３６００万年前のクジラ化石、ペルーの砂漠で発見

【ＡＦＰ＝時事】３６００万年前の海に生息していた古代のクジラの化石が今月、南米ペルーの首都リマの博物館で公開された。（写真はペルーのオクカヘ砂漠で発見された初期クジラ類「バシロサウルス」の頭骨化石。同国首都リマの博物館で公開）
　ペルー国立サンマルコス大学などの研究チームによると、この初期クジラ類「バシロサウルス」の新たな化石は昨年末、リマ南方約３５０キロのイカ州にあるオクカヘ砂漠で発見された頭骨で、完全な形で残っていた。荒涼としたこの一帯は数千万年前、浅い海だった。
　研究者の間でこのバシロサウルスは「オクカヘのプレデター（捕食者）」と呼ばれている。全長約１７メートルで、非常に大きく強力な歯で獲物を捕らえていた。
　チームを率いる古生物学者のマリオ・ウルビナ氏は「同様の標本は世界で他に見つかっていないため、今回の発見は非常に重要だ」と話す。
　研究者の一人によると、このバシロサウルスは既知の他の古代クジラ類と比較して、体の大きさと歯の発達という２点が際立っている。この２点はどちらも食物連鎖の頂点に立っていた可能性が高いことを示している。「当時最大級の肉食動物だった」という。
　バシロサウルスのような初期のクジラ類は、約５５００万年前に陸生動物から進化し、始新世（約５６００万年前～３４００万年前）後期には海洋生活に完全に適応していた。
　研究チームによれば現生クジラ類は当時まだ進化しておらず、クジラ類はほぼ全てが比較的巨大な海洋捕食動物だった。【翻訳編集ＡＦＰＢＢＮｅｗｓ】
〔ＡＦＰ＝時事〕（2022/03/31-09:21）

Paleontologists on Thursday unveiled the fossilized remains of an ancient whale that inhabited the seas 36 million years ago, found last year in a Peruvian desert.
We have presented the new Peruvian basilosaurus, it is the complete skull of an archaic whale that lived 36 million years ago, paleontologist Mario Urbina, head of the team that discovered the skeleton, told AFP.
Urbina said the basilosaurus was found at the end of 2021 in the Ocucaje Desert in the Ica department, about 350 kilometers (215 miles) south of Lima. The desolate landscape was a shallow sea millions of years ago, and its dunes have yielded large numbers of striking primitive sea mammal remains.
The Ocucaje Predator, as the researchers dubbed it, was about 17 meters (55 feet) long and used its massive, powerful teeth to feed on tuna, sharks and schools of sardines.
This finding is very important because there are no other similar specimens discovered in the world, said Urbina, a researcher at the National University of San Marcos, in Lima.
Team member Rodolfo Salas-Gismondi explained the basilosaurus differs from other known ancient whale species by its size and the development of its teeth, both of which indicate the animal was likely at the top of the food chain.
This is an extraordinary find because of its great state of preservation, he told AFP. This animal was one of the largest predators of its time.
At that time the Peruvian sea was warm, added Salas-Gismondi, who heads the Department of Vertebrate Paleontology at the Natural History Museum in Lima. Thanks to this type of fossil, we can reconstruct the history of the Peruvian sea.
The first cetaceans, like the basilosaurus, evolved from land animals some 55 million years ago.
By the late Eocene period (between 56 million and 34 million years ago), cetaceans had fully adapted to marine life.
Whales had not yet evolved, and almost all cetaceans were marine macropredators, according to the research team.
The Ocucaje Desert is rich in fossils, the researchers said, providing scientists with 42 million years' worth of evolutionary evidence.
Other fossils found there include four-legged dwarf whales, dolphins, sharks and other species from the Miocene period (between 23 million and five million years ago).