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Divining dinosaur diversity.

Divining dinosaur diversity

How many types of dinosaurs lived during the 160-million-year span when these beasts rules the Earth? No one knows the true answer because many dinosaurs remain to be discovered and some may never come to light. Nonetheless, a paleontologist has tackled the question by studying the known groups, and his calculations point to a surprisingly low level of dinosaur diversity.

Researchers have described about 550 dinosaur genera over the last 170 years, with the rate of new discoveries accelerating greatly during the last two decades. Since 1970, scientists have identified about six new genera each year, or a total of 40 percent of all known dinosaurs, says Peter Dodson of the University of Pennsylvania in Philadelphia. Because many of the classifications are redundant, Dodson estimates that scientists currently know of only about 285 distinct genera. About 75 percent of those come from the United States, Mangolia, China, Canada, England and Argentina, he says,

Using these figures and an estimate of how long each genus survived, Dodson projects that only about 1,000 dinosaur genera ever existed. He expected a much larger number because these mammoth reptiles flourished for an extremely long span of time.

Careful estimates of dinosaur diversity can aid in studies of their extinction at the end of the Cretaceous period, about 65 million years ago. While some scientists think a meteorite impact killed the dinosaurs off suddenly, others say the extinctions occurred gradually over several million years due to climatic change or other factors. Dodson says his diversity figures do not support the gradual die-off theory.

In the future, he predicts, excavators will find most new dinosaur genera in Mongolia and Argentina, which hold promising reserves of unexplored rocks from the days of the dinosaurs. And he calculates that paleontologists will unearth almost all of the still-undiscovered genera within the next 200 years.

"By the year 2200, we'd better find a new occupation," he quips.
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Title Annotation:estimating the number of dinosaur genera
Author:Monastersky, Richard
Publication:Science News
Date:Oct 27, 1990
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