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Claosaurus (/ˌklˈsɔːrəs/ KLAY-o-SAWR-əs; Greek κλάω, klao meaning 'broken' and σαῦρος, sauros meaning 'lizard'; "broken lizard", referring to the odd position of the fossils when discovered) is a genus of primitive hadrosaurian (early duck-billed dinosaur) that lived during the Late Cretaceous Period (Campanian).

Temporal range: Late Cretaceous, 87–82 Ma
Type specimen in the Peabody Museum, with restored skull[1]
Scientific classification e
Kingdom: Animalia
Phylum: Chordata
Clade: Dinosauria
Order: Ornithischia
Suborder: Ornithopoda
Clade: Hadrosauromorpha
Genus: Claosaurus
Marsh, 1890
Type species
Hadrosaurus agilis
Marsh, 1872

Traditionally classified as an early member of the family Hadrosauridae, a 2008 analysis found Claosaurus agilis to be outside of the clade containing Hadrosaurus and other hadrosaurids, making it the closest not-hadrosaurid relative of true hadrosaurids within the clade Hadrosauria.[2]


Claosaurus had a slender body and slim feet, with long legs, small arms, and a long, stiff tail. It probably grew to a length of about 3.5 meters (11.5 feet) and weighed roughly 475 kg.

It appears to have walked on its hind legs, dropping to all fours only to graze. Like other hadrosaurs, it was an herbivore.


A Cretoxyrhina and two Squalicorax circling around a dead Claosaurus in the Western Interior Seaway

Evidence of its existence was first found near the Smoky Hill River in Kansas, United States in the form of partial skull fragments and as an articulated postcranial skeleton. Originally named Hadrosaurus agilis (Marsh, 1872), it was placed in a new genus and renamed Claosaurus agilis in 1890 when major differences between this specimen and Hadrosaurus came to light.

In 1892, Marsh named a second species, C. annectens. This species later was reassigned to Anatosaurus and then Edmontosaurus, where it is currently.[3] G. R. Wieland named third species C. affinis in 1903, which he compared to C. annectens. C. affinis was founded on remains from the Pierre Shale of South Dakota, found in association with remains of the giant sea turtle Archelon. At some point after its description, the fragmentary remains were mixed up with the original remains of C. agilis, and a toe bone from C. agilis was accidentally thought to be the only part of the holotype remains that could be located. This was corrected by Joseph Gregory in 1948, who found three toe bones from the right foot of a large hadrosaur in the Yale collections that had comparable preservation to the Pierre Shale turtle remains and were associated with labels in Wieland's handwriting. Gregory found the toe bones to be very similar in size to the corresponding bones of Marsh's Claosaurus annectens, but did not reassign the species due to its much older age and fragmentary remains.[4] "C. affinis" was considered a dubious hadrosaur in the 2004 review by Jack Horner and colleagues. They reported its type material as lost, although they also reported these remains as only including a single toe bone, instead of the three toe bones of Gregory.[3]

Reports of gastroliths, or stomach stones, in Claosaurus are actually based on a probable double misidentification. First, the specimen is actually of Edmontosaurus annectens. Barnum Brown, who discovered the specimen in 1900, referred to it as Claosaurus, because E. annectens was thought to be a species of Claosaurus at the time. Additionally, it is more likely that the supposed gastroliths represent gravel washed in during burial.[5]

See alsoEdit


^ * This species is not accepted as representing Claosaurus in reviews of the genus, but has not been given its own genus and is unlikely to receive one.


  1. ^
  2. ^ Prieto-Márquez, A. (2011). "Revised diagnoses of Hadrosaurus foulkii Leidy, 1858 (the type genus and species of Hadrosauridae Cope, 1869) and Claosaurus agilis Marsh, 1872 (Dinosauria: Ornithopoda) from the Late Cretaceous of North America". Zootaxa. 2765: 61–68.
  3. ^ a b Horner, John R.; Weishampel, David B.; Forster, Catherine A (2004). "Hadrosauridae". In Weishampel, David B.; Dodson, Peter; Osmólska, Halszka (eds.). The Dinosauria (2nd ed.). Berkeley: University of California Press. pp. 438–463. ISBN 0-520-24209-2.
  4. ^ Gregory, Joseph T. (1948). "The type of Claosaurus (?) affinis Wieland". American Journal of Science. 246: 29–30. doi:10.2475/ajs.246.1.29.
  5. ^ Creisler, Benjamin S. (2007). "Deciphering duckbills: a history in nomenclature". In Carpenter, Kenneth (ed.). Horns and Beaks: Ceratopsian and Ornithopod Dinosaurs. Bloomington and Indianapolis: Indiana University Press. pp. 185–210. ISBN 0-253-34817-X.