Incredible Fossilized Footprints of Giant Sloths詭異的大地懶腳印化石

勞拉·蓋格爾

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.

約1.1萬年前，一只形似大腳野人的地懶遇到了討厭的不速之客。一項新的研究表明，無論這只毛皮巨獸走到哪里，遠古人都會踩著它留下的扁長腎形爪印跟蹤而至。

終于，這只體型龐大的地懶似乎再也無法忍受了。根據對現場存留的腳印、爪印和爪痕化石的分析，這只巨獸用后腿直立起來——可能高達7英尺（2.1米）——向四周揮舞著的鋒利的鐮刀狀爪子，望著那些討厭的人類闖入者。

接下來發生了什么仍是未解之謎。馬修·貝內特說，遠古人可能試圖殺死這只地懶，而且很可能得逞了。貝內特是英國伯恩茅斯大學環境和地理科學教授、該研究項目合作者。

但是，研究人員在報告中寫道，鑒于現代狩獵者的大多數狩獵行動都不成功，加之“地懶肌肉如此發達”，用石器制服它會非常艱難，因此直接獵殺不太可能。

奇異腳印

2017年4月，研究人員在新墨西哥州白沙國家保護區發現了這種巨型地懶和遠古人留下的腳印。這項發現對該研究項目的首席研究員、國家公園管理局的戴維·布斯托斯來說是一個突破，他長期以來一直懷疑有遠古人的腳印化石隱藏在白沙保護區的土地上。

更令人驚訝的是，在地懶的足跡中發現了人類的一些腳印，這表明地懶剛剛走過不久，遠古人就踩著這些留在沙泥中的腳印追蹤而來。在這片化石豐富的地區，還發現了其他已滅絕的巨型動物的足跡，包括猛犸、郊狼、大型貓科動物、駱駝和牛等。

貝內特告訴科學鮮聞網：“在這個地區，各種動物和遠古人的足跡化石實際上有數十萬之多。”他補充說，這可能是美洲乃至全世界最大的足跡化石遺址。

然而，貝內特說，嵌有遠古人腳印的地懶腳印化石不足12個。研究人員說，這些地懶足跡可能是巨爪地懶或副磨齒獸留下的，也可能是幾只不同年齡段的地懶留下的。

呼喚福爾摩斯

這些腳印化石表明，在地球最后一次冰期結束時，遠古人和大地懶確實有過互動。這一證據是弄清遠古人是否跟蹤并獵捕這些毛皮巨獸的關鍵。與包括猛犸象和北美馬在內的其他大型哺乳動物一樣，大地懶也在這個時期前后滅絕了。

貝內特說，是人類捕獵者還是氣候變化最終導致了這些大型動物的滅絕，人們對此一直爭論不休。2016年發表在《科學》雜志上的一份研究報告表明，人類的種種破壞性活動和氣候變暖注定了冰期巨獸的滅絕。

除此之外，要像福爾摩斯那樣來破解1.1萬年前留下的足跡之謎，也是很難的。不過，研究人員提出了一些設想。一種設想是，遠古人在尾隨并侵擾這些大地懶，分散它們的注意力，這樣更容易獵殺它們。

另一種設想是，遠古人此舉是出于頑皮和好奇，并沒有惡意。研究人員在研究報告中寫道：“但人類與地懶的互動放在跟蹤和/或狩獵的背景下可能更好解釋。地懶是很難對付的獵物。它們強壯的手臂和鋒利的爪子賦予它們致命的攻擊力，在近距離遭遇戰中優勢明顯。”

威廉·哈考特-史密斯說，該研究很“可靠”——“他們對留下的足跡作了非常詳盡的記錄和分析”。哈考特-史密斯并未參與該項研究，他是雷曼學院和美國自然歷史博物館的古人類學家，這兩家機構都位于紐約市。

不過，哈考特-斯密斯表示，推想古代這一幕最好還是要慎重。很有可能是地懶留下爪印，而遠古人過了一個小時左右才跟上來——這意味著人類并未緊隨其后。

“兒童，甚至成人，有多少次只是為了好玩在雪地里或沙地上跟隨別人的腳步？”哈考特-史密斯對生命科學網說道。

然而，哈考特-史密斯說，地懶用巨大的爪子在地面上留下“甩動”痕跡很可能是人類的出現引起的。不過，他表示，沒有任何留存的武器或被殺動物的骨頭，誰都猜不出接下來到底發生了什么。

（譯者為“《英語世界》杯”翻譯大賽獲獎者）