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The researcher said they are also refuting the 'young canyon model', which claims the canyon was cut entirely in the last six million years. Instead, they show that the Colorado River used some old segments as it found its path from the Rockies to the Gulf of California in the past six million years.
These mammals lived in China about 130 million years ago.
The average extinction rate is now some 1,000 to 10,000 times faster than the rate that prevailed over the past sixty million years. Throughout most of geological history new species evolved faster than existing species disappeared, thus continuously increasing the planet's biological diversity.
They discovered the fossil in sediments, eroded rock particles in layers of earth strata, that belong to the Cretaceous Period (140-65 million years ago).
In rocks laid down as sediments as early as 18 million years ago, the researchers found the fossils of 20 species of rodents that haven't been reported anywhere else in South America.
Other evidence suggests grasses could have first appeared as far back as 80 million years ago.
(The Mesozoic era, which began about 225 million years ago and ended 65 million years ago, spans the period when dinos roamed Earth.) "Like modern kiwis, these flightless birds descended from a flying ancestor," Feduccia adds.
The earliest known tetrapods lived in regions that became Latvia and Scotland about 376 million years ago.
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.
Genetic detachment of human ancestors, or hominids, from chimps seems to have occurred on the X chromosome about 1.2 million years later than it did on other chromosomes, the scientists report.
Last year, for instance, researchers analyzed the lower jaw, skull fragments, and 40 percent of the skeleton of a chipmunk-size creature that lived 150 million years ago (SN: 4/30/05, p.
While most people are aware of the cataclysmic meteor impact that led to the extinction of the dinosaurs 65 million years ago, few know of the earlier, far greater, extinction of 95 percent of life on Earth.