, who initially studied Proceratosaurus, originally thought it to be an ancestor of the Late JurassicCeratosaurus, due to the similarity of their nasal crests. Later study during the 1930s by Friedrich von Huene supported this interpretation, and Huene thought both dinosaurs represented members of the group Coelurosauria. It was not until the late 1980s, after Ceratosaurus had been shown to be a much more primitive theropod and not a coelurosaur, that the classification of Proceratosaurus was again re-examined. Gregory S. Paul suggested that it was a close relative of Ornitholestes, again mainly due to the crest on the nose. Paul considered both Proceratosaurus and Ornitholestes to be neither ceratosaurs nor coelurosaurs, but instead primitive allosauroids. Furthermore, Paul considered the much larger dinosaurPiveteausaurus to be the same genus as Proceratosaurus, making Piveteausaurus a junior synonym. However, no overlapping bones between the two had yet been exposed from the rock around their fossils, and future study showed that they were indeed distinct. Several phylogenetic studies in the early 21st century finally found Proceratosaurus to be a coelurosaur, only distantly related to the ceratosaurids and allosauroids, though one opinion published in 2000 considered Proceratosaurus a ceratosaurid without presenting supporting evidence. Phylogenetic analyses by Thomas R. Holtz, Jr. in 2004 also placed Proceratosaurus among the coelurosaurs, though with only weak support, and again found an close relationship with Ornitholestes. The first major re-evaluation of Proceratosaurus and its relationships was published in 2010 by Oliver Rauhut and colleagues. Their study concluded that Proceratosaurus was in fact a coelurosaur, and moreover a tyrannosauroid, a member of the lineage leading to the giant tyrannosaurs of the Late Cretaceous. Furthermore, they found that Proceratosaurus was most closely related to the Chinese tyrannosauroid Guanlong. They named the clade containing these two dinosaurs the Proceratosauridae, defined as all theropods closer to Proceratosaurus than to Tyrannosaurus, Allosaurus, Compsognathus, Coelurus, Ornithomimus, or Deinonychus. Below is a cladogram by Loewen et al. in 2013.
