HEXINLUSAURUS

One of the most confusing things, when digging back through dinosaur research, is the number of different names that certain critters have carried and the families to which they have been assigned. Unless you're an expert, it's hard to keep up! Hexinlusaurus, for example, was long thought to be a type of primitive ornithopod—specifically a hypsilophodontid—that He and Cai assigned to Yandusaurus as Yandusaurus multidens in 1983. But even then, some experts considered it to be a juvenile form of the name-bearer Yandusaurus hongheensis.

Scrutiny by Peng in 1992 led him to conclude that this specimen was a close relative of Agilisaurus, a genus he had already severed from the hypsilophodonts and reassigned to a group of primitive ornithischians known as fabrisaurids two years prior. In fact, he was convinced it was Agilisaurus, albeit a second species, which he named Agilisaurus multidens. After a stint as a possible species of the cerapod Othnielia, courtesy of Gregory Paul in 1996, it suffered the indignity of being informally referred to as "Proyandusaurus": a name lifted from a 1999 abstract by Fabien Knoll that should never have seen the light of day. Through all the chopping and changing, though, the species name multidens remained consistent, and it was still there when Paul Barrett and colleagues brought Hexinlusaurus multidens to its current resting place in 2005.

Hexinlusaurus was a small, bipedal, fleet-footed herbivore, and is now a recognised member of Neornithischia. Most of the still-valid dinosaurs to which Hexinlusaurus was previously linked are now all recognised neornithischians too, though none of them, nor Hexinlusaurus, belong to the clade's two main groups: Ornithopoda (iguanodonts and their relatives) or Marginocephalia (ceratopsians and pachycephalosaurs). By the by, "Fabrosauridae" and "Hypsilophodontidae" are no longer recognised families and have fallen out of use.