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Rates of Dinosaur Body Mass Evolution Indicate 170 Million Years of Sustained Ecological Innovation on the Avian Stem Lineage.

Bird from extinction or due to "downsizing"
When almost all the dinosaurs are extinct 66 million years ago, and only those who have reduced - in other words, is the birds survived. Today, there are about more than 10,000 kinds of raw feathered birds flying in the sky, so that they become all fours animal species most abundant species. Recently, a new study reveals why this taxon has been so successful: This is because the rest of the birds before the dinosaurs disappeared long been "downsizing".
Was not involved in the study, University of Edinburgh paleontologist Stephen Brusatte said:. "This is a very impressive work, is the most comprehensive analysis conducted to date dinosaur body" Brusatte said: "This research Bird show is not all of a sudden becomes smaller, but the size is smaller end result of this long-term trend may be waiting thousands of years of time. "
When dinosaurs first appeared very small size. About 230 million years ago, dinosaurs most weight only 10-35 kg, size is only now a medium-sized dog so much. But many species quickly soared to tow a trailer-like size, in 30 million years to reach the 10,000 kg. Later, like a mighty dragon Argentina this dinosaur, whose head and tail length even with 35 meters, it weighs a staggering 90,000 kg.
Despite millions of years, there are many dinosaurs become bigger and more cumbersome, but there is a dinosaur seems to bet on the shape of narrow - hand dinosaur, which is a long feathered dinosaurs including the United States due to the movie "Jurassic Park" fame Raptor, which eventually created the appearance of birds.
To determine exactly how the dinosaur's body with the passage of time and change, by Oxford University paleontologist Roger Benson led a research team, the thickness of the hind leg bones of the dinosaur as an indicator of its overall weight, and thus the 426 kinds of dinosaurs The body size were assessed.
The researchers found that, in spite of all the dinosaurs are rapidly changing shape in the early stages of the evolution of dinosaurs - primarily grow bigger, but then this trend in almost all the dinosaurs are quickly slowed. In most cases, these dinosaurs subsequent urine remained at that level. However Maniraptora is an exception - this dinosaur continue to evolve into larger and smaller species, they expanded into a broader niche in the period of up to 170 million years time.
When an asteroid to hit Earth 66 million years ago, after, only those will be reduced to about 1 kg of body weight of raw feathered dinosaur hand, or the birds survived, perhaps due to their thin body to make it more easy to adapt to changes in the environment.
The researchers - on "Public Library of Science Biology 'reported their results of this study.
The researchers concluded that become smaller so Maniraptora easier to adapt to a wide variety of habitats, and those remaining dinosaurs - hinder their large size and the huge demand for food - but did not do it a little.
Not involved in the study of California Los Angeles County Museum of Natural History paleontologist Luis Chiappe believes that this body is reduced in terms of the evolution of flight is essential. He said, "flight For smaller animals would be easier" because "this would reduce the number of the need for energy." And Chiappe think, in this hand dinosaur millions of years more rapid change than any other body of dinosaurs, "they clearly are in different states of the birds tested."
Brusatte stressed: "The real story is not that interesting how some of the dinosaurs became so huge, but they are close relatives of birds and how to get it as small."
About the reasons for the extinction of dinosaurs it has been a controversy in scientific circles. Some scientists point out that in 66 million years ago, an asteroid hit the Earth in the Mexican coast, so there have been earthquakes and Earth firestorms caused by impact, while the hundreds of tons of material thrown into the atmosphere, blocking the sun's rays , so many biological loss of living space, including the dinosaurs. The study also pointed out that this impact but also for the evolution of many new species, including humans, provides an environment and conditions.