A new analysis challenges the idea that dinosaur diversity boomed at the same time flowering plants began taking root across the planet. Researchers have found evidence that the great beasts responded little if at all to this influx of flora. Some experts doubt this conclusion, but if confirmed, the findings might require paleontologists to rethink dino history.
The Cretaceous period, which lasted from 145 million years ago to 65 million years ago, was a golden age of evolution. It saw the diversification of pollinating insects such as bees, butterflies, and moths. New forms of lizards, crocodiles, and snakes appeared, as did many of the ancestors of modern groups of birds and mammals. The Cretaceous also saw the explosion of angiosperms, or flowering plants. By the beginning of the period, dinosaurs had been around for more than 85 million years, but some researchers have suggested that the spread of flowers sparked a surge in dinosaur diversity, with many new species evolving to feast on the green bounty--or to devour the plant-eaters.
A beguiling prospect, but not one necessarily supported by the fossil record. At least, that's what a European team claims after performing a detailed computer analysis of dinosaur diversity through time. The researchers found that some of the evidence for rising dino diversity in the Cretaceous period came from sampling bias; more fossils of different species are available from the period than from earlier periods--a factor that could be due to chance. When they corrected for this bias, they found that instead of mirroring the evolutionary expansion of angiosperms, dinosaur diversity peaked 85 million to 55 million years earlier, during the early Jurassic period. In fact, the team reports in an upcoming issue of the Proceedings of the Royal Society B, there seems to be no correlation between dino diversity and the proliferation of flowering plants, and there is scant fossil evidence linking angiosperms to the dino diet.
But the researchers might be missing an important point, says paleontologist Charles Marshall of Harvard University. Instead of expecting an explosion of dinosaur diversity corresponding to the rise of angiosperms, he says, it's possible the plants prevented a decline in the rate of diversification. "The data are actually compatible with that conclusion," he says. Marshall adds that confirmation of the researchers' findings will depend on the collection of more evidence about dino diet in the Cretaceous, because right now "we don't know much about what they ate."