monstersaurian squamates know from a single left dentary from the Early Cretaceous (?Albian) Ohyamashimo Formation of the Sasayama Group in Tamba City, Hyogo Prefecture, Japan.

[1] The type and only species is Morohasaurus kamitakiensis.

As of 2021, Ikeda et al. place this taxon a conferatur within Monstersauria based on general synapomorphies but without performing a phylogenetic analysis.

The unique characters described in the paper to distinguish Morohasaurus kamitakiensis as a valid species include "the sinuous posteroventral rim of the dentary with a large U-shaped upper notch and small V-shaped lower notch, posteroventral corner of intramandibular septum with a weakly pointed eminence projecting posteriorly, and unicuspid, curved trenchant teeth with distinct blade-like carinae on their mesial and distal sides without grooves or serrations."

If its presumed affinities are correct, Morohasaurus represents the oldest known monstersaurian to date.