They suggest that the domes are actually autochthonous, or possibly parautochthonous – that pachycephalosaurs lived in alluvial and coastal lowlands, closer to where their remains were fossilised than previously thought.
This new hypothesis may not be popular – the 'Transport Hypothesis' has been around since the 1930's. And unlike the 'Transport Hypothesis', it doesn't quite explain why there are many more dome skulls preserved than the rest of the skeleton. But just because an idea may not be popular, does not mean it is incorrect. I look forward to seeing how the rest of the scientific community responds to the hypothesis proposed in this paper.
Mallon, J.C., Evans, D.C. 2014. Taphonomy and habitat preference of North American pachycephalosaurids (Dinosauria, Ornithischia). Lethaia, DOI: 10.1111/let.12082.