From sharks to giraffes, many of Earth’s biggest and most magnificent species are threatened with extinction. A new study of the fossil record indicates that once large vertebrates disappear, evolution cannot quickly restore them — for tens of millions of years, most animals remain small.

The study, published Thursday in Science, emerged from research carried out by Lauren Sallan, a paleontologist at the University of Pennsylvania.

As reported in New York Times on November 12, 2015.