Dysganus

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Dysganus is a dubious small “dinosaur”known only from teeth found in the Judith River Formation of Montana, from the Campanian stage of the Late Cretaceous (about 79–75 million years ago). The name means “rough enamel.”

Type species and other names
- Type species: Dysganus encaustus
- Other named species: D. bicarinatus, D. haydenianus, D. peiganus
- The teeth were first described by Edward Drinker Cope in 1876 during the Bone Wars. Cope thought the teeth came from a small herbivorous dinosaur related to Cionodon and Hadrosaurus. Each species is known only from a few detached teeth, likely from different individuals.

What the names mean
- Dysganus: rough enamel
- encaustus: burnt in (refers to the concave tip of the tooth)
- bicarinatus: two keels (on the teeth)
- haydenianus: named after Ferdinand V. Hayden
- peiganus: named after the Peigan Native Americans of Montana

What happened to the idea of Dysganus
- The fossils are just teeth, and they turned out to come from more than one kind of animal.
- In 1907, John Bell Hatcher showed the Dysganus teeth were a mix from hadrosaurids and ceratopsids, making the genus a chimera.
- Because the material is so mixed and incomplete, Dysganus is considered a nomen dubium (a dubious genus) and not a valid, separate dinosaur.
- The teeth that Cope described were from the Judith River Formation and are now kept at the American Museum of Natural History.

Context
- The Judith River Formation yielded many other fossils named during the Bone Wars, including large tyrannosaurids, hadrosaurs, and ceratopsians, many of which are also viewed with caution today.