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Description
Illustrated by the talented Sheather888.

The Late Paleocene fossil record of Asia has thrown up a number of surprises. The most significant of these are several small, basal dinosaurs that almost seem to be relics lost in time. These include a small relative of Avimimus, the very basal Ceratopsian Plenoceratops mirabilis and the tiny, 1m long Pachycephalosaur Mengosaurus neimongolensis (as shown in the image above). This trend of small, basal dinosaurs suddenly turning up in unexpected places is certainly not without precedent. The discovery of Mahakala omnogovae, cited as the most basal of all Dromaeosaurs, in Campanian deposits and the presence of the mysterious Marginocephalian Micropachycephalosaurus in similar Late Cretaceous rocks demonstrates just how patchy our knowledge of ancient faunas really is at present.

Phylogenetic studies have come to the conclusion that Mengosaurus (along with the similarly basal Cretaceous Wannanosaurus) is among the most basal of all Pachycephalosaurs. Indeed, the thickened dome present on the skulls of more derived Pachycephalosaurs is completely absent. Instead, the skull of M. neimongolensis shows only a slight thickening and was most likely used for display. Its teeth were small, sharp and rather unspecialized, perhaps indicating a partially omnivorous diet. Like other basal Pachycephalosaurs, the premaxillary teeth are enlarged and blade-like, very different from the much smaller, leaf-shaped teeth of the maxilla. However, perhaps the most interesting fact concerning Mengosaurus is that it lies at the base of a highly diverse lineage that would later become one of the premier groups of herbivorous dinosaurs later in the Cenozoic: the Ankylotarsiformes.

Description
Illustrated by the talented Sheather888.

The Late Paleocene fossil record of Asia has thrown up a number of surprises. The most significant of these are several small, basal dinosaurs that almost seem to be relics lost in time. These include a small relative of Avimimus, the very basal Ceratopsian Plenoceratops mirabilis and the tiny, 1m long Pachycephalosaur Mengosaurus neimongolensis (as shown in the image above). This trend of small, basal dinosaurs suddenly turning up in unexpected places is certainly not without precedent. The discovery of Mahakala omnogovae, cited as the most basal of all Dromaeosaurs, in Campanian deposits and the presence of the mysterious Marginocephalian Micropachycephalosaurus in similar Late Cretaceous rocks demonstrates just how patchy our knowledge of ancient faunas really is at present.

Phylogenetic studies have come to the conclusion that Mengosaurus (along with the similarly basal Cretaceous Wannanosaurus) is among the most basal of all Pachycephalosaurs. Indeed, the thickened dome present on the skulls of more derived Pachycephalosaurs is completely absent. Instead, the skull of M. neimongolensis shows only a slight thickening and was most likely used for display. Its teeth were small, sharp and rather unspecialized, perhaps indicating a partially omnivorous diet. Like other basal Pachycephalosaurs, the premaxillary teeth are enlarged and blade-like, very different from the much smaller, leaf-shaped teeth of the maxilla. However, perhaps the most interesting fact concerning Mengosaurus is that it lies at the base of a highly diverse lineage that would later become one of the premier groups of herbivorous dinosaurs later in the Cenozoic: the Ankylotarsiformes.