经济学人下载:谁吃了恐龙 What Ate Dinosaurs?

What ate dinosaurs?
谁吃了恐龙

Old crocs
古鳄鱼

Even in their heyday, dinosaurs were not quite as dominant as popular myth makes them out to be
即便是在全盛时期，恐龙并非像民间传说所理解的那样占绝对统治地位

ONE answer to the question, “What ate dinosaurs?” is, obviously, “Other dinosaurs.” The ropod predators like Tyrannosaurus and Allosaurus loom large in the imagination of every lover of prehistoric monsters, and their animatronic fights with the likes of Diplodocus and Stegosaurus are the stuff of cliché. Science, though, tries to look beyond the obvious, and at this year’s meeting of the Society of Vertebrate Palaeontology, held in Las Vegas, some of the speakers asked whether the top predators of the Mesozoic era really were all dinosaurs. Their conclusion was “no”. Another group of reptiles, until recently neglected, were also important carnivores. And it is a group that is still around today: the crocodiles.
“谁吃恐龙”很明显，其中一个答案是：“其它恐龙”每个史前怪兽爱好者的脑海里浮现出的是像霸王龙、翼龙这样的兽脚类掠食者，电脑制作的它们与梁龙、剑龙的打斗也成为俗套。而科学试图不落窠臼。今年，在拉斯维加斯召开的古脊椎生物学会会议上，一些发言人问到中生代顶级掠食者是否全是恐龙，结论是“否”。直到最近还被忽视的一类爬虫，同样是重要的食肉动物，正是仍然存活于今的一个族群：鳄鱼。

That the past role of crocodiles (or, strictly, crocodilians, since they came in many sizes and shapes, not all of which resemble the modern animals) has been underestimated was suggested a few years ago by Paul Sereno. Dr Sereno, a palaeontologist at the University of Chicago, uncovered a crocodile-dominated ecosystem from about 100m years ago (the middle of the Cretaceous period), in what is now north Africa. Besides water-dwelling giants similar to (though much bigger than) today’s animals, he found a range of forms including vegetarians and species that ran on elongated legs—more like dogs than crocodiles. That discovery has prompted other fossil hunters to look elsewhere. As a result, even the well-studied rocks of North America are revealing that dinosaurs did not have it all their own way in the ecosystems of the Mesozoic—as Stephanie Drumheller of the University of Iowa and Clint Boyd of the University of Texas at Austin explained to the meeting.
几年前，芝加哥大学古生物学家保罗•赛伦诺博士提出鳄鱼过去的角色（或者从严格意义上讲是鳄鱼目动物，因为它们形状大小各异，并非所有都类似现代鳄鱼）被低估了，在今天的北非，他发现了一个一亿年前（白垩纪中期）由鳄鱼占主导地位的生态系统。除了与现代鳄鱼同为水生巨兽外（但远比现代的大），他还发现了一系列包括食草的、用长腿行走的——比起鳄鱼来更像狗的种群及形态。这一发现促使其他化石探寻者着眼于其它地方。结果是，即便是那些出自北美的已经研究得很透彻的化石也显示出恐龙并非占据中生代生态系统全部位置。——正如衣阿华大学的斯蒂芬妮•庄姆海勒以及位于奥斯汀的德克萨斯大学的克林特•博依德在会上说的那样。

The Cretaceous equivalent of zebra and antelopes—the victim species in every wildlife documentary about the dramas of the African savannah—were herbivorous dinosaurs called ornithopods. Frequently, these were taken by theropods. But not always. When Ms Drumheller and Mr Boyd examined the bones of juvenile upper-Cretaceous ornithopods dug up in Utah they saw marks on one skeleton that looked suspiciously like those modern crocodiles inflict when biting and tearing at their prey. On examining these marks more closely, they found a crocodilian tooth stuck in one of them.
白垩纪被称为鸟脚亚目食草恐龙其地位相当于斑马和羚羊——每部有关非洲大草原的纪录片中被捕杀的种群。这些恐龙经常被兽脚亚目食肉恐龙捕食。但不总是这样，当庄姆海勒与博依德对犹他州出土的白垩纪年幼的鸟脚亚目食草恐龙的化石进行检查时，他们在一副骨架上发现了看上去像是遭受现代鳄鱼撕咬的痕迹。在对这些痕迹进一步检查后，他们发现一颗鳄鱼目动物牙齿嵌在其中一块骨头上。

Crocodile tears
鳄鱼的眼泪

It was not a large tooth. Its size suggests the animal which made it was no more than a metre and a half (about 5 feet) long. Such a predator would have been unable to take on an adult ornithopod. Nevertheless, this tooth is the first unarguable proof that crocodilians did indeed snack on dinosaurs. Moreover, it helps to confirm suspicions that the other crocodile-bite-like marks that Ms Drumheller and Mr Boyd have discovered really are what they look like. By combining that with an analysis of the whole site, the two researchers argue that what they have discovered is a dinosaur nesting ground that was being raided by crocodilians.
这颗牙不是很大，其尺寸表明牙齿的主人不超过一米五（约五英尺）这样的掠食者本不能捕食一头成年鸟脚亚目食草恐龙。但无可争辩的是，这颗牙是第一个鳄鱼目动物拿恐龙当点心的证据。此外，这也有助于消除对庄姆海勒与博依德发现的其它看似鳄鱼咬痕的怀疑。结合对这个地区的分析，两位研究者认为他们所发现的是一个遭到鳄鱼目动物偷袭的恐龙筑巢地。

Such suspicions have been aroused before. Other sites in Utah are known to be dinosaur nesting grounds, since eggs are found there. Crocodilian bones frequently turn up at such sites. Ms Drumheller and Mr Boyd, however, seem to have nailed the connection down. Juvenile dinosaurs, at least, were indeed the prey of crocodilians. But what about adults?
这样的怀疑以前也出现过。由于发现了恐龙蛋，人们知道犹他州还有其它恐龙筑巢地。在这些地区，鳄鱼目动物化石经常被发现。可庄姆海勒与博依德像是要明确这一关系，年幼恐龙至少是鳄鱼目动物的猎物，那么成年的呢？

More than mere morsels
不仅仅是少数

To investigate that question, Martin Lockley at the University of Colorado, Denver, and Spencer Lucas of the New Mexico Museum of Natural History and Science, turned to one of the most famous fossil phenomena on the planet—the dinosaur freeway that runs through Colorado, New Mexico, Kansas and Oklahoma. This collection of tracks, scattered over several sites of the same age along the coast of an inland sea, is thought to mark an ancient migration route. The traces of more than 1,380 individual animals can be distinguished. Most, but not all, were ornithopods. Some were small carnivorous dinosaurs—the sort that might pick off young stragglers in the way that the crocodilians identified by Ms Drumheller and Mr Boyd did. But there is, Dr Lockley and Dr Lucas realised, something missing from the picture. When they looked for traces of big predatory dinosaurs, they found none.
为了弄清这一问题，丹佛科罗拉多大学的马丁•洛克里以及新墨西哥州自然历史博物馆的斯派瑟•卢卡斯将目光转向世上最著名的化石现象之一——横穿科罗拉多、新墨西哥、堪萨斯、俄荷拉荷玛的恐龙公路。于同一年代沿着一个内陆海海岸分布在数个地区，这一汇集恐龙踪迹的地区被认为是标出了一条古老的迁徙路线。人们能区分出超过1380种不同动物的踪迹。绝大部分是鸟脚亚目食草恐龙。一些是小型食肉恐龙——正如庄姆海勒与博依德所确认的鳄鱼目动物那样，这些恐龙会截杀年幼离群的食草恐龙。但洛克里与卢卡斯博士明白，图上遗漏了一些东西。当他们寻找大型掠食恐龙的线索时，他们什么也没发现。

That is ecologically absurd. Unless, of course, the top predator of the system—the one that could hunt down adult ornithopods—was not a dinosaur at all. And, when Dr Lockley and Dr Lucas re-examined the tracks they found that that was exactly what was going on. Instead of theropod footmarks, they found those of crocodilians. More than a quarter of the places where the dinosaur freeway surfaces have yielded signs of crocs. And they were big: sometimes more than four metres long. That is certainly large enough to take on an adult ornithopod.
从生物学上讲，这是荒唐的。当然除非生态系统的顶级掠食者——即是能捕杀成年的鸟脚亚目食草恐龙的——并不完全是恐龙。而且，当洛克里与卢卡斯博士对这些线索进行重新检查时，他们发现那正是曾经所发生的。在出土的恐龙公路上，超过1/4的地区已发现鳄鱼的踪迹。而且它们很大：有时超过4米长，大到足以捕杀一头成年鸟脚亚目食草恐龙。

Such megacrocs, then, could easily have acted as top predators in this ecosystem. But that does not completely explain the absence of theropod tracks. Modern migrating herbivores fall victim to many sorts of carnivore: big cats, wolves and hyenas, to name but three. The marshy conditions of the dinosaur freeway (the reason its footprints formed, and have survived) may, though, have favoured crocodilians over predators that had evolved on drier land. In that sort of environment even a big theropod would constantly have been looking over its shoulder. Perhaps the real reason why they did not plant their footprints on the dinosaur freeway is that they might have ended up as prey, as well.
这样的巨鳄能在这样的生态系统中轻松担当顶级掠食者的角色。但这并不能完全解释兽脚亚目食肉恐龙的缺位。现代迁徙类食草动物成为众多食肉动物的牺牲品：大型猫科动物、狼、鬣狗，就拿这三样来说。然而，比起在干燥陆地上进化的掠食者，恐龙公路所处的湿地环境（形成并使恐龙足迹得以保存的原因）也许更受鳄鱼目动物欢迎。在那样一种环境下，即便是一头巨大的兽脚亚目食肉恐龙也会不时回头张望。它们为何没有在恐龙公路上留下足迹呢？真正的原因或许是它们同样亡于其它掠食者。