The mammillae (the cone-shaped structures in the mammillary layer which make up the base of each eggshell unit) are formed by wedge-shaped crystals.

[1] Cladistic analysis shows Montanoolithus to be maniraptoran eggs, more basal than troodontids, but more derived than oviraptorids.

[1][3] Maniraptorans are only represented at the Two Medicine formation by Troodon (whose eggs are already known), dromaeosaurs, and caenagnathids.

The nest was made from freshly deposited sand (perhaps near to a river), or in a poorly vegetated area.

[1] Montanoolithus is classified in its own oofamily, Montanoolithidae, which is related to the eggs of oviraptorids, troodontids, and birds.