大型恐龙为何不在热带地区生活

For more than 30 million years after dinosaurs¹ first appeared, they remained inexplicably² rare near the equator, where only a few small-bodied meat-eating dinosaurs made a living. The long absence at low latitudes³ has been one of the great, unanswered questions about the rise of the dinosaurs.

 

Now the mystery has a solution, according to scientists who pieced together a detailed⁴ picture of the climate and ecology more than 200 million years ago at Ghost Ranch⁵ in northern New Mexico, a site rich with fossils.

 

The findings, reported today in the journal Proceedings⁶ of the National Academy of Sciences (PNAS), show that the tropical climate swung wildly with extremes of drought and intense heat.

 

Wildfires swept the landscape during arid⁷ regimes and reshaped the vegetation available for plant-eating animals.

 

"Our data suggest it was not a fun place," says scientist Randall Irmis of the University of Utah.

 

"It was a time of climate extremes that went back and forth⁸ unpredictably. Large, warm-blooded dinosaurian⁹ herbivores weren't able to exist close to the equator--there was not enough dependable plant food."

 

The study, led by geochemist Jessica Whiteside, now of the University of Southampton, is the first to provide a detailed look at climate and ecology during the emergence¹⁰ of the dinosaurs.

 

Atmospheric¹¹ carbon dioxide levels then were four to six times current levels. "If we continue along our present course, similar conditions in a high-CO2 world may develop, and suppress low-latitude ecosystems," Irmis says.

 

"These scientists have developed a new explanation for the perplexing near-absence of dinosaurs in late Triassic [the Triassic was between 248 million and 205 million years ago] equatorial settings," says Rich Lane, program director in the National Science Foundation's (NSF) Division of Earth Sciences, which funded the research.

 

"That includes rapid vegetation changes related to climate fluctuations¹² between arid and moist climates and the resulting extensive wildfires of the time."

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