The dinosaurs¹ were already in decline 50 million years before the asteroid² strike that finally wiped them out, a new study suggests.

近日，一项最新研究显示，在小行星撞击地球、最终导致恐龙灭绝的五千万年前，恐龙数量已经在逐步减少。

The new assessment³ adds further fuel to a debate on how dinosaurs were doing when a 10km-wide space rock slammed into Earth 66 million years ago.

在人们争论恐龙究竟在6600万年前那个10km宽的太空陨石撞击地球时做什么的时候，这项新的评估无疑为这场争论火上浇油。

A team suggests the creatures were in long-term decline because they could not cope with the ways Earth was changing. The study appears in PNAS journal.

一个研究小组表示，由于不能适应地球的变化，恐龙在很长一段时间内数量有所下降。这项研究刊登在美国科学院院刊。

Researchers analysed the fossil remains⁴ of dinosaurs from the point they emerged 231 million years ago up to the point they went extinct. To begin with, new species evolved at an explosive rate. But things started to slow about 160 million years ago, leading to a decline in the number of species which commences at about 120 million years ago.

研究者对恐龙于2.31亿年前出现直至灭绝期间的恐龙化石进行了分析。最开始，新物种以爆炸性的速度出现，但1.6亿年前这个过程开始放缓，导致在1.2亿年前恐龙数量开始减少。

Dr Manabu Sakamoto, a palaeontologist from the University of Reading, who led the research, said: "We were not expecting this result. Even though they were wiped out ultimately by the impact of the asteroid, they were actually already on their way out around 50 million years before the asteroid hit."

英国雷丁大学古生物学家Manabu Sakamoto博士主导这项研究，他说：“我们没料到是这样的结果。尽管恐龙是由于小行星撞地球而灭绝，但在这之前，即距今约5000万年前，恐龙已经开始走向衰落。”

Dr Sakamoto's analysis shows that the long-necked giant sauropod dinosaurs were declining the fastest, whereas theropods, the group of dinosaurs that included the iconic Tyrannosaurus rex, were in a more gradual decline.

Skamoto博士的分析表明，长颈巨型蜥脚类恐龙衰亡速度最快，而以雷克斯霸王龙为代表的兽角类恐龙数量下降则较为缓慢。

Co-author Dr Chris Venditti, an evolutionary⁵ biologist from the University of Reading, told BBC News:

来自雷丁大学的演化生物学家、论文联合作者Chris Venditti博士告诉BBC：

"The current widespread view is that dinosaurs were reigning⁶ strong right up to the impact that hit the Earth - and it's the impact that drove their final extinction," he said. "And while that's certainly true, what we found was that they were on the decline long before that."

“目前普遍认为恐龙在小行星撞地球前统治着地球。而小行星撞击也是导致它们最终灭绝的原因。”他说。“这当然是事实，但我们发现它们早在那之前就已经走向衰亡。”

Dr Venditti believes that the dinosaurs' 50 million year decline rendered them even more susceptible⁷ to the environmental catastrophe⁸ that followed the asteroid impact. "If they were reigning strong perhaps they would have fared much better than they did," he said.

Venditti博士认为，恐龙在5000万年前数量的减少导致它们更易受到小行星撞地球过后的环境大灾难影响。他说：“如果它们数量再多些，可能会更好地适应这种情况。”

The asteroid impact is commonly thought to have paved the way for mammals to take over. But the new study suggests that mammalian supremacy⁹ might have occurred eventually, without a space impact.

人们普遍认为，小行星撞地球为哺乳动物的翻身铺平了道路。但新的研究表明，即使小行星没有撞击地球，哺乳动物最终也会统治地球。

Co-author Prof Mike Benton of Bristol University, told BBC News: "World climates were getting cooler all the time. Dinosaurs rely on quite warm climates and mammals are better adapted to the cold. So there might have been a switch over in any case without the asteroid impact."

论文的联合作者、布里斯托大学德Mike Benton教授告诉BBC：“全球气候一直在变冷，恐龙适合在温暖的气候条件下生存，而哺乳动物更好地适应了寒冷的气候。因此，无论是否有小行星撞地球，最终哺乳动物都会取代恐龙。”