It was discovered in the upper shale member of the Aguja Formation, among plant, bone, and clam fragments in a bed interpreted as the deposits of a small tributary channel.

[2] The first reports of Lambeosaurinae from the Aguja Formation of Texas were suggested in 1983 in the thesis of American paleontologist Kyle Davies, based upon the proportions of postcranial bones.

[3] While limb proportions have since been shown to not be distinctive of lambeosaurines, a later specimen was discovered in the field by a group from Texas Memorial Museum led by American paleontologist Thomas Lehman, at the "Dawson Creek" locality TMM 43681.

J. Browning discovered a partial maxilla and some vertebrae in the dark grey mudstone, with weathering to suggest that they had been transported by water from a disarticulated skeleton during a flooding event.

[1] The maxilla, TMM 43681-1, shows the first clear anatomy of a hadrosaurid from Big Bend, and displayed a diagnostic downturned snout leading Lehman and Jonathan Wagner to describe it as the new taxon Angulomastacator daviesi in 2009.