An order Ornithoscelida was originally proposed by Thomas Henry Huxley but later abandoned in favor of Harry Govier Seeley's division of Dinosauria into Saurischia and Ornithischia.

[6] In the beginning of the twenty-first century, improved descriptions of the early ornithischians Heterodontosaurus and Lesothosaurus vastly increased the available information on the origins of the Ornithischia.

This means that this node-based clade consists of the last common ancestor of the extant theropod Passer and the ornithischian Triceratops; and all its descendants.

The same study, when analysing a modified version of the original Baron et al. (2017) dataset, also found some support for the Phytodinosauria hypothesis when using certain types of analysis.

[8] The Ornithoscelida hypothesis has been challenged by a team of international researchers in November 2017, following a reworking of the original anatomical dataset from Baron et al. (2017).

With only minor adjustments made by Baron and colleagues in response, Ornithoscelida was found to be preferred over the traditional model once more.