Despite being used for decades as the iconicduckbill dinosaur, the material it is based on is composed of teeth from both duckbills andceratopsids (their teeth have a distinctive double root[3]), and its describer,Joseph Leidy, came to recognize the difference and suggested limiting the genus to what would now be seen as ceratopsid teeth.[2] Restricted to the duckbill teeth, it may have been alambeosaurine.[4]
In 1856, Joseph Leidy received fragmentary remains from the Judith River Formation, collected byFerdinand Vandeveer Hayden. From these bones, he provided the first names forNorth American dinosaurs:Deinodon,Palaeoscincus,Trachodon, andTroodon (then spelledTroödon).[1][5] Thetype species ofTrachodon isT. 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. Thespecific name means "marvelous" inLatin.
Trachodon was based on ANSP 9260, seven unassociated teeth, one of which had double roots. With better remains fromHadrosaurus, he began to reconsider his taxonomy, and suggested, at least informally, thatTrachodon should refer to the double-rooted tooth, and the other teeth should be referred toHadrosaurus.[6] In theBone Wars that followed, and their wake, the taxonomy ofTrachodon and its relatives became increasingly confusing,[2] with one author going so far as to sink all known hadrosaur species intoTrachodon except forClaosaurus agilis,[7] but as new material was described from theRocky Mountain region,Alberta, andSaskatchewan, later authors began progressively restricting the reach of this genus.[4][8]
By 1942, and the publication of the influential Lull-Wrightmonograph on duckbills, itsholotype 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).[9] The name is no longer in use, except in historical discussions, and is considered anomen dubium.[10][11][12]
In 1936, paleontologist Charles Sternberg compared the holotype teeth ofTrachodon mirabilis to those of more completely known hadrosaurids and noted that they were most similar to those of lambeosaurines.[4] It has been reported that paleontologistJohn R. Horner also found thatTrachodon teeth compare well with the teeth of lambeosaurines, specificallyCorythosaurus, though they also share similarities with the genusProsaurolophus.[13]
T. marginatus (nomen dubium) Lambe, 1902[18] (based on NMC 419, disassociated postcranial material; later made the type species of the genusStephanosaurus marginatus[19] and then referred toKritosaurus asKritosaurus marginatus,[20] which is not supported by later reviews.[11][12])
T. (Pteropelyx)selwyni (nomen dubium) Lambe, 1902[18] (based on NMC 290, a dentary with teeth, from the Dinosaur Park Formation of Alberta; too fragmentary to assign beyond Hadrosauridae)[11][12]
^abcLeidy, J. (1856). "Notice of remains of extinct reptiles and fishes, discovered by F. V. Hayden in the Bad Lands of the Judith River, Nebraska Territories."Proceedings of the Academy of Natural Science Philadelphia,8(25 March): 72–73.
^abcCreisler, B.S. (2007). Deciphering duckbills. in: K. Carpenter (ed.),Horns and Beaks: Ceratopsian and Ornithopod Dinosaurs. Indiana University Press: Bloomington and Indianapolis, 185–210.ISBN0-253-34817-X
^Hatcher, J.B., Marsh, O.C. and Lull, R.S. (1907).The Ceratopsia. Government Printing Office, Washington, D.C., 300 pp.ISBN0-405-12713-8
^abcSternberg, C.M. (1936). The systematic position ofTrachodon.Journal of Paleontology 10(7):652–655.
^Dodson, Peter (2009). "Dinosaurs in America – Joseph Leidy & the Academy of Natural Sciences".American Paleontologist.17 (2): 32.
^Leidy, J. (1868). Remarks on a jaw fragment ofMegalosaurus.Proceedings of the Academy of Natural Science Philadelphia 20:197–200.
^Hatcher, J.B. (1902). The genus and species of the Trachodontidae (Hadrosauridae, Claosauridae) Marsh.Annals of the Carnegie Museum 14(1):377–386.
^Gilmore, C.W. (1915). On the genusTrachodon.Science 41:658–660.
^Lull, R.S., and Wright, N.E. (1942). Hadrosaurian Dinosaurs of North America.Geological Society of America Special Paper 40:1–242.
^Coombs, Jr., W.P. (1988). The status of the dinosaurian genusDiclonius and the taxonomic utility of hadrosaurian teeth.Journal of Paleontology 62:812–818.
^abcdeWeishampel, D.B., and Horner, J.R. (1990). Hadrosauridae. In: Weishampel, D.B., Dodson, P., and Osmólska, H. (eds.).The Dinosauria. University of California Press:Berkeley, 534–561.ISBN0-520-24209-2
^abcdeHorner, J.R., Weishampel, D.B., and Forster, C.A. (2004). Hadrosauridae. In: Weishampel, D.B., Dodson, P., and Osmólska, H. (eds.).The Dinosauria (second edition). University of California Press:Berkeley, 438–463.ISBN0-520-06727-4
^Riabinin, A.N. (1925). A mounted skeleton of the gigantic reptileTrachodon amurense, nov. sp.Izvest. Geol. Kom. 44(1):1–12. [Russian]
^Riabinin, A.N. (1930).Mandschurosaurus amurensis, nov. gen., nov. sp., a hadrosaurian dinoasur from the Upper Cretaceous of Amur River.Mémoir II, Société Paléontologique de Russie. [Russian]
^Lydekker, R. (1888). Note on a new Wealden iguanodont and other dinosaurs.Quarterly Journal of the Geological Society of London 44:46–61.
^Marsh, O.C. (1897). Vertebrate fossils of the Denver Basin.U.S. Geological Survey, Monthly 27:473–527.
^abLambe, L.M. (1902). On Vertebrata of the mid-Cretaceous of the Northwest Territory. 2. New genera and species from the Belly River Series (mid-Cretaceous).Contributions to Canadian Paleontology 3:25–81.
^Lambe, L.M. (1914). On a new genus and species of carnivorous dinosaur from the Belly River Formation of Alberta, with a description of the skull ofStephanosaurus marginatus from the same horizon.Ottawa Naturalist 28:13–20.
^Gilmore, Charles W. (1924). "On the genusStephanosaurus, with a description of the type specimen ofLambeosaurus lambei, Parks".Canada Department of Mines Geological Survey Bulletin (Geological Series).38 (43):29–48.
