WANNANOSAURUS

The vast majority of pachycephalosaurs—the thick-skulled critters affectionately known as "head bangers"—hail from the Late Cretaceous of North America and Mongolia. So when the occasional outlier pops up in China, it always causes problems. Wannanosaurus was afforded the briefest of descriptions in 1977 by Lian-Hai Hou, who tagged it "primitive" because of its flat head and large fenestrae (skull windows), noting similarities to the basal ceratopsian Psittacosaurus. It soon drifted into obscurity, with only passing mention in the literature, and when R.J. Butler arrived to perform a thorough review of its remains in 2009, he found that some of them had gone AWOL. This kind of thing tends to hamper research somewhat.

Wannanosaurus is the only confirmed Asian "head banger" not bearing the customary "-cephale" suffix, which has led some paleontologists to lump it with one that does. For many moons, its tiny frame—less than a meter long with a thigh measuring just 8cm—was thought to be fully-grown, based on adulthood-heralding bone fusion as initially reported by Maryanska. But some experts now suspect it's merely a juvenile, possibly synonymous with the similarly flat-headed Homalocephale calathocercos from Mongolia's Nemegt Formation... which itself may just be a female morph of the high-domed Prenocephale prenes from the same area.