Sun, Jun 17, 2018 - Page 9 News List

South African fossils rewrite early history of life on land
南非發現化石 重寫早期陸上生命史

Two newly discovered early amphibians Tutusius and Umzantsia that lived about 360 million years ago during the Devonian Period are shown in this artistic illustration, released June 7.
這張六月七日發布的模擬圖,展示兩種新發現的早期兩棲類動物Tutusius與Umzantsia,這兩種動物大約生活在三億六千萬年前的泥盆紀。

Photo: Reuters
照片:路透

Fossils of two amphibians that lived within the Antarctic circle 360 million years ago are forcing scientists to rethink the origins of land vertebrates, including where these pioneers first appeared and the climatic conditions that spawned them.

Scientists said on June 7 they have unearthed partial remains of primitive Devonian Period amphibians named Tutusius umlambo and Umzantsia amazana at a site called Waterloo Farm near Grahamstown, South Africa. While the fossils are fragmentary, the researchers said Tutusius and Umzantsia most likely shared the four-legged, alligator-crossed-with-a-fish body plan of the earliest amphibians, eating small fish while in the water and perhaps small invertebrates while on land.

Umzantsia was about 28cm long with a long, slender lower jaw, apparently armed with small pointed teeth. Tutusius, known from a single shoulder girdle bone, was about 1m long. It was named in honor of South African Anglican cleric and human rights activist Desmond Tutu. They were among the early wave of tetrapods, a group including all land-living vertebrates. The first tetrapods evolved from fish during the Devonian. Until now, it had been thought that this evolution revolution occurred in warm climes because the fossils of all the earliest-known amphibians, as well as their fish forerunners, had been found in places that were tropical or subtropical at the time.

Africa during the Devonian was part of a super-continent called Gondwana that also encompassed South America, India, Australia and Antarctica. The Waterloo Farm site was within the Arctic circle. “So we now know that tetrapods, by the end of the Devonian, lived all over the world, from the tropics to the Antarctic circle,” said paleontologist Robert Gess, based at the Albany Museum in Grahamstown as part of the South African Centre of Excellence in Palaeosciences, at the University of the Witwatersrand. “So it’s possible that they originated anywhere and that they could have moved onto land anywhere. It really broadens the scope of possibilities,” Gess added.

The Waterloo Farm site was a river-mouth environment, a tidal estuary opening onto the sea, and likely had a cold climate akin to northern Norway’s Atlantic coast, said paleontologist Per Ahlberg of the University of Uppsala in Sweden. “There would certainly have been several months of winter darkness, as well as midnight sun in the summer,” Ahlberg said, adding that it probably snowed in wintertime.

The research was published in the journal Science.

(Reuters)

三億六千萬年前生活在南極圈內兩種兩棲類動物的化石,迫使科學家重新思考陸生脊椎動物的起源,包括這些開路先鋒最初在哪裡出現,以及什麼樣的氣候條件讓它們得以繁衍。

科學家六月七日表示,他們在南非格拉罕鎮附近的沃特盧農場,挖掘到泥盆紀原始兩棲類動物Tutusius umlambo與Umzantsia amazana的部分遺骸。雖然化石破碎不全,研究人員指出Tutusius與Umzantsia很有可能和最早的兩棲類動物一樣,具有四條腿以及混合短吻鱷和魚類的身型,在水中攝食小魚,也可能會在陸地上捕食小型無脊椎動物。

Umzantsia身長約二十八公分,下顎長而纖細,明顯配有小而尖銳的牙齒。Tutusius的發現來自於一根肩帶骨,身長大概一公尺,其命名是為了紀念南非聖公會宗教領袖暨人權運動家戴斯蒙‧屠圖。這兩個物種屬於四足動物──這類涵蓋所有陸生脊椎動物的族群──早期演化浪潮中的一部分。最初的四足動物在泥盆紀時期從魚類演化而來。到目前為止,這場演化革命一直被認為在溫暖的氣候帶發生,因為目前所知最早的兩棲類動物和它們的魚類祖先化石,全都發現於當時曾屬於熱帶或亞熱帶的地區。

泥盆紀時期的非洲屬於超級大陸岡瓦那的一部分,岡瓦那大陸也涵蓋南美洲、印度、澳洲,和南極洲。沃特盧農場當時仍然在南極圈內。「所以我們現在知道,到了泥盆紀末期,四足動物已經廣泛生活在世界各地,從熱帶到南極圈都有他們的蹤影,」奧爾巴尼博物館的駐館古生物學家羅伯特‧吉斯說。該博物館位於格拉罕鎮,屬於金山大學南非古科學研究中心的一部分。吉斯補充表示:「所以這些四足動物可能起源於任何一個地方,而且可能在地球上任何一處登陸。這確實大為擴展了可能性的範圍。」

瑞典烏普薩拉大學的古生物學家佩‧阿柏格表示,沃特盧農場的位址曾屬於河口環境,是一個開口向海,會受潮汐影響的河口灣,當時氣候條件可能類似挪威北方的大西洋沿岸。阿柏格指出:「那時冬天一定有好幾個月不見天日,夏天也會有永晝的現象」,並補充表示該地區以前冬天可能也會降雪。

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