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Spirits of the ice forest -dinosaurs at the poles  

2010-08-11 03:53:18|  分类: 英文起步 |  标签: |举报 |字号 订阅

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http://www.bbc.co.uk/sn/prehistoric_life/dinosaurs/chronology/106mya1.shtml

Spirits of the ice forest -dinosaurs at the poles
image

Modern reptiles are cold blooded. However, a series of startling(惊人的) finds suggests there may have been dinosaurs living at the poles. What does this tell us about the possibility of warm-blooded dinosaurs. Dr Jo Wright investigates.

The idea that dinosaurs lived at the poles is based on remarkable finds made in Australia. There are two clues that Australia was once within the Antarctic Circle(南极圈). Firstly, we can can determine at what latitude rocks formed from the orientation of magnetic particles within them(可以通过岩石中磁性粒子的取向来判断岩石形成时所处纬度). Secondly, evidence that the climate was seasonally(季节性地) cold comes from both plant fossils and sedimentary structures(沉积构造) which form when the ground freezes.

A better picture

The fossil sites in Australia are remarkable because several different animals have been found, giving us a fuller picture of the palaeoenvironment(古环境) (life in the area at the time).

At least some of the animals must have been year-round(整年) residents – Leaellynasaura(雷利诺龙) were too small to have migrated(迁徙) hundreds of miles in and out every year. Leaellynasaura may have had a special adaptation for life in the polar regions.

Their skulls seem to have had especially large eye sockets(眼眶). Their large eyes may have allowed them to see better in the continuous low light levels of the polar winter.

Hanging in there

Some of the fossil vertebrates(脊椎动物) at these sites are very important because some very primitive animals that had become extinct elsewhere seem to have survived here. Labyrinthodont(迷齿亚纳动物) amphibians(两栖类), like Koolasuchus(酷拉龙), were previously thought to have died out over 100 million years earlier. In this environment it occupied a crocodilian niche(生态位,栖域), as the climate was too cold for crocodiles.

The earliest known dinosaur found in polar palaeolatitudes(古纬度) is called Cryolophosaurus(冰脊龙) (which means 'frozen crested reptile'), and was found in Antarctica. It is a meat-eating dinosaur but we do not know whether it migrated in during the summer months, or whether it lived there year round.

Dinosaurs from polar latitudes(纬度) have also been found in Alaska, but they are very similar to those from further south and are probably just a migrant population.


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Dwarf Allosaur(侏儒异龙) - Terror of the Antarctic - the largest killer there

The existence of dinosaurs at polar latitudes is significant. It means one of two things. Either dinosaurs had to hibernate(冬眠) or go into an inactive state in the polar winter. Or they had some way of maintaining a high body temperature - ie they were warm blooded.

Many people think that some, if not all(啊?), dinosaurs were warm blooded. These polar discoveries are strong evidence for warm-bloodedness in at least some dinosaurs.

This article was written to accompany episode five(第五集) of Walking with Dinosaurs.

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