The discovery of Hesperonychus was a long and tangled quest. One day, I was sorting through some microvertebrates from the Lance Formation, really old stuff, collected by Marsh during the Yale expeditions to Wyoming back in the late 1800s. I pulled out this little toe bone- it was virtually identical to a bone from the second toe- the one that bears the killer claw- of the large dromaeosaur Deinonychus, which was actually a few cases away in the same collections. But this one was from a small animal, about the size of a cat.

Pentaceratops aquilonius is another of these museum discoveries- I was rummaging around in the Canadian Museum of Nature, looking for material of Mojoceratops, and ran across some frill pieces from the Manyberries area of southeastern Alberta. Wann Langston described the animal in 1959 and noted (correctly) that it most closely resembled Anchiceratops compared to the ceratopsian material that had been described. In fact, it was far more similar to Pentaceratops.

Texacephale langstoni is a small pachycephalosaur from Texas. Pachycephalosaurs are the so-called 'bone-headed' dinosaurs; their skulls are capped by a thick mass of bone that forms a sort of helmet over the top of the head. Only a few of them were previously known from Texas, all pretty scrappy.

Judiceratops tigris is a horned dinosaur from the Campanian of the Judith River Formation in Montana. It's a reasonably common animal there- four specimens are known- but unfortunately all of them are highly incomplete. Never the less, there is enough of the parietal- the diagnostic bit of the animal- to show that it's a new species. The back of the frill is broadly arched and has very low hornlets; the hornlets on the side of the frill become much larger towards the front, with large, ear-shaped hornlets at the front of the squamosals.

While writing up Mojoceratops, something strange happened doing the background research. Reading up other species, its relative Pentaceratops seemed to be a bizarrely variable animal. Most of the Pentaceratops skulls looked pretty similar to each other, showing pretty much the range of variation you’d expect in the skulls of a dinosaur species. But one skull was a massive outlier. It didn’t look at all like the others.

I ran across the first skull in the basement of the American Museum of Natural History. At the time, I was looking for evidence of T. rex feeding, traces, as part of the T. rex cannibalism paper. I saw this beautiful ceratopsian frill, and recognized it as the type of thing that was pretty common in Dinosaur Park. And just out of curiosity I was wondering what species it was- and I realized, I didn't know.