Oliver Milman “Flightless bird with giant head roamed swampy Arctic 53m years ago” https://www.theguardian.com/science/2016/feb/13/gastornis-flightless-bird-arctic-ellesmere-island
南極の飛べない鳥、つまりペンギンが氷山に阻まれて滅亡の危機に瀕している話に言及した*1。今度は北極の飛べない鳥の話。しかし、現代ではなく大昔。
現在のカナダ北極圏のエルズミーア島*2で、5300万年前の始新世*3にGastornis*4という高さ６フィート、体重数百ポンドの飛べない草食の鳥が生息していたことが確認された。Thomas Stidham氏（中国科学院）とJaelyn Eberleさん*5（コロラド大学）が、1970年代にエルズミーア島で発見された「爪先の骨の化石」を米国ワイオミング州で発掘されたGastornisの化石と比較した結果による*6。
世界で10番目に大きな島であるエルズミーア島は現在世界で最も寒い場所のひとつであるが、5300万年前は地球の気候が極度に温暖化した時代であり、エルズミーア島を含めて地球上に氷で覆われた土地は存在しなかった；
とはいえ、エルズミーア島のGastornisは冬になると南の方に移動していたようだ。それは冬になると、昼がなくなってしまうから。
Canada’s Ellesmere island is the 10th largest island in the world and lies adjacent to Greenland. Riven with fjords and attached to vast aprons of ice, Ellesmere is one of the coldest, driest and most remote places on Earth. Temperatures can reach -40C (-40F) in winter.It was a very different place 53m years ago, however, during the Eocene epoch. During this time, Antarctica was still attached to Australia and global temperatures were unusually warm, which meant the world was mostly ice-free. Ellesmere island would have been covered in the sort of cypress swamps now found much farther south in the US, with evidence that the area hosted turtles, alligators, primates and even large hippo-like and rhino-like mammals.
While apes and alligators won’t be returning to Ellesmere any time soon, the researchers said that the discovery of Gastornis provided a better understanding of the consequences of a changed climate.
“Permanent Arctic ice, which has been around for millennia, is on track to disappear,” Eberle said.
See also
“Giant flightless bird wandered the Arctic 50 million years ago” http://www.colorado.edu/news/releases/2016/02/12/giant-flightless-bird-wandered-arctic-50-million-years-ago
Christina Beck “This giant vegan bird prowled prehistoric Arctic” http://www.csmonitor.com/Science/2016/0212/This-giant-vegan-bird-prowled-prehistoric-Arctic
*1:“150,000 penguins die after giant iceberg renders colony landlocked” http://www.theguardian.com/world/2016/feb/13/150000-penguins-killed-after-giant-iceberg-renders-colony-landlocked Kim Arlington “Giant iceberg could wipe out Adélie penguin colony at Cape Denison, Antarctica” http://www.smh.com.au/environment/climate-change/giant-iceberg-could-wipe-out-adlie-penguin-colony-at-cape-denison-antarctica-20160212-gmslgx.html http://d.hatena.ne.jp/sumita-m/20160213/1455375035
*2:See eg. “Ellesmere Island” http://www.thecanadianencyclopedia.ca/en/article/ellesmere-island/ https://en.wikipedia.org/wiki/Ellesmere_Island https://ja.wikipedia.org/wiki/%E3%82%A8%E3%83%AB%E3%82%BA%E3%83%9F%E3%83%BC%E3%82%A2%E5%B3%B6
*3:See eg. “The Eocene Epoch” http://www.ucmp.berkeley.edu/tertiary/eocene.php https://en.wikipedia.org/wiki/Eocene https://ja.wikipedia.org/wiki/%E5%A7%8B%E6%96%B0%E4%B8%96
*4:See eg. https://en.wikipedia.org/wiki/Gastornis
*5:http://geode.colorado.edu/~eberlej/
*6:Thomas Stidham & Jaelyn Eberle “The palaeobiology of high latitude birds from the early Eocene greenhouse of Ellesmere Island, Arctic Canada” http://www.nature.com/articles/srep20912