Tentative terrestrial reptile biostratigraphy estimates that the Eagle Basin fossils, which were preserved in red siltstone, belong to the Revueltian biozone of the mid to late Norian stage of the Triassic, 215-207 million years ago.

Dinosauromorph-like tibia and scapulae from the area may also belong to Kwanasaurus, though they have not been referred to the genus due to lacking any clear silesaurid features.

Five of the replacement pits at the midlength of the bone are set in a groove, a trait also present in Silesaurus and silesaurid skull material from the Ntawere Formation.

The front of the maxilla is similar to that of Lewisuchus and Silesaurus, with a triangular premaxillary facet and thick, sharp vomerine flange.

The ascending process of the maxilla is a thin, anteroposteriorly wide, and steeply-rising prong, and the antorbital fossa has a concave lower edge, both like Silesaurus.

This medial flange is unique to Kwanasaurus among silesaurids (and Triassic dinosauromorphs in general), and likely extended the maxilla's connection with the palate behind the vomer.

Isolated teeth are leaf-shaped, with coarse denticles, slightly flattened sides, and crown tips more than halfway towards the rear of the tooth.

[1] Like other silesaurids, Kwanasaurus has ankylothecodont tooth implantation, meaning the teeth are set in sockets but also fused to the surrounding bone.

This contrasts with Silesaurus and Technosaurus (which sometimes have several adjacent teeth replaced at once), but resembles the condition in some specimens of Sacisaurus, Diodorus, and Asilisaurus.

[1] A long and slender humerus is the only forelimb bone safely assigned to Kwanasaurus, based on its similarity to that of Silesaurus and Diodorus.

Kwanasaurus takes this trend further, lengthening the preacetabular process so that it projects further forwards than the pubic peduncle, an adaptation otherwise only seen in several lineages of dinosaurs among dinosauromorphs.

The codings for the taxon were based on both all the Eagle Basin silesaurid material as well as the dinosauromorph tibiae and scapulae which may additionally belong to it.

Here is the consensus cladogram (specifically the portion focusing on dinosauromorphs) after the removal of the three unstable taxa:[1] Lagerpeton chanarensis Dromomeron gregorii Dromomeron romeri Marasuchus lilloensis Dinosauria Lewisuchus/Pseudolagosuchus Asilisaurus kongwe Silesaurus opolensis Sacisaurus agudoensis Lutungutali sitwensis Diodorus scytobrachion Eucoelophysis baldwini Kwanasaurus williamparkeri Kwanasaurus was the northernmost and youngest silesaurid found in North America.

Its short, leaf-shaped, and heavily denticulated teeth were adapted for eating plants, a trait shared by several other advanced silesaurids.

This diet represents the culmination of a series of adaptations within Silesauridae, starting with carnivory in Lewisuchus (evidenced by recurved and finely serrated teeth), leading to omnivory and/or insectivory in Asilisaurus and Silesaurus (conical teeth with few serrations), and eventually the evolution of a specialized herbivorous diet in advanced sulcimentisaurians.

Kwanasaurus in particular had robust skull bones ornamented with ridges, indicating that it likely fed on tougher plants than other herbivorous silesaurids.

The timing of silesaurid dietary evolution mirrors the acquisition of herbivory in sauropodomorph dinosaurs, which diversified in southern and eastern portions of Pangea in the Norian stage.

The absence of herbivorous dinosaurs in the Chinle Formation may indicate that they had not yet colonized the northwestern region of Pangea that would eventually become North America.

Kwanasaurus was one of the silesaurids that was a part of this Norian herbivore guild, along with its relative Eucoelophysis (which lived in further south in New Mexico).