Nopcsa, who found that Paranthodon best resembled a stegosaurid (before the group was truly defined). Coombs (1978) did not follow Nopcsa's classification, keeping Paranthodon as an ankylosaurian, like Broom, although he only classified it as Ankylosauria incertae sedis. A subsequent review by Galton and Coombs in 1981 instead confirmed Nopcsa's interpretation, redescribing Paranthodon as a stegosaurid from the Lower Cretaceous. Paranthodon was distinguished from other stegosaurs by a long, wide, posterior process of the premaxilla, teeth in the maxilla with a very large cingulum, and large ridges on the tooth crowns. Not all of these features were considered valid in a 2008 review of Stegosauria, with the only autapomorphy found being the possession of a partial second bony palate on the maxilla. Multiple phylogenetic analyses have placed Paranthodon in Stegosauria, and often in Stegosauridae. A 2010 analysis including nearly all species of stegosaurians found that Paranthodon was outside Stegosauridae, and in a polytomy with Tuojiangosaurus, Huayangosaurus, Chungkingosaurus, Jiangjunosaurus, and Gigantspinosaurus. When the latter two genera were removed, Paranthodon grouped with Tuojiangosaurus just outside Stegosauridae, and Huayangosaurus grouped with Chungkingosaurus in Huayangosauridae. An elaboration upon this analysis was published in 2017 by Susannah Maidment and Thomas Raven, and it resolved relationships within Stegosauria much more. All taxa were remained included, and Paranthodon grouped with Tuojiangosaurus, Huayangosaurus and Chunkingosaurus as the most basal true stegosaurians. The position of Alcovasaurus was uncertain, and further work could change the result. Below is the analysis. Other analyses have found Paranthodon closely related to Tuojiangosaurus, Loricatosaurus, and Kentrosaurus within Stegosaurinae. Even though phylogenetic analyses recognise Paranthodon as a stegosaurid, the type material bears no synapomorphies of Stegosauria. The material is likely of stegosaurian nature, and phylogenies by many authors have found it to be within the group. Paleoecology The Kirkwood Formation is in South Africa, and many fossils of different species and genera have been discovered in it, with Paranthodon being the first uncovered. The formation is of a Late Jurassic to Early Cretaceous age, with the oldest deposits from the Tithonian, about 145.5 million years ago, and the youngest rocks being from the Valanginian, about 130 million years ago. The specific vertebrate-bearing portion of the formation is approximately level with the upper region of the Sundays River Formation, which has been dated to 139 to 131 mya based on microfossils. A large variety of different animal groups have been found in the formation, including dinosaurs,