Stidham Thomas A, Eberle Jaelyn J
Key Laboratory of Vertebrate Evolution and Human Origins, Institute of Vertebrate Paleontology and Paleoanthropology, Chinese Academy of Sciences, Beijing 100044, China.
University of Colorado Museum of Natural History and Department of Geological Sciences, University of Colorado at Boulder, 265 UCB, Boulder, CO 80309, USA.
Sci Rep. 2016 Feb 12;6:20912. doi: 10.1038/srep20912.
Fossils attributable to the extinct waterfowl clade Presbyornithidae and the large flightless Gastornithidae from the early Eocene (~52-53 Ma) of Ellesmere Island, in northernmost Canada are the oldest Cenozoic avian fossils from the Arctic. Except for its slightly larger size, the Arctic presbyornithid humerus is not distinguishable from fossils of Presbyornis pervetus from the western United States, and the Gastornis phalanx is within the known size range of mid-latitude individuals. The occurrence of Presbyornis above the Arctic Circle in the Eocene could be the result of annual migration like that of its living duck and geese relatives, or it may have been a year-round resident similar to some Eocene mammals on Ellesmere and some extant species of sea ducks. Gastornis, along with some of the mammalian and reptilian members of the Eocene Arctic fauna, likely over-wintered in the Arctic. Despite the milder (above freezing) Eocene climate on Ellesmere Island, prolonged periods of darkness occurred during the winter. Presence of these extinct birds at both mid and high latitudes on the northern continents provides evidence that future increases in climatic warming (closer to Eocene levels) could lead to the establishment of new migratory or resident populations within the Arctic Circle.
来自加拿大最北部埃尔斯米尔岛始新世早期（约5200 - 5300万年前）的、可归因于已灭绝水鸟分支Presbyornithidae和大型不会飞的Gastornithidae的化石，是北极地区最古老的新生代鸟类化石。除了尺寸稍大一些外，北极Presbyornithidae的肱骨与美国西部的Pervetus Presbyornis化石没有区别，而Gastornis的趾骨在中纬度个体已知的尺寸范围内。始新世时Presbyornis出现在北极圈以北，可能是像其现存的鸭和鹅亲属那样进行年度迁徙的结果，或者它可能是常年居住者，类似于埃尔斯米尔岛上的一些始新世哺乳动物和一些现存的海鸭物种。Gastornis与始新世北极动物群的一些哺乳动物和爬行动物成员一样，可能在北极过冬。尽管埃尔斯米尔岛始新世气候较为温和（高于冰点），但冬季仍会出现长时间的黑暗。这些已灭绝鸟类在北半球中高纬度地区的存在表明，未来气候变暖加剧（接近始新世水平）可能导致北极圈内出现新的迁徙或常驻种群。
