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Dubious extinct genus of dinosaurs

Trachodon (meaning "rough tooth") is a dubious genus of hadrosaurid dinosaur based on teeth from the Campanian age Upper Cretaceous Judith River Formation of Montana, U. S. It is a historically important genus with a convoluted taxonomy that has been all but abandoned by modern dinosaur paleontologists. Despite being used for decades as the iconic duckbill dinosaur, the material it is based on is composed of teeth from both duckbills and ceratopsids (their teeth have a distinctive double root), and its describer, Joseph Leidy, came to recognize the difference and suggested limiting the genus to what would now be seen as ceratopsid teeth.

In 1856, Joseph Leidy received fragmentary remains from the Judith River Formation, collected by Ferdinand Vandeveer Hayden. From these bones, he provided the first names for North American dinosaurs: Deinodon, Palaeoscincus, Trachodon, and Troodon (then spelled Troödon). The type species of Trachodon is T. mirabilis. The generic name is derived from Greek τραχυς, trakhys, "rough", and όδον, odon, "tooth", referring to the granulate inner surface of one of the teeth. The specific name means "marvelous" in Latin. Trachodon was based on ANSP 9260, seven unassociated teeth, one of which had double roots. With better remains from Hadrosaurus, he began to reconsider his taxonomy, and suggested, at least informally, that Trachodon should refer to the double rooted tooth, and the other teeth should be referred to Hadrosaurus. In the Bone Wars that followed, and their wake, the taxonomy of Trachodon and its relatives became increasingly confusing, but as new material was described from the Rocky Mountain region, Alberta, and Saskatchewan, later authors began progressively restricting the reach of this genus. By 1942, and the publication of the influential Lull Wright monograph on duckbills, its holotype was regarded as "typical of all the genera of hadrosaurian dinosaur", except for the roughened margin that gave it its name, and that they regarded as due to the tooth having not been used (p. 149). The name is no longer in use, except in historical discussions, and is considered a nomen dubium. In 1936, paleontologist Charles Sternberg compared the holotype teeth of Trachodon mirabilis to those of more completely known hadrosaurids and noted that they were most similar to those of lambeosaurines.

As a hadrosaurid, Trachodon would have been a large, bipedal/quadrupedal herbivore.