Laosaurus

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Laosaurus
Fossil range: Upper Jurassic, Upper Cretaceous
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Sauropsida
Superorder: Dinosauria
Order: Ornithischia
Suborder: Cerapoda
Infraorder: Ornithopoda
Family: Hypsilophodontidae
Genus: Laosaurus
Marsh, 1878
Species
  • L. celer Marsh, 1878 (type) (nomen dubium)
  • L. gracilis Marsh, 1878 (nomen dubium)
  • L. minimus Gilmore, 1909 (nomen dubium)

Laosaurus (meaning "stone or fossil lizard") is a genus of hypsilophodont dinosaur. The type species is Laosaurus celer, first described by O.C. Marsh in 1878 from remains from the Oxfordian-Tithonian-age Upper Jurassic Morrison Formation of Wyoming. The validity of this genus is doubtful because it is based on fragmentary fossils. A second species from the Morrison Formation, L. gracilis, and a species from the late Cretaceous of Alberta, Laosaurus minimus, are also considered dubious. It is believed that the three species were hypsilophodonts, basal ornithopods.

Contents

[edit] History and taxonomy

Marsh (1878a) named his new genus from vertebrae (YPM 1874) found by Samuel Wendell Williston at Como Bluff, Wyoming, from rocks of the Morrison Formation. The type material includes nine partial and two complete tail vertebral centra, which he concluded came from a "fox-sized" animal.[1] In the same year, he named two other species: L. gracilis, originally based on a back vertebral centrum, a tail vertebral centrum, and part of an ulna;[1][2] and L. altus, originally based on a pelvis, hindlimb, and tooth (YPM 1876).[3] A review by Peter Galton in 1983 found the type of L. gracilis to consist of thirteen back and eight tail centra, and portions of both hindlimbs.[4] Charles Gilmore had assigned additional remains, including a partial skeleton (CM 11340), to L. gracilis based on size,[5][6] but Galton transferred the remains to other taxa, assigning the skeleton to Dryosaurus.[4]

Othniel Charles Marsh's 1896 skeletal restoration of "Laosaurus" consors (now Othnielosaurus).
Othniel Charles Marsh's 1896 skeletal restoration of "Laosaurus" consors (now Othnielosaurus).

Marsh returned to the genus in 1894, when additional remains convinced him that L. altus deserved its own genus (Dryosaurus), and that there was another species present: L. consors, based on YPM 1882, a partial skeleton also from Como Bluff.[7] In 1895, he coined the family Laosauridae for his genus, but this was eventually considered synonymous with Hypsilophodontidae.[8]

Charles Gilmore in 1909 assigned a juvenile femur (USNM 5808) to L. gracilis,[5] and in 1925 added partial skeleton (CM 11340) to L. gracilis, based on size,[6] but Galton transferred the femur to Othnielia and the skeleton to Dryosaurus in 1983. Gilmore also described the fifth and final species, L. minimus (species name for its small size), based on NMC 9438, a partial left hindlimb and vertebral bits from the Oldman Formation (Upper Cretaceous, late Campanian-age) of Alberta, Canada.[9] At the time, though, the discovery locality was thought to be in the Lower Cretaceous Blairmore Formation, which may partially explain why Gilmore chose to assign the remains to the late Jurassic genus Laosaurus.[10] Loris Russell in 1949 pointed out the new geological information and disputed the generic assignment, recommending that it be referred to as "Laosaurus" minimus. He found it to be most like Hypsilophodon, from the Lower Cretaceous Wealden of England.[10]

The next major publications which mentioned Laosaurus prominently were by Galton. In 1977, he assigned L. consors and L. gracilis to his new taxon Othnielia rex;[11] and in 1983 he redescribed most of the material and reassigned some of it, as described above.[4] Galton (1983) is also one of the sources for the "Troodon as carnivorous ornithopod" hypothesis of the early 1980s, because it assigns L. minimus to Troodon based on unpublished evidence.[4] This would tie in with the Orodromeus/Troodon egg confusion of a few years later, which was eventually settled as Troodon individuals eating Orodromeus individuals at their nesting site (the troodontid embryoes were confused with hypsilophodont embryoes).[12] L. celer was assessed as dubious by Galton, a status it has kept through the last major revisions.[13][14]

Two further developments have occurred. First, L. minimus is seen as a possible second species or specimen of Orodromeus (Sues and Norman, 1990), although the remains are too meager to be certain.[13] Second, Galton, in a 2006 review, declared Othnielia rex to be based on undiagnostic remains, and shifted diagnostic referred remains to new taxon Othnielosaurus consors, a new combination based on the original L. consors partial skeleton.[15]

[edit] Taxonomic summary

  • L. celer (type species) = dubious basal ornithopod[14]
  • L. altus = Dryosaurus altus[7]
  • L. consors = Othnielosaurus consors[15]
  • L. gracilis = unknown (gracilis predates consors, which would require a name change if referred to Othnielosaurus consors), probably a dubious basal ornithopod[14]
  • L. minimus = dubious basal ornithopod, possibly the same as Orodromeus[13]

[edit] Paleobiology

Too little of the various species is known to make any detailed assessments, but as hypsilophodonts or basal ornithopods, they were probably small, bipedal cursorial herbivores.[14]

[edit] References

  1. ^ a b Marsh, Othniel Charles (1878). "Notice of new dinosaurian reptiles". American Journal of Science and Arts 15: 241–244. 
  2. ^ White, T.E. (1973). "Catalogue of the genera of dinosaurs". Annals of Carnegie Museum 44: 117–155. 
  3. ^ Marsh, Othniel Charles (1878). "Principal characters of American Jurassic dinosaurs. Part I". American Journal of Science and Arts 16: 411–416. 
  4. ^ a b c d Galton, Peter M. (1983). "The cranial anatomy of Dryosaurus, a hypsilophodontid dinosaur from the Upper Jurassic of North America and East Africa, with a review of hypsilophodontids from the Upper Jurassic of North America". Geologica et Palaeontologica 17: 207–243. 
  5. ^ a b Gilmore, Charles W. (1909). "A new rhynchocephalian reptile from the Jurassic of Wyoming, with notes on the fauna of "Quarry 9"". Proceedings of the U.S. National Museum 37: 35–42. 
  6. ^ a b Gilmore, Charles W. (1925). "Osteology of ornithopodous dinosaurs from the Dinosaur National Monument, Utah". Memoir of the Carnegie Museum 10: 385–409. 
  7. ^ a b Marsh, Othniel Charles (1894). "The typical Ornithopoda of the American Jurassic". American Journal of Science (Series 3) 48: 85–90. 
  8. ^ Marsh, Othniel Charles (1895). "On the affinities and classification of the dinosaurian reptiles". American Journal of Science 50 (300): 483–498. 
  9. ^ Gilmore, Charles W. (1924). "A new species of Laosaurus, an ornithischian dinosaur from the Cretaceous of Alberta". Transactions of the Royal Society of Canada, section 4, series 3 18: 1–6. 
  10. ^ a b Russell, Loris S. (1949). "The relationships of the Alberta Cretaceous dinosaur "Laosaurus" minimus Gilmore". Journal of Paleontology 23 (5): 518–520. 
  11. ^ Galton, Peter M. (1977). "The ornithopod dinosaur Dryosaurus and a Laurasia-Gondwanaland connection in the Upper Jurassic". Nature 268: 230–232. 
  12. ^ Varricchio, D.J.; Jackson, F.; Borkowski, J.J.; and Horner, J.R. (1997). "Nest and egg clutches of the dinosaur Troodon formosus and the evolution of the avian reproductive system". Nature 385: 247–250. 
  13. ^ a b c Sues, Hans-Dieter; and Norman, David B. (1990). "Hypsilophodontidae, Tenontosaurus, Dryosauridae", in Weishampel, David B.; Dodson, Peter; and Osmólska, Halszka (eds.): The Dinosauria, 1st, Berkeley: University of California Press, 498–509. ISBN 0-520-06727-4. 
  14. ^ a b c d Norman, David B.; Sues, Hans-Dieter; Witmer, Larry M.; and Coria, Rodolfo A. (2004). "Basal Ornithopoda", in Weishampel, David B.; Dodson, Peter; and Osmólska, Halszka (eds.): The Dinosauria, 2nd, Berkeley: University of California Press, 393–412. ISBN 0-520-24209-2. 
  15. ^ a b Galton, Peter M. (2006). "Teeth of ornithischian dinosaurs (mostly Ornithopoda) from the Morrison Formation (Upper Jurassic) of the western United States", in Carpenter, K. (ed.): Horns and Beaks: Ceratopsian and Ornithopod Dinosaurs. Bloomington and Indianapolis: Indiana University Press, 17-47. ISBN 0-253-34817-X. 

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