Pachycephalosaurus
As a Pachycephalosaurus you would carry one of the thickest skulls of any known dinosaur – a dome of solid bone up to about a quarter of a metre deep – and the open question of whether you ever head-butted anyone.
A head like a helmet
Pachycephalosaurus wyomingensis lived about 68–66 million years ago in western North America, alongside Triceratops and Tyrannosaurus. It was a bipedal plant-eater about 4.5 metres long and perhaps 350–450 kilograms, though it is known mainly from skulls, so body estimates are uncertain.
The domed skull roof reached about 25 centimetres thick and was ringed with knobs and short spikes at the back and on the snout. It was named in 1943, but its skull had been known since the 1930s. Its teeth were small and ridged, suited to leaves, seeds and fruit, though some researchers suspect an omnivorous diet.
To butt or not to butt
The classic image shows two males charging head-first like rams. Critics have pointed out that a rounded dome would glance off another dome and that the neck may not have been built for such impacts. Others suggested flank-butting instead.
Evidence has since shifted towards some form of combat. A 2013 study found lesions on many pachycephalosaur domes consistent with healed injuries, and studies of the bone’s internal structure suggest it could absorb impacts. Whether you would hit rivals head-on, from the side or both remains open.
One species, three names?
In 2009 Jack Horner and Mark Goodwin argued that two other dome-headed dinosaurs from the same rocks, Dracorex and Stygimoloch, were young Pachycephalosaurus. In their view, the skull went from spiky and flat to smooth and domed with age. This idea has gained wide support, though not every researcher agrees. If it is right, you would grow up looking like a dragon and end up looking like a bowling ball.
