Wannanosaurus

Wannanosaurus was an exceptionally small, primitive pachycephalosaur that lived in what is now Anhui Province, southeastern China, during the Late Cretaceous epoch. Reaching an estimated length of only 60 centimetres to one metre, it weighed roughly two to five kilograms, making it one of the smallest ornithischian dinosaurs known. The holotype specimen consists of a partial skull roof and fragmentary postcranial bones. Unlike classic dome-headed relatives such as Pachycephalosaurus, Wannanosaurus retained a relatively flat skull roof and large supratemporal fenestrae, showing that it branched off early from the ancestral pachycephalosaur tree. It was an agile bipedal animal that fed on low vegetation, seeds, and perhaps occasional insects. Its discovery showed that very basal pachycephalosaur lineages persisted alongside highly derived dome-headed species until near the close of the Mesozoic era.

It retained large cranial openings and a flat skull roof rather than a fully inflated dome.

Where and when

Wannanosaurus lived in the Late Cretaceous, from 72.1 to 66 million years ago (Maastrichtian age). Its remains come from China, in the Xiaoxiong Formation.

The numbers

Length 0.8 m (estimates run from 0.6 to 1 m). Mass about 3.2 kg. Hip height about 0.3 m. That is 0.5 human-lengths, or 0.07 of a double-decker bus. These are estimates from partial skeleton; fields marked estimated by the site are length, mass, first ma, last ma, hip height.

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