It is the replacement generic name for Alligatorium depereti, which was described in 1915 from the Montsec Lithographic Limestone quarry of Spain.

[1] Fossils found from this locality are from the Early Cretaceous, being Upper Berriasian-Lower Valanginian in age, belonging to the La Pedrera de Rúbies Formation[2] While many publications concerning atoposaurids after 1915 have included mentions of A. depereti, none has offered a redescription or revision of the species, though some recognized that great differences existed between it and other members of the genus.

[5][6] However, better preparation of the holotype specimen MGB 512, a nearly complete articulated skeleton embedded in a limestone matrix now housed in the Museu de Ciències Naturals de Barcelona,[7] allowed for a revision of the species in 1990 in which the name Montsecosuchus was first used.

Several characteristics of the skull including the presence of an ungrooved parietal-squamosal suture and a caudally projecting retroarticular process distinguish Montsecosuchus from these genera.

Both Montsecosuchus and Alligatorellus possess three sacral vertebrae; this may be a shared synapomorphy of the two genera.