Incredible Fossilized Footprints of Giant Sloths诡异的大地懒脚印化石

劳拉·盖格尔

A bigfoot-like ground sloth had unwelcome company about 11，000 years ago. No matter which way the giant creature went， ancient humans followed it， stepping in its elongated1， kidney-shaped paw prints as they tracked the furry beast， a new study suggests.

Finally， it seems that the giant ground sloth couldn’t take it anymore. It reared up on its hind legs—likely standing as tall as 7 feet （2.1 meters）—and swung its sharp， sickle-shaped claws around， looking at the unwanted human interlopers2， according to an analysis of the fossilized foot， paw and claw marks left at the site.

What happened next remains a mystery. It’s possible the humans attempted to kill the sloth and may have succeeded， said study co-researcher Matthew Bennett， a professor of environmental and geographical sciences at Bournemouth University in the United Kingdom.

But， given that the vast majority of hunts led by modern-day hunter-gatherers aren’t successful， and that “sloths are so densely muscled，” it would have been hard to overpower3 the animal with a stone weapon， so an outright4 kill is unlikely， the researchers wrote in the study.

Remarkable footprints

Researchers found the prints left by this giant ground sloth and humans in New Mexico’s White Sands National Monument park in April 2017. The find was a breakthrough for study lead researcher David Bustos， of the National Park Service， who had long suspected that fossilized footprints of ancient humans were hidden on the grounds of the monument.

Even more surprising was the fact that some of the human footprints were found inside the sloth tracks， indicating that ancient people had followed the prints while they were still fresh in the sandy mud. Track marks from other giant， now-extinct animals， including mammoths， wolves， big cats， camels and cattle have also been found on the fossil-rich site.

“There are literally hundreds of thousands of tracks of a variety of animals and humans [at the site]，” Bennett told Live Science. It’s likely the largest fossilized track mark site in the Americas， and possibly even the world， he added.

However， there were fewer than a dozen sloth track marks with human footprints inside， Bennett said. These sloth tracks were likely left by either Nothrotheriops or Paramylodon and were likely made by several animals of different ages， the researchers said.

Calling Sherlock Holmes

The prints reveal that ancient humans and giant ground sloths did， in fact， interact at the end of the last ice age. This evidence is key to figuring out whether humans stalked and hunted the furry giants， which went extinct around this time， as did other large mammals， including the mammoth and North American horse.

There’s an ongoing debate about whether human hunters or climate change ultimately led to the extinction of these large creatures， Bennett said. According to a 2016 study in the journal Science， a perfect storm5 of humans and a warming climate doomed the ice age giants.

Beyond this， it’s challenging to play Sherlock Holmes on a trackway that was made 11，000 years ago. But researchers have some ideas. One is that human hunters were following and harassing the giant ground sloths， distracting them so they could be more easily hunted， the researchers said.

Another idea is that humans’ actions were playful and curious rather than ominous6. “But human interactions with sloths are probably better interpreted in the context of stalking and/or hunting，” the researchers wrote in the study. “Sloths would have been formidable7 prey. Their strong arms and sharp claws gave them a lethal reach and clear advantage in close-quarter encounters.”

The study is a “solid” one—“they have done a very thorough job of documenting and analyzing the trackways，” said William Harcourt-Smith， a paleoanthropologist at Lehman College and the American Museum of Natural History， both based in New York City， who was not involved with the research.

But it’s good to be cautious when imagining the ancient scene， Harcourt-Smith said. It’s possible that the sloths made the tracks and humans followed an hour or so later—meaning that the humans weren’t hot on the sloths’ tail.

“How many times have children， or even adults， followed in the footsteps of others in the snow or sand， simply for the fun of it？” Harcourt-Smith told Live Science.

However， it’s definitely possible that the “flailing8” marks that the sloth made in the ground with its enormous claws were prompted9 by the presence of humans， Harcourt-Smith said. But without any surviving weapons or butchered animal bones， it’s anyone’s guess what happened next， he said.

约1.1万年前，一只形似大脚野人的地懒遇到了讨厌的不速之客。一项新的研究表明，无论这只毛皮巨兽走到哪里，远古人都会踩着它留下的扁长肾形爪印跟踪而至。

终于，这只体型庞大的地懒似乎再也无法忍受了。根据对现场存留的脚印、爪印和爪痕化石的分析，这只巨兽用后腿直立起来——可能高达7英尺（2.1米）——向四周挥舞着的锋利的镰刀状爪子，望着那些讨厌的人类闯入者。

接下来发生了什么仍是未解之谜。马修·贝内特说，远古人可能试图杀死这只地懒，而且很可能得逞了。贝内特是英国伯恩茅斯大学环境和地理科学教授、该研究项目合作者。

但是，研究人员在报告中写道，鉴于现代狩猎者的大多数狩猎行动都不成功，加之“地懒肌肉如此发达”，用石器制服它会非常艰难，因此直接猎杀不太可能。

奇异脚印

2017年4月，研究人员在新墨西哥州白沙国家保护区发现了这种巨型地懒和远古人留下的脚印。这项发现对该研究项目的首席研究员、国家公园管理局的戴维·布斯托斯来说是一个突破，他长期以来一直怀疑有远古人的脚印化石隐藏在白沙保护区的土地上。

更令人惊讶的是，在地懒的足迹中发现了人类的一些脚印，这表明地懒刚刚走过不久，远古人就踩着这些留在沙泥中的脚印追踪而来。在这片化石丰富的地区，还发现了其他已灭绝的巨型动物的足迹，包括猛犸、郊狼、大型猫科动物、骆驼和牛等。

贝内特告诉科学鲜闻网：“在这个地区，各种动物和远古人的足迹化石实际上有数十万之多。”他补充说，这可能是美洲乃至全世界最大的足迹化石遗址。

然而，贝内特说，嵌有远古人脚印的地懒脚印化石不足12个。研究人员说，这些地懒足迹可能是巨爪地懒或副磨齿兽留下的，也可能是几只不同年龄段的地懒留下的。

呼唤福尔摩斯

这些脚印化石表明，在地球最后一次冰期结束时，远古人和大地懒确实有过互动。这一证据是弄清远古人是否跟踪并猎捕这些毛皮巨兽的关键。与包括猛犸象和北美马在内的其他大型哺乳动物一样，大地懒也在这个时期前后灭绝了。

贝内特说，是人类捕猎者还是气候变化最终导致了这些大型动物的灭绝，人们对此一直争论不休。2016年发表在《科学》杂志上的一份研究报告表明，人类的种种破坏性活动和气候变暖注定了冰期巨兽的灭绝。

除此之外，要像福尔摩斯那样来破解1.1万年前留下的足迹之谜，也是很难的。不过，研究人员提出了一些设想。一种设想是，远古人在尾随并侵扰这些大地懒，分散它们的注意力，这样更容易猎杀它们。

另一种设想是，远古人此舉是出于顽皮和好奇，并没有恶意。研究人员在研究报告中写道：“但人类与地懒的互动放在跟踪和/或狩猎的背景下可能更好解释。地懒是很难对付的猎物。它们强壮的手臂和锋利的爪子赋予它们致命的攻击力，在近距离遭遇战中优势明显。”

威廉·哈考特-史密斯说，该研究很“可靠”——“他们对留下的足迹作了非常详尽的记录和分析”。哈考特-史密斯并未参与该项研究，他是雷曼学院和美国自然历史博物馆的古人类学家，这两家机构都位于纽约市。

不过，哈考特-斯密斯表示，推想古代这一幕最好还是要慎重。很有可能是地懒留下爪印，而远古人过了一个小时左右才跟上来——这意味着人类并未紧随其后。

“儿童，甚至成人，有多少次只是为了好玩在雪地里或沙地上跟随别人的脚步？”哈考特-史密斯对生命科学网说道。

然而，哈考特-史密斯说，地懒用巨大的爪子在地面上留下“甩动”痕迹很可能是人类的出现引起的。不过，他表示，没有任何留存的武器或被杀动物的骨头，谁都猜不出接下来到底发生了什么。

（译者为“《英语世界》杯”翻译大赛获奖者）