Polyonax (meaning "master over many") was a genus of ceratopsid dinosaur from the late Maastrichtian-age Upper Cretaceous Denver Formation of Colorado, United States. Founded upon poor remains, it is today regarded as a dubious name.
History
During an 1873 trip through the western US, paleontologist and naturalist Edward Drinker Cope collected some fragmentary dinosaurian material which he soon named as a new genus. Catalogued today as AMNH FR 3950, the type material included three dorsal vertebrae, limb bone material, and what are now known to be horn cores, from a subadult individual. Although it was briefly mixed up with hadrosaurs, and even considered to be a possible synonym of Trachodon, it was recognized as a horned dinosaur in time for the first monograph on horned dinosaurs (1907), wherein it was regarded as based on indeterminate material. Today, the name is used as little more than a historical curiosity, as it dates from a time before horned dinosaurs were known to exist. The most recent review listed it as an indeterminate ceratopsid.
It has sometimes been listed as a synonym of Agathaumas, or Triceratops.
Paleobiology
As a ceratopsid, Polyonax would have been a large, quadrupedal herbivore, with brow and nasal horns and a neck frill.