Hyotheridium is a possible Eutherian from the Late Cretaceous (?late Santonian–early Campanian) Djadochta Formation of Mongolia. It could be also be a Deltatheriid, although the fossil, a poorly preserved skull with the upper and lower jaws connected in a way that makes them hard to separate and to examine, makes it difficult to determine what it is.
Species taxanomy provided by GBIF Secretariat (2022). GBIF Backbone Taxonomy. Checklist dataset https://doi.org/10.15468/39omei accessed via GBIF.org on 2023-06-13; License: CC BY 4.0