人類「新品種」?坦尚尼亞發現366萬年前「交叉步」足跡

·2 分鐘 (閱讀時間)
A fossilized footprint dating from 3.66 million years ago from a site called Laetoli in northern Tanzania – attributed in a new study in the journal Nature to a species in the human evolutionary lineage – is seen in this handout photograph taken on June 21, 2019. Picture taken June 21, 2019.   Jeremy DeSilva/Handout via REUTERS NO RESALES. NO ARCHIVES. THIS IMAGE HAS BEEN SUPPLIED BY A THIRD PARTY.
考古學家在2019年6月紀錄萊托利腳印。圖片來源:REUTERS

考古學家近日證實,1976年在坦尚尼亞北部恩格羅恩格羅火山口(Ngorongoro Crater)西北部發現數個366萬年前的腳印化石,被稱為萊托利腳印(Laetoli footprints)。經徹底檢驗後,確認並非由原先認為的熊所製造,而可能是某種血統未知的「人類」,為人類進化史再添溯源資料,也代表人類直立行走的起源比已知的要複雜,研究發表於最新一期的《自然》(Nature)期刊。

International team of researchers work at a site called Laetoli in northern Tanzania, where a trackway of five fossilized footprints dating from 3.66 million years ago ? attributed in a new study in the journal Nature to a species in the human evolutionary lineage ? is seen in this handout photograph taken June in 2019. Shirley Rubin/Handout via REUTERS NO RESALES. NO ARCHIVES. THIS IMAGE HAS BEEN SUPPLIED BY A THIRD PARTY.
2019年6月考古學家們在萊托利遺跡研究。圖片來源:REUTERS

萊托利腳印目前有兩組,第2組在1978年被發現,與前一組相距1.6公里,被認為是阿法南方古猿種(Australopithecus afarensis)的古人類所留下;而此次又證實另一組也是人類腳印,即表明在數天、數小時或數分鐘內於同一層的火山灰形成的2組腳印,分屬兩種不同的人類。美國俄亥俄州大學古人類學家麥克紐特(Ellie McNutt)表示,萊托利腳印是人類化石紀錄中行走的最早證據。

A trackway of five fossilized footprints dating from 3.66 million years ago, attributed in a new study in the journal Nature to a species in the human evolutionary lineage, is seen in this handout photograph taken at a site called Laetoli in northern Tanzania  June 25, 2019 alongside a topographic depiction of the footprints highlighting their depth. Picture taken June 25, 2019. 
 Jeremy DeSilva, Catherine Miller and Austin Chad Hill/Handout via REUTERS
NO RESALES. NO ARCHIVES. THIS IMAGE HAS BEEN SUPPLIED BY A THIRD PARTY.
可清楚看見5個腳印並有前後交叉步的特徵。圖片來源:REUTERS

1976年的化石由5個連續足印組成,並且有(前後)「交叉步」(cross-stepping)的特徵,研究共同作者達特茅茲大學(Dartmouth College)古人類學家德席爾瓦(Jeremy DeSilva)說,「當我們在不平坦的道路上行走時,有時會出現交叉步,也許能解釋這種奇怪的步態;或者是一種未知的人類採用這種步態,我們還不能確定。」研究人員估計,足跡的主人身高可能略高於1公尺,走路時後腳跟明顯突出,大腳趾則往側面略微伸出。

大約6百到7百萬年前,人類與黑猩猩的系譜出現分歧,當人類祖先用雙腳行走時成為區別的關鍵點,但人類究竟何時開始行走,仍是未解之謎。萊托利遺址是一片廣闊的草原,對當時矮小的人類來說其實非常危險,與現代鬣狗、獅子及豹的祖先,還有已經滅絕的劍齒貓(aber-toothed cats)共同生活。

延伸閱讀》大發現!火山爆發近2千年 古羅馬城挖出人類遺骸