Every now and then,new clues surface, hinting at what else might lie beneath. ln this dried-up pond in South Dakota, known as Hot Springs, scientists unearthed great piles of bones. What kind of creature died here? The bones reveal it stood four metres tall and weighed more than 10 tonnes. There's nothing fitting that description living here today.
Here's the give-away, a pair of tusks two metres long, the trademark of a Columbian mammoth, the biggest animal to roam the ice age plains. By comparing it to elephants in Africa today, can we shed light on how those ice age elephants lived and what they lived on?
These are mammoth teeth, huge molars the size of bricks. They have deep ridges very similar to those of modern elephants, suggesting mammoths, too, survived by grinding vast amounts of grass.
Plant fragments trapped between the ridges can still be identified today. Thousands of years after this mammoth died, we know exactly what it ate for its last meal. Grass is a tough, abrasive food. Even with protective enamel ridges, these teeth would gradually have worn down. But just like modern elephants, the mammoths had evolved a way to deal with this. As one set of teeth was eroded8, another grew up to take its place. The evidence suggests they had six sets in all, to last a lifetime, up to 60 years.
The South Dakota mammoth didn't make it to old age and it was not alone. The site turned out to be a mammoth graveyard9, hiding more than 50 skeletons, all from animals in their prime. There's no sign they were killed by hunters, so how did so many healthy mammoths die?
1 unearthed
出土的(考古)
参考例句：
Many unearthed cultural relics are set forth in the exhibition hall. 展览馆里陈列着许多出土文物。
Some utensils were in a state of decay when they were unearthed. 有些器皿在出土时已经残破。
2 tusks
n.(象等动物的)长牙( tusk的名词复数 );獠牙;尖形物;尖头
参考例句：
The elephants are poached for their tusks. 为获取象牙而偷猎大象。
Elephant tusks, monkey tails and salt were used in some parts of Africa. 非洲的一些地区则使用象牙、猴尾和盐。 来自英语晨读30分(高一)
3 trademark
n.商标;特征;vt.注册的…商标
参考例句：
The trademark is registered on the book of the Patent Office.该商标已在专利局登记注册。
The trademark of the pen was changed.这钢笔的商标改了。
4 mammoth
n.长毛象;adj.长毛象似的，巨大的
参考例句：
You can only undertake mammoth changes if the finances are there.资金到位的情况下方可进行重大变革。
Building the new railroad will be a mammoth job.修建那条新铁路将是一项巨大工程。
5 ridges
n.脊( ridge的名词复数 );山脊;脊状突起;大气层的)高压脊
参考例句：
The path winds along mountain ridges. 峰回路转。
Perhaps that was the deepest truth in Ridges's nature. 在里奇斯的思想上，这大概可以算是天经地义第一条了。
6 abrasive
adj.使表面磨损的;粗糙的;恼人的
参考例句：
His abrasive manner has won him an unenviable notoriety.他生硬粗暴的态度让他声名狼藉。
She had abrasions to her wrists where the abrasive rope had scraped her.她的手腕有多出磨伤，那是被粗糙的绳子擦伤的。
7 enamel
n.珐琅，搪瓷，瓷釉;(牙齿的)珐琅质
参考例句：
I chipped the enamel on my front tooth when I fell over.我跌倒时门牙的珐琅质碰碎了。
He collected coloured enamel bowls from Yugoslavia.他藏有来自南斯拉夫的彩色搪瓷碗。
8 eroded
adj. 被侵蚀的，有蚀痕的 动词erode的过去式和过去分词形式
参考例句：
The cliff face has been steadily eroded by the sea. 峭壁表面逐渐被海水侵蚀。
The stream eroded a channel in the solid rock. 小溪在硬石中侵蚀成一条水道。
9 graveyard
n.坟场
参考例句：
All the town was drifting toward the graveyard.全镇的人都象流水似地向那坟场涌过去。
Living next to a graveyard would give me the creeps.居住在墓地旁边会使我毛骨悚然。
