Remember my post from last November about dinosaurs and metaplastic bone — about the revelation that because dinosaurs’ bones constantly reshaped themselves over their lives, dinosaurs that we thought were different species were, in fact, the same? New Scientist has an article on that subject this week, focusing on the revelation that the solid-frilled Triceratops and the open-frilled Torosaurus were the same animal. In fact, Torosaurus was the mature form of Triceratops: “As the animal aged, its horns changed shape and orientation and its frill became longer, thinner and less jagged. Finally it became fenestrated, producing the classic torosaurus form.”

The article notes two implications from this conclusion. First, this argues against a ceratopsian dinosaur using its frill for defense (this is nothing new: my understanding was that it existed to anchor jaw muscles). And second, this, combined with three other species being reassigned (two boneheads to Pachycephalosaurus, Nanotyrannus to T. rex), means that dinosaur diversity 65 million years ago, just before the mass extinction event, was even worse than we thought — and there weren’t that many known species from that period to begin with.

Via Robert J. Sawyer. Image credit: Triceratops and Torosaurus skulls from a diagram in Dinosaurs by W. D. Matthew (1915); public domain.