According to the going theory, a six-mile-wide asteroid slammed into the Yucatán Peninsula 65 million years ago, throwing enough dust up into the atmosphere to dim the sun for years, killing off green plants and triggering a famine that wiped out all the dinosaurs in the geologic blink of an eye.
Not so fast, says U.S. Geological Survey geologist emeritus James Fassett. A few years ago, Fassett’s colleagues were digging in a fossil-rich area of New Mexico when they uncovered the four-foot-long fossilized thighbone of a duck-billed, plant-eating hadrosaur in a sandstone cliff. When Fassett dated the bone to half a million years or so after the dinosaurs’ supposed mass extinction, most paleontologists dismissed his find as a meaningless anomaly or a mistake. Now Fassett has examined 30 more dinosaur fossils in the same rock formation and completed a more extensive analysis of the surrounding environment, taking into account paleomagnetism, fossil leaves, pollen, spores, and the geochemistry of the area. “There’s no longer any question that dinosaurs in the area survived the asteroid impact event, finally becoming extinct about a million years later,” he says.
If Fassett is right, either a small group of dinosaur holdouts miraculously survived the catastrophe that killed their brethren, or possibly the K-T asteroid impact wasn’t nearly as deadly as some have claimed. The fossil record shows that lots of animals weathered the impact, including most mammals and birds, as well as lizards and amphibians. So why not some dinosaurs? “These dinosaurs could have survived in the Far North where the impact’s devastation was less, and then eventually they migrated back down south over time,” Fassett says. “Or it’s possible eggs may have survived the initial impact to hatch later and grow.”