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6 LEPTICTIDIUM (Delicate Weasel): Lived 50-40 million years ago.
It lived about 164 million years ago in northeastern China.
Although the planet's earliest plants were algae, which appeared only in oceans more than 1 billion years ago, by 500 million years ago some plants had adapted to survival outside water.
Since the cold engulfed Antarctica at the beginning of the last ice age, 30 million years ago, it has been virtually untouched by most forms of life.
Archaeopteryx, the earliest known bird, dates back to 150 million years ago.
Just before the dinosaurs died out about 65 million years ago, mammals called gondwanatheres appeared on Earth.
At the same time the Gobi group was digging up Mononychus bones, another group of scientists was disovering some interesting things about the most primitive flying bird, Archaeopteryx, which lived 147 million years ago.
The findings suggest that archaeopteryx, a reptilian bird that lived 145 million to 150 million years ago, and its close kin were not direct links between reptiles and today's birds, but evolutionary dead ends.
The discovery of previously unknown rodent species that lived in Chile millions of years ago suggests that mountains in the southern Andes first rose to significant heights at least 18 million years ago.
The North American continent and many of its creatures were fried 65 million years ago in a nightmarish ``corridor of incineration'' - an immense, white-hot jet that gushed from an asteroid crash in Mexico, scientists say.
The skull structure of Acanthostega, a semiaquatic creature that lived about 365 million years ago, suggests that although the creature spent most of its time in the water, it fed on shore or in the shallows rather than in deep water.
Twenty-five million years ago, the area that is now a deep rut in the ground was a granite plain, Reynolds said.