The name means "separated lizard" (referring to the arrangement of the cheek bones in an incomplete type skull), but is often mistranslated as "noble lizard" in reference to the presumed "Roman nose" [1] (in the original specimen, the nasal region was fragmented and disarticulated, and was originally restored flat).

In 1904, Barnum Brown discovered the type specimen (AMNH 5799) of Kritosaurus near the Ojo Alamo Formation, San Juan County, New Mexico, United States, while following up on a previous expedition.

[3] This synonymy was used through the 1920s (William Parks's designation of a Canadian species as Kritosaurus incurvimanus,[9] now considered a synonym of Gryposaurus notabilis[10]) and became standard after the publication of Richard Swann Lull and Nelda Wright's 1942 monograph on North American hadrosaurids.

The poorly known species Hadrosaurus breviceps (Marsh, 1889),[12] known from a dentary from the Campanian-age Judith River Formation of Montana, was also assigned to Kritosaurus by Lull and Wright,[11] but this is no longer accepted.

[13][14] By the late 1970s and early 1980s, Hadrosaurus had entered the discussion as a possible synonym of either Kritosaurus, Gryposaurus, or both, particularly in semi-technical "dinosaur dictionaries".

[15][16] David B. Norman's The Illustrated Encyclopedia of Dinosaurs, uses Kritosaurus for the Canadian material (Gryposaurus), but identifies the mounted skeleton of K. incurvimanus as Hadrosaurus.

This includes, for example, James Hopson's discussion of hadrosaur cranial ornamentation,[18] and the adaptation of this for the public in The Illustrated Encyclopedia of Dinosaurs.

[19] In 1984, Argentine paleontologist José Bonaparte and colleagues named Kritosaurus australis for hadrosaur bones from the late Campanian-early Maastrichtian Los Alamitos Formation of Rio Negro, Patagonia, Argentina.

The name was derived from the Anasazi, an ancient Native American people, and the Greek word sauros ("lizard").

[24] In 2002, specimen TxVP 41917-1, a partial left maxilla recovered from Bruja Canyon in Big Bend National Park, was assigned to Kritosaurus, as cf.

Twenty years later, it was discovered to contain a number of useful diagnostic traits that allow it to be described as a new taxon, and thus Malefica was named by Prieto-Márquez and Wagner (2023).

[13] Not all authors have agreed with this, Thomas E. Williamson in particular defending Horner's original interpretation,[4] and several subsequent studies recognized both distinct genera.

[27] This skeleton is about 20% larger than other known specimens, around 11 meters [36 ft] long, and with a distinctively curved ischium, and represents one of the largest known well-documented North American saurolophines.

[30][31] The type specimen of Kritosaurus navajovius is only represented by a partial skull and lower jaws, and associated postcranial remains.

[34] Based on the skull originally referred to Anasazisaurus, the form of the complete crest is that of a tab or flange of bone, from the nasals, that rises between and above the eyes and folds back under itself.

[27] Location and time separate Kritosaurus and the slightly older, primarily Canadian Gryposaurus, along with some cranial details.

[18] As a hadrosaurid, Kritosaurus would have been a large bipedal/quadrupedal herbivore, eating plants with a sophisticated skull that permitted a grinding motion analogous to chewing.

[38] The geographic range of Kritosaurus remains in North America was expanded by the discovery of bones from the late Campanian-age Aguja Formation of Texas, including a skull,[39][40] although this specimen was given its own genus name, Aquilarhinus, in 2019.