Bayannurosaurus perfectus was named by Xu et al. (2018) [Large non-hadrosauriform iguanodontian (
9 m long in presumable adults) with the following unique combination of features (*probable autopomorphies): denticulate anteromedial premaxillary oral margin with a shallow peripheral groove; occlusal margin of the premaxilla strongly ventrally offset; small, semicircular depression of the maxilla (indicative of the antorbital fossa), located a short distance from the maxillary ventral margin; markedly bifurcated anterior maxilla with an elevated anterodorsal process; elongate jugal contact surface of the maxilla entirely separated from the thickened ascending process; jugal bearing a relatively robust, slightly anteriorly curved postorbital process and a dorsally directed, strap-like posterodorsal process*; posterior neck of the jugal slightly dorsoventrally deeper than the anterior neck; supraoccipital excluded from the foramen magnum; posteriorly inclined coronoid process with a finger-shaped, anteroposteriorly narrow apex; tooth crowns with multiple weak mesiodistal wrinkles; labial surface of the maxillary crown with a prominent primary ridge and 1–2 parallel accessory ridges; each alveolus of the middle dentary holding one replacement tooth and one functional tooth; each dentary crown with a distally offset, weakly developed primary ridge; average height/width ratio of
1.85 for inactive crowns of the middle dentary; deeply opisthocoelous cervical centra; amphiplatyan centra along the dorsal series; posterior-most caudals with procoelous centra showing trapezoidal dorsal outlines; dorsal and ventral margins of the scapular blade that strongly diverge distally; deltopectoral crest anteriorly directed; carpals fused together to form a massive block; large, subconical ungual of manual digit I with a length/width ratio close to 1.0*; iliac preacetabular process horizontally oriented*; postacetabular process of the ilium having a strongly convex dorsal margin; distal blade of the pubis mediolaterally thin and deeply expanded dorsoventrally; ischial shaft straight; distal condyles of the femur strongly anteroposteriorly expanded; hoof-like unguals of manual and pedal digits III.]. Its type specimen is IMMNH PV00001, a skeleton (a nearly complete, semi-articulated skeleton, including the entire caudal series), and it is a 3D body fossil. Its type locality is Chulumiao, which is in an Aptian terrestrial horizon in the Bayingebi Formation of China.