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.[1] It is a historically important genus with a convoluted taxonomy that has been all but abandoned by modern dinosaur paleontologists.[2]

Despite being used for decades as the iconic duckbill dinosaur per antonomasia the material it is based on is composed of teeth from both duckbills and ceratopsids (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 a lambeosaurine.[4]

Temporal range: Late Cretaceous, 77 Ma
Trachodon mirabilis
Illustration of the isolated teeth
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Clade: Dinosauria
Order: Ornithischia
Suborder: Ornithopoda
Family: Hadrosauridae
Genus: Trachodon
Leidy, 1856
T. mirabilis
Binomial name
Trachodon mirabilis
Leidy, 1856

Diclonius mirabilis (Leidy, 1856)

History and classification

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 last being the only name still in use.[1][5] 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.[6] In the Bone Wars that followed, and their wake, the taxonomy of Trachodon and its relatives became increasingly confusing,[2] with one author going so far as to sink all known hadrosaur species into Trachodon except for Claosaurus agilis,[7] but as new material was described from the Rocky Mountain region, Alberta, and Saskatchewan, later authors began progressively restricting the reach of this genus.[4][8]

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).[9] The name is no longer in use, except in historical discussions, and is considered a nomen dubium.[10][11][12]

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.[4] It has been reported that paleontologist John R. Horner also found that Trachodon teeth compare well with the teeth of lambeosaurines, specifically Corythosaurus, though they also share similarities with the genus Prosaurolophus.[13]


Numerous species have been referred to this genus, mostly before World War I. Only those originally named as a species of Trachodon are considered here.

Type species: T. mirabilis Leidy, 1856[1]

Other species:


As a hadrosaurid, Trachodon would have been a large, bipedal/quadrupedal herbivore.[12]

See also


  1. ^ a b c Leidy, J. (1856). "Notice of remains of extinct reptiles and fishes, discovered by Dr. F. V. Hayden in the Bad Lands of the Judith River, Nebraska Territories." Proceedings of the Academy of Natural Science Philadelphia, 8(March 25): 72-73.
  2. ^ a b c Creisler, B.S. (2007). Deciphering duckbills. in: K. Carpenter (ed.), Horns and Beaks: Ceratopsian and Ornithopod Dinosaurs. Indiana University Press: Bloomington and Indianapolis, 185-210. ISBN 0-253-34817-X
  3. ^ Hatcher, J.B., Marsh, O.C. and Lull, R.S. (1907). The Ceratopsia. Government Printing Office, Washington, D.C., 300 pp. ISBN 0-405-12713-8
  4. ^ a b c Sternberg, C.M. (1936). The systematic position of Trachodon. Journal of Paleontology 10(7):652-655.
  5. ^ Dodson, Peter (2009). "Dinosaurs in America – Joseph Leidy & the Academy of Natural Sciences". American Paleontologist. 17 (2): 32.
  6. ^ Leidy, J. (1868). Remarks on a jaw fragment of Megalosaurus. Proceedings of the Academy of Natural Science Philadelphia 20:197-200.
  7. ^ Hatcher, J.B. (1902). The genus and species of the Trachodontidae (Hadrosauridae, Claosauridae) Marsh. Annals of the Carnegie Museum 14(1):377-386.
  8. ^ Gilmore, C.W. (1915). On the genus Trachodon. Science 41:658-660.
  9. ^ Lull, R.S., and Wright, N.E. (1942). Hadrosaurian Dinosaurs of North America. Geological Society of America Special Paper 40:1-242.
  10. ^ Coombs, Jr., W.P. (1988). The status of the dinosaurian genus Diclonius and the taxonomic utility of hadrosaurian teeth. Journal of Paleontology 62:812-818.
  11. ^ a b c d e Weishampel, 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. ISBN 0-520-24209-2
  12. ^ a b c d e Horner, 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. ISBN 0-520-06727-4
  13. ^ Olshevsky, G. (1997), "Re: Ye Olde Duckbill Dinosaur", discussion group, The Dinosaur Mailing List, 8 August 1997. Accessed 6 April 2013.
  14. ^ Riabinin, A.N. (1925). A mounted skeleton of the gigantic reptile Trachodon amurense, nov. sp. Izvest. Geol. Kom. 44(1):1-12. [Russian]
  15. ^ 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]
  16. ^ Lydekker, R. (1888). Note on a new Wealden iguanodont and other dinosaurs. Quarterly Journal of the Geological Society of London 44:46-61.
  17. ^ Marsh, O.C. (1897). Vertebrate fossils of the Denver Basin. U.S. Geological Survey, Monthly 27:473-527.
  18. ^ a b Lambe, 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.
  19. ^ 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 of Stephanosaurus marginatus from the same horizon. Ottawa Naturalist 28:13-20.
  20. ^ Gilmore, Charles W. (1924). "On the genus Stephanosaurus, with a description of the type specimen of Lambeosaurus lambei, Parks". Canada Department of Mines Geological Survey Bulletin (Geological Series). 38 (43): 29–48.

Aralosaurini is a tribe of basal lambeosaurine hadrosaurs endemic to Eurasia. It currently contains Aralosaurus (from the Aral sea of Kazakhstan) and Canardia (from Toulouse, Southern France).


Brachylophosaurini is a tribe of saurolophine hadrosaurs with known material being from N. America and potentially Asia. It contains at least four taxa; Acristavus (from Montana and Utah), Brachylophosaurus (from Montana and Alberta), Maiasaura (also from Montana), and Probrachylophosaurus (also from Montana). A hadrosaur from the Amur river, Wulagasaurus, might be a member of this tribe, but this is disputed. The group was defined by Terry A. Gates and colleagues in 2011.The clade Brachylophosaurini was defined as "Hadrosaurine ornithopods more closely related to Brachylophosaurus, Maiasaura, or Acristavus than to Gryposaurus or Saurolophus".


Canardia is an extinct genus of aralosaurin lambeosaurine dinosaur known from the Late Cretaceous Marnes d’Auzas Formation (late Maastrichtian stage) of Toulouse, Haute-Garonne Department, southern France. The type species Canardia garonnensis was first described and named by Albert Prieto-Márquez, Fabio M. Dalla Vecchia, Rodrigo Gaete and Àngel Galobart in 2013.


Edmontosaurus ( ed-MON-tə-SAWR-əs) (meaning "lizard from Edmonton") is a genus of hadrosaurid (duck-billed) dinosaur. It contains two known species: Edmontosaurus regalis and Edmontosaurus annectens. Fossils of E. regalis have been found in rocks of western North America that date from the late Campanian stage of the Cretaceous Period 73 million years ago, while those of E. annectens were found in the same geographic region but in rocks dated to the end of the Maastrichtian stage of the Cretaceous, 66 million years ago. Edmontosaurus was one of the last non-avian dinosaurs, and lived alongside dinosaurs like Triceratops, Tyrannosaurus, Albertosaurus and Pachycephalosaurus shortly before the Cretaceous–Paleogene extinction event.

Edmontosaurus included some of the largest hadrosaurid species, measuring up to 12 metres (39 ft) long and weighing around 4.0 metric tons (4.4 short tons). Evidence does exist in the form of two fossilized specimens housed at the Museum of the Rockies for an even greater maximum size of 15 m (49 ft) and weighing 9.07 metric tons (10.00 short tons) for Edmontosaurus annectens. Several well-preserved specimens are known that include not only bones, but in some cases extensive skin impressions and possible gut contents. It is classified as a genus of saurolophine (or hadrosaurine) hadrosaurid, a member of the group of hadrosaurids which lacked large, hollow crests, instead having smaller solid crests or fleshy combs.The first fossils named Edmontosaurus were discovered in southern Alberta (named after Edmonton, the capital city), in the Horseshoe Canyon Formation (formerly called the lower Edmonton Formation). The type species, E. regalis, was named by Lawrence Lambe in 1917, although several other species that are now classified in Edmontosaurus were named earlier. The best known of these is E. annectens, named by Othniel Charles Marsh in 1892; originally as a species of Claosaurus, known for many years as a species of Trachodon, and later as Anatosaurus annectens. Anatosaurus and Anatotitan are now generally regarded as synonyms of Edmontosaurus.

Edmontosaurus was widely distributed across western North America. The distribution of Edmontosaurus fossils suggests that it preferred coasts and coastal plains. It was a herbivore that could move on both two legs and four. Because it is known from several bone beds, Edmontosaurus is thought to have lived in groups, and may have been migratory as well. The wealth of fossils has allowed researchers to study its paleobiology in detail, including its brain, how it may have fed, and its injuries and pathologies, such as evidence for tyrannosaur attacks on a few edmontosaur specimens.

Edmontosaurus annectens

Edmontosaurus annectens (meaning "connected lizard from Edmonton) is a species of flat-headed or saurolophine hadrosaurid ornithopod dinosaur (a "duck-billed dinosaur") from the very end of the Cretaceous Period, in what is now North America. Remains of E. annectens have been preserved in the Frenchman, Hell Creek, and Lance Formations. All of these formations are dated to the late Maastrichtian stage of the Late Cretaceous Period, representing the last three million years before the extinction of the dinosaurs (between 68 and 66 million years ago). Also, E. annectens is also from the Laramie Formation, and magnetostratigraphy suggests an age of 69-68 Ma for the Laramie Formation. Edmontosaurus annectens is known from numerous specimens, including at least twenty partial to complete skulls, discovered in the U.S. states of Montana, South Dakota, North Dakota, Wyoming and Colorado and the Canadian province of Saskatchewan. It was a large animal, up to approximately 12 metres (39 ft), potentially up to 15 m (49 ft) in length, with an extremely long and low skull. E. annectens exhibits one of the most striking examples of the "duckbill" snout common to hadrosaurs. It has a long taxonomic history, and specimens have at times been classified in the genera Diclonius, Trachodon, Hadrosaurus, Claosaurus, Thespesius, Anatosaurus and Anatotitan, before being grouped together in Edmontosaurus.

Edmontosaurus mummy AMNH 5060

The Edmontosaurus mummy AMNH 5060 is an exceptionally well-preserved fossil of a dinosaur in the collection of the American Museum of Natural History (AMNH). Discovered in 1908 in the United States near Lusk, Wyoming, it was the first dinosaur specimen found to include a skeleton encased in skin impressions from large parts of the body. It is ascribed to the species Edmontosaurus annectens (originally known as Trachodon annectens), a hadrosaurid ("duck-billed dinosaur"). The mummy was found by fossil hunter Charles Hazelius Sternberg and his three sons in the Lance Formation. Although Sternberg was working under contract to the British Museum of Natural History, Henry Fairfield Osborn of the AMNH managed to secure the mummy. Osborn described the fossil in detail in 1912, coining the name "dinosaur mummy" for it – several dinosaur mummies of similar preservation have been discovered since then. This specimen has considerably influenced the scientific conception of hadrosaurids. Skin impressions found in between the fingers were once interpreted as interdigital webbing, bolstering the now-rejected perception of hadrosaurids as aquatic animals, a hypothesis that remained unchallenged until 1964. Today, the mummy is considered one of the most important fossils of the AMNH.

The mummy was discovered lying on its back, its neck twisted backwards and its forelimbs outstretched. The skeleton is complete save the tail, hind feet, and the hind portion of the pelvis. All bones are preserved unflattened and still connected to each other. Almost two thirds of the skin is preserved. Delicate for the size of the animal, the skin includes two different types of non-overlapping scales that were between 1 and 5 inches (25 and 127 millimetres) in diameter. In contrast to other similar dinosaur mummies, the skin of AMNH 5060 was tightly attached to the bones and partially drawn into the body interior, indicating that the carcass dried out before burial. The specimen would thus constitute the fossil of a natural mummy. After dehydration, the mummy would have been rapidly buried by a meandering river, with bacteria consolidating the surrounding sediments, resulting in its excellent preservation.


Elasmaria is a clade of iguanodont ornithopods known from Cretaceous deposits in South America, Antarctica, and Australia.


Hadrosaurids (Greek: ἁδρός, hadrós, "stout, thick"), or duck-billed dinosaurs, are members of the ornithischian family Hadrosauridae. This group is known as the duck-billed dinosaurs for the flat duck-bill appearance of the bones in their snouts. The family, which includes ornithopods such as Edmontosaurus and Parasaurolophus, was a common group of herbivores during the Late Cretaceous Period in what is now Asia, Europe, Antarctica, South America, and North America. Hadrosaurids are descendants of the Upper Jurassic/Lower Cretaceous iguanodontian dinosaurs and had a similar body layout.

Like other ornithischians, hadrosaurids had a predentary bone and a pubic bone which was positioned backwards in the pelvis. Hadrosauridae is divided into two principal subfamilies: the lambeosaurines (Lambeosaurinae), which had hollow cranial crests or tubes; and the saurolophines (Saurolophinae), identified as hadrosaurines (Hadrosaurinae) in most pre-2010 works, which lacked hollow cranial crests (solid crests were present in some forms). Saurolophines tended to be bulkier than lambeosaurines. Lambeosaurines included the aralosaurins, tsintaosaurins, lambeosaurins and parasaurolophins, while saurolophines included the brachylophosaurins, kritosaurins, saurolophins and edmontosaurins.

Hadrosaurids were facultative bipeds, with the young of some species walking mostly on two legs and the adults walking mostly on four. Their jaws were evolved for grinding plants, with multiple rows of teeth replacing each other as the teeth wore down.


Iguanodontia (the iguanodonts) is a clade of herbivorous dinosaurs that lived from the Middle Jurassic to Late Cretaceous. Some members include Camptosaurus, Dryosaurus, Iguanodon, Tenontosaurus, and the hadrosaurids or "duck-billed dinosaurs". Iguanodontians were one of the first groups of dinosaurs to be found. They are among the best known of the dinosaurs, and were among the most diverse and widespread herbivorous dinosaur groups of the Cretaceous period.


Jaxartosaurus is a genus of hadrosaurid dinosaur similar to Corythosaurus which lived during the Late Cretaceous. Its fossils were found in Kazakhstan.


Koshisaurus is a monospecific genus of basal hadrosauroid from the Kitadani Formation in Japan. The discovery of the genus suggests that hadrosauroids had higher diversity along the eastern margin of Asia in the Early Cretaceous. "Koshi" means an old Japanese regional name including Fukui prefecture where fossils of the genus were discovered.


Lapampasaurus is an extinct genus of hadrosaurid known from the Late Cretaceous Allen Formation (late Campanian or early Maastrichtian stage) of La Pampa Province, Argentina. It contains a single species, Lapampasaurus cholinoi.The generic name refers to the Argentine province of La Pampa. The specific name honours the late collector José Cholino. The material includes cervical, dorsal, sacral and caudal vertebrae, the forelimb girdle, and the partial hindlimb.


Mandschurosaurus is a genus of hadrosaurs based on material from the Upper Cretaceous of China.


Penelopognathus ("wild duck jaw") is a genus of dinosaur which lived during the Early Cretaceous. It was an iguanodont ancestral to hadrosaurids. Fossils have been found in the Bayin-Gobi Formation in what is now China. The type species, Penelopognathus weishampeli, was described by Godefroit, Li, and Shang in 2005, based on fragmentary jaw fossils.


Plesiohadros is an extinct genus of hadrosauroid dinosaur. It is known from a partial skeleton including the skull collected at Alag Teg locality, from the Campanian Djadochta Formation of southern Mongolia. The type species is Plesiohadros djadokhtaensis.


Rhabdodontomorpha is a clade of basal iguanodont dinosaurs. This group was named in 2016 in the context of the description, based on Spanish findings, of an early member of the Rhabdodontidae. A cladistic analysis was conducted in which it was found that Muttaburrasaurus was the sister species of the Rhabdodontidae sensu Weishampel. Therefore, Paul-Emile Dieudonné, Thierry Tortosa, Fidel Torcida Fernández-Baldor, José Ignacio Canudo and Ignacio Díaz-Martínez defined Rhabdodontomorpha as a nodal clade: the group consisting of the last common ancestor of Rhabdodon priscus Matheron, 1869 and Muttaburrasaurus langdoni Bartholomai and Molnar, 1981; and all its descendants. Within the clade are included also Zalmoxes and Mochlodon.The group consists of small to large plant eaters from Europe and Gondwana. It must have split from other iguanodont groups during the Middle Jurassic.


Stephanosaurus is a dubious genus of hadrosaurid dinosaur with a complicated taxonomic history.

In 1902, Lawrence Lambe named a new set of hadrosaurid limb material and other bones (originally GSC 419) from Alberta as Trachodon marginatus. Paleontologists began finding better remains of hadrosaurids from the same rocks in the 1910s, in what is now known as the late Campanian-age (Upper Cretaceous) Dinosaur Park Formation.

Lambe assigned two new skulls to T. marginatus, and based on the new information, coined the genus Stephanosaurus for the species in 1914. Lambe retained the original species marginatus, so the type specimen of Stephanosaurus was the original, scrappy limb bones and crushed skull fragments, not the two new skulls.

However, the limb bones and skull fragments could not be reliably said to come from the same animal as the complete skulls, or differentiated from other hadrosaurs. Because there was very little to associate the complete skulls with the scrappy earlier marginatus material, in 1923 William Parks proposed a new genus and species for the skulls, with both generic and specific names honoring Lambe: Lambeosaurus lambei (type specimen NMC 2869, originally GSC 2869). Stephanosaurinae, a group which Lambe named in 1920, was also renamed Lambeosaurinae.


Thespesius (meaning "wondrous one") is a dubious genus of hadrosaurid dinosaur from the late Maastrichtian-age Upper Cretaceous Lance Formation of South Dakota.


Xuwulong is a genus of hadrosauroid dinosaur from the Early Cretaceous period. It lived during the early Cretaceous period (Aptian-Albian age) in what is now Yujingzi Basin in the Jiuquan area, Gansu Province of northwestern China. It is known from the holotype – GSGM F00001, an articulated specimen including a complete cranium, almost complete axial skeleton, and complete left pelvic girdle from Xinminpu Group. Xuwulong was named by You Hailu, Li Daqing and Liu Weichang in 2011 and the type species is Xuwulong yueluni.


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