英语听力：冰河绿洲—10

This is the Virginia opossum, a tree dweller found throughout many of the southern states. It's the only North American marsupial. The young are born premature and matured in the mother's pouch. And its only close relatives today are found in Central and South America. The opossum is a rare survivor from a South America invasion.

In the ice age, there were many other species that had travelled north to Florida, including a giant. This spectacular claw is 40cm long. And it belonged to a creature whose fossil remains have been found throughout Florida. It's the claw from a giant ground sloth and it really was a giant—6 metres long and weighing up to 40 tons. It rivalled the mammoth in size.

Although the giant ground sloth is now extinct, like the opossum, it has family ties in South America. The family resemblance is easy to see. These menacing claws are used as grappling hooks, not weapons. They belong to the tree sloth, a peaceful vegetarian that spends its time eating leaves. It seems a far cry from our vision and an ice age beast.