An illustration of dinosaurs—Edmontosaurus annectens (left), Tyrannosaurus rex, and Triceratops prorsus—on a floodplain from the late Maastrichtian, about 66 million years ago. A recent study suggests that unfavorable or undetected conditions for fossils may explain the low number and diversity of dinosaur fossils from the period before their extinction. (Photo credit: Davide Bonadonna)
Scientists say dinosaurs weren't in decline when an asteroid struck Earth and wiped them out. Instead, the idea that dinosaur diversity was declining before the asteroid hit 66 million years ago is likely based on faulty fossil data, according to a study that analyzed nearly 18 million years of fossil evidence.
Fossil evidence has long suggested that dinosaur numbers and diversity were declining before the asteroid impact at the end of the Cretaceous. Some researchers previously believed that this indicated that dinosaurs had already begun to go extinct before the catastrophic impact. However, this view has long been debated, with other researchers arguing that dinosaur diversity was normal at the time of their extinction.
“This question has been debated for over 30 years – were dinosaurs doomed and already extinct before the asteroid hit?” said lead author Chris Dean, a palaeontologist at University College London.
A new study published Tuesday (April 8) in the journal Current Biology suggests that the apparent rarity of dinosaurs before their extinction may simply be due to a poor fossil record.
The scientists analyzed data from about 8,000 fossils from North America dating back to the Campanian (83.6–72.1 million years ago) and Maastrichtian (72.1–66 million years ago), focusing on four families: Ankylosauridae, Ceratopsidae, Hadrosauridae, and Tyrannosauridae.
At first glance, their analysis showed that dinosaur diversity peaked about 76 million years ago and then declined until an asteroid strike wiped out the non-avian dinosaurs. This trend was even more pronounced in the 6 million years before the mass extinction, when the number of fossils of all four families in the geologic record declined.
A graphic illustration of a new study that shows the passage of time in North America, as well as the methods used to estimate fossil abundance.
However, as the researchers found out, there are no witnesses
Sourse: www.livescience.com
