Kritosaurus: the hadrosaur with a missing nose

Kritosaurus navajovius was a large plant-eating hadrosaur from late Campanian New Mexico, about 73.8–73.5 million years ago. Its name is familiar from pictures of a high, rounded “Roman nose”, but the key front part of the type skull is missing. That profile is a historical reconstruction, not a shape preserved in the fossil.

The genus is important because it shows how a small amount of damaged material can influence classification for decades. Re-examination has narrowed the fossils confidently assigned to Kritosaurus and separated it from similar hadrosaurids such as Gryposaurus.

The fossils support a recognisable hadrosaurid genus, especially through parts of the cheek and skull roof. They do not establish the outline of its snout or a complete body skeleton.

Quick facts

Name and discovery

Barnum Brown named Kritosaurus in 1910. The name is usually interpreted as “separated lizard”, referring to the arrangement of cheek bones he saw in the incomplete skull. A popular alternative, “noble lizard”, is not the best-supported explanation. The species name navajovius refers to the Navajo region where the fossil was found.

Brown collected the type specimen AMNH 5799 in 1904 in San Juan County, north-western New Mexico. Its source is now placed in the De-na-zin Member of the Kirtland Formation. The specimen preserves a substantial but damaged skull, lower jaws and a few other bones. The front of the snout and upper beak had already broken apart or been lost before excavation.

Early restorers filled the gaps by comparison with better-known duck-billed dinosaurs. Later mounts gave the animal a prominent convex nose resembling that of Gryposaurus. The restoration became influential in publications and museum displays, although the relevant nasal region of the Kritosaurus type is too incomplete to confirm that shape.

Classification and disputed names

Kritosaurus is an ornithopod in Hadrosauridae, within Saurolophinae and the tribe Kritosaurini. Its relationships are assessed from combinations of skull features, including the maxilla, jugal, temporal opening and the contribution of the frontal bone to the eye socket. No single broad, duck-billed outline is enough to identify a genus.

K. navajovius is the secure type species. A second proposed species has a less settled history. The skull first named Anasazisaurus horneri is treated by some researchers as Kritosaurus horneri, while others retain Anasazisaurus as a separate genus. Its short nasal crest should not automatically be added to the reconstruction of K. navajovius.

The New Mexican hadrosaur Naashoibitosaurus ostromi has also sometimes been folded into Kritosaurus, but many treatments keep it distinct. An older skull once assigned to K. navajovius has more recently been named Ahshislesaurus, further reducing the secure sample. These changes reflect comparisons among particular bones, not a simple count of every fossil once labelled “Kritosaurus”.

What the fossils preserve

AMNH 5799 contains the middle and rear portions of the skull, parts of the palate, both lower jaws and a small amount of postcranial material. The premaxillae and much of the nasal region are absent or fragmentary. Those are precisely the areas that would be needed to establish the animal’s external muzzle profile.

The surviving bones are adequate for recognising a combination of diagnostic characters, but not for measuring the whole animal. There is no securely associated complete vertebral column, full set of limbs or intact tail. The body shown in life restorations is therefore assembled by comparison with other hadrosaurids.

During the twentieth century, scattered fossils from Canada, the southern United States, Mexico and South America were assigned to Kritosaurus. Later revisions moved many Canadian specimens to Gryposaurus, recognised South American forms as separate genera, or left incomplete material as indeterminate hadrosaurids. Even one formation can preserve different animals at different times: members of the Kirtland Formation are separated by substantial intervals and should not be pooled without stratigraphic control.

Size and anatomy

Adult length is usually estimated at about 8–9 metres, with a mass around 3–4 tonnes. These are comparative estimates based on the skull and better-known relatives, not measurements of a complete Kritosaurus skeleton. The result changes with the analogue and body proportions selected.

The mouth had a broad, toothless beak in front of dense dental batteries. Rows of replacement teeth moved into use as older crowns wore down, producing a durable surface for cropping and grinding vegetation. The preserved maxilla is robust, and the cheek region has proportions useful for diagnosis. The temporal opening behind the eye is relatively tall and affects the slope of the rear skull roof.

By contrast, the snout cannot be reconstructed confidently. The type fossil does not prove a flat muzzle, a hooked “Roman nose” or a particular short crest. The deep trunk, powerful hind limbs, shorter weight-bearing forelimbs and long tail in reconstructions follow the general hadrosaurid plan. A facultatively bipedal gait is plausible by comparison with relatives, but has not been demonstrated from a complete Kritosaurus skeleton.

Habitat and feeding

The animal lived in southern Laramidia, the western landmass separated from eastern North America by the Western Interior Seaway. Rivers, floodplains and low wetlands accumulated the De-na-zin sediments. The climate was warm; conifers, flowering plants and ferns formed part of the regional vegetation. The wider setting belongs to the Cretaceous Period.

A broad beak could gather leaves and young shoots, while the dental batteries processed fibrous plant matter. Body posture would have changed feeding height: an animal on all fours could crop lower growth, and rearing onto its hind limbs may have extended its reach. No gut contents or coprolites securely tied to this genus identify a precise menu.

Other hadrosaurids, horned and armoured herbivores, and predatory theropods lived in the regional ecosystem. Their shared occurrence does not prove that particular individuals interacted. There is no direct evidence for Kritosaurus herd size, migration, nesting or parental care. Group behaviour known from some hadrosaurid bonebeds and trackways should not be transferred automatically to this genus; colour, calls and maximum speed are also unknown.

The Roman nose and other reconstructions

The famous Roman nose began with the restoration of a broken skull and comparison with Gryposaurus. Because the central nasal region of AMNH 5799 is damaged, the high curve is not confirmed by fossil bone. A cautious reconstruction should use a neutral profile or make the uncertainty clear.

Another outdated idea treated Kritosaurus as an older name for Gryposaurus. The genera were once combined, and images of one sometimes appeared under the other name. Later comparisons found enough cranial differences to recognise them separately; a distinctive Gryposaurus hook should not simply be copied onto Kritosaurus.

Old range maps made the genus appear to span much of the Americas, from Canada to Argentina. That broad distribution resulted from combining fossils of different ages and anatomy. The defensible range of K. navajovius is much narrower and centred on late Campanian deposits in New Mexico. The hadrosaurid family contains many better-represented genera, but comparisons do not turn their missing bones into direct evidence for this one.

Kritosaurus is a valid, distinctive saurolophine known mainly from an incomplete skull. Its value lies in the anatomical evidence and the history of correcting old assignments, not in a confidently known nose or a complete life reconstruction. The better-preserved Edmontosaurus offers a useful family comparison, not a substitute skeleton. See its profile alongside other ornithopods in the dinosaur catalogue.