Washington, Oct 24: A team of scientists led by University of Washington paleontologist Peter Ward has concluded that a fluctuations in oxygen levels in the Earth's atmosphere was responsible for the survival of only dinosaurs and the extinction of other anthropods.
According to Ward and his research team, dinosaurs first appeared in the last part of the Triassic Period, about 230 million years ago, when atmospheric oxygen content was at its lowest. Ward, however, speculates that when oxygen levels rose again, it contributed to the eventual gargantuan growth of dinosaurs, as we now know them.
"Dinosaurs thrived and nothing else did. There's an explanation for that, and it is that the air sac breathing system in dinosaurs and their descendants, modern birds, is more efficient than systems used by other organisms," Ward claims.
He contends that atmospheric oxygen rose sharply at the end of the Silurian Period, about 415 million years ago, to reach a level of about 22 percent of the atmosphere, similar to today's oxygen content. But 55 million years later, atmospheric oxygen levels sank to between 10 and 13 percent, and remained at that level for 30 million years
This period and the resultant mysterious lull in vertebrate colonization of land is known as Romer's Gap, named for the Yale University paleontologist, Alfred Romer, who first recognized this link between oxygen levels and animal life on Earth all those millions of years ago.
The term, however, has only been applied to pre-dinosaur amphibians, and there has been little understanding of why the gap occurred.
According to Ward, there were two waves of vertebrate colonization of the land.
"In the first wave, the animals' lungs couldn't have been very good and when the oxygen level dropped, it had to be hard for the vertebrates coming out of the water," he says.
Ward and his colleagues tested this hypothesis by examining the breathing system of birds. They found that at sea level, birds breathe 30 percent more efficiently than mammals and at 5,000 feet in elevation birds are 200 percent more efficient.
According to Ward, dinosaurs possessed the ability to to run rings around their prey at higher altitudes.
Ward is also now of the opinion that the shape and design of the body may have been determined by respiratory efficiency in the past.