Few topics in science spark such fascination as the extinction
of dinosaurs about 65 million years ago, at the end of the
Cretaceous epoch. An asteroid impact and massive volcanism were
apparently to blame. But were dinosaurs already in decline
before those catastrophes? New research suggests that the
picture was complex, and that the answer is “yes,” at least for
some groups of dinosaurs. Paleontologist Stephen L. Brusatte of
the American Museum of Natural History in New York City and
three colleagues used a novel approach to explore this question.
Instead of examining trends in taxonomic diversity by counting
dinosaur species or genera, a method fraught with problems
because of the unevenness of the fossil record, the researchers
performed a quantitative analysis of “morphological
disparity”—the variability of body structure within a certain
group of animals. “Because skeletal anatomy is closely tied to
diet, ecology, and behavior, it is often thought that disparity
is a more biologically meaningful measure