Jin Changzhu，of the Chinese Academy of Sciences(CAS)and lead author of the paper，said the smaller fossil skull indicates the giant pandas were about a third smaller than today’s pandas.

　　Researchers knew the panda reached its maximum size about 500,000 years ago，when it peaked，and then gradually became smaller.

　　Jin，a paleontologist(古生物学者)at the Institute of Vertebrate Paleontology and Paleoanthropology(古人类学)attached to the CAS，said the size variation was a basic rule of evolution.

　　“A species tends to grow bigger when it reaches the peak of its population，but becomes smaller when numbers decline，”he said.

　　The dental remains of the skull，which is the oldest giant panda skull ever found，are similar to today’s pandas’，indicating the type of teeth that could munch(用力嚼)mountains of bamboo.A panda can eat up to 40 kg of bamboo per day.

　　Paleoanthropologist Russell Ciochon，the US coauthor at the University of Iowa，said the panda’s focus on bamboo could have helped it survive all these years.

　　“Once an animal begins to rely on a common and stable food source，such as bamboo，it tends to evolve a larger body size，”he said.“As individuals of the evolving species grow bigger，they have a better chance not to be eaten by predators(肉食动物) due to their larger body size.”

　　【解题导语】　2001年在广西壮族自治区出土的一个大熊猫头骨化石证明，大熊猫在两百多万年前已经以竹子为主食，而且当时的大熊猫比如今的大熊猫小三分之一。本文介绍了这一考古发现的相关细节。

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