Changing the way we look at the world
Shape shifting dinosaurs

When is a Triceratops not a Triceratops?  
The answer is when it is a Torosaurus! It was once thought that Triceratops and Torosaurus were different creatures, but research published in 2010 caused a re-think. 

The research published by Scannella and Horner (2010) shows that the skull of the Triceratops changed shape quite dramatically as it grew. What were once thought to be two different types (genera) of dinosaur are in fact the same species. As Triceratops got older the shape of its skull changed to become that of what was (until now) called a Torosaurus. This is surprising because at first glance they are very different. Triceratops had three facial horns and a short, thick neck-frill with a saw-toothed edge. The Torosaurus also had three horns, though at different angles, and a much longer, thinner, smooth-edged frill with two large holes in it.  
How did they work out that these creatures are the same species? Dinosaur bones have growth lines (something like tree rings) and by counting these lines it is possible to estimate the age of the dinosaur when it died. By studying Triceratops skulls and nine Torosaurus skulls and counting the growth lines on each they were able to show that the skulls changed from Triceratops to Torosaurus as they got older. So in fact Torosaurus is an old Triceratops and the number of dinosaur species just got smaller. 
And this is not just an isolated case. It appears that a similar thing happens with Pachycephalosuarus, the juveniles of which were previously called Dracorex and Stygimoloch . 
This is also the case for that most famous of dinosaurs T. rex which is an “older version” of Nanotyrannus. 
This work has possible implications for evolutionary accounts of dinosaurs. Indeed it is possible that evolutionary transitions are nothing of the sort, they could represent different stages in the life of one species rather than an evolutionary divergence.