普查。