Laosaurus

Taxobox
name = "Laosaurus"
fossil_range = Upper Jurassic, Upper Cretaceous
regnum = Animalia
phylum = Chordata
classis = Sauropsida
superordo = Dinosauria
ordo = Ornithischia
subordo = Cerapoda
infraordo = Ornithopoda
familia = Hypsilophodontidae
genus = "Laosaurus"
genus_authority = Marsh, 1878
subdivision_ranks = Species
subdivision =
* "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.

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.cite journal |last=Marsh |first=Othniel Charles |authorlink=Othniel Charles Marsh |year=1878 |title=Notice of new dinosaurian reptiles |journal=American Journal of Science and Arts |volume=15 |pages=241–244] 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;cite journal |last=White |first=T.E. |year=1973 |title=Catalogue of the genera of dinosaurs |journal=Annals of Carnegie Museum |volume=44 |pages=117–155] and "L. altus", originally based on a pelvis, hindlimb, and tooth (YPM 1876).cite journal |last=Marsh |first=Othniel Charles |year=1878 |title=Principal characters of American Jurassic dinosaurs. Part I |journal=American Journal of Science and Arts |volume=16 |pages=411–416] 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.cite journal |last=Galton |first=Peter M. |authorlink=Peter Galton |year=1983 |title=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 |journal=Geologica et Palaeontologica |volume=17 |pages=207–243] Charles Gilmore had assigned additional remains, including a partial skeleton (CM 11340), to "L. gracilis" based on size,cite journal |last=Gilmore |first=Charles W. |authorlink=Charles W. Gilmore |year=1909 |title=A new rhynchocephalian reptile from the Jurassic of Wyoming, with notes on the fauna of "Quarry 9" |journal=Proceedings of the U.S. National Museum |volume=37 |pages=35–42] cite journal |last=Gilmore |first=Charles W. |year=1925 |title=Osteology of ornithopodous dinosaurs from the Dinosaur National Monument, Utah |journal=Memoir of the Carnegie Museum |volume=10 |pages=385–409] but Galton transferred the remains to other taxa, assigning the skeleton to "Dryosaurus".

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.cite journal |last=Marsh |first=Othniel Charles |year=1894 |title=The typical Ornithopoda of the American Jurassic |journal=American Journal of Science (Series 3) |volume=48 |pages=85–90] In 1895, he coined the family Laosauridae for his genus, but this was eventually considered synonymous with Hypsilophodontidae.cite journal |last=Marsh |first=Othniel Charles |year=1895 |title=On the affinities and classification of the dinosaurian reptiles |journal=American Journal of Science |volume=50 |issue=300 |pages=483–498]

Charles Gilmore in 1909 assigned a juvenile femur (USNM 5808) to "L. gracilis",cite journal |last=Gilmore |first=Charles W. |authorlink=Charles W. Gilmore |year=1909 |title=A new rhynchocephalian reptile from the Jurassic of Wyoming, with notes on the fauna of "Quarry 9" |journal=Proceedings of the U.S. National Museum |volume=37 |pages=35–42] and in 1925 added partial skeleton (CM 11340) to "L. gracilis", based on size,cite journal |last=Gilmore |first=Charles W. |year=1925 |title=Osteology of ornithopodous dinosaurs from the Dinosaur National Monument, Utah |journal=Memoir of the Carnegie Museum |volume=10 |pages=385–409] 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.cite journal |last=Gilmore |first=Charles W. |year=1924 |title=A new species of "Laosaurus", an ornithischian dinosaur from the Cretaceous of Alberta |journal=Transactions of the Royal Society of Canada, section 4, series 3 |volume=18 |pages=1–6] 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".cite journal |last=Russell |first=Loris S. |year=1949 |title=The relationships of the Alberta Cretaceous dinosaur "Laosaurus" "minimus" Gilmore |journal=Journal of Paleontology |volume=23 |issue=5 |pages=518–520] 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.

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";cite journal |last=Galton |first=Peter M. |year=1977 |title=The ornithopod dinosaur "Dryosaurus" and a Laurasia-Gondwanaland connection in the Upper Jurassic |journal=Nature |volume=268 |pages=230–232 |doi=10.1038/268230a0] and in 1983 he redescribed most of the material and reassigned some of it, as described above. 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. 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).cite journal |last=Varricchio |first=D.J.; Jackson, F.; Borkowski, J.J.; and Horner, J.R. |year=1997 |title=Nest and egg clutches of the dinosaur "Troodon formosus" and the evolution of the avian reproductive system |journal=Nature |volume=385 |pages=247–250 |doi=10.1038/385247a0] "L. celer" was assessed as dubious by Galton, a status it has kept through the last major revisions.cite book |last=Sues |first=Hans-Dieter |coauthors=and Norman, David B. |editor= Weishampel, David B.; Dodson, Peter; and Osmólska, Halszka (eds.)|title=The Dinosauria |edition=1st |year=1990 |publisher=University of California Press |location=Berkeley |isbn=0-520-06727-4 |pages=498–509 |chapter=Hypsilophodontidae, "Tenontosaurus", Dryosauridae] cite book |last=Norman |first=David B. |authorlink=David B. Norman |coauthors=Sues, Hans-Dieter; Witmer, Larry M.; and Coria, Rodolfo A. |editor=Weishampel, David B.; Dodson, Peter; and Osmólska, Halszka (eds.)|title=The Dinosauria |edition=2nd |year= 2004|publisher=University of California Press |location=Berkeley |isbn=0-520-24209-2 |pages=393–412 |chapter=Basal Ornithopoda]

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. Second, Galton, in a 2007 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.cite book |last=Galton |first=Peter M. |year=2007 |chapter=Teeth of ornithischian dinosaurs (mostly Ornithopoda) from the Morrison Formation (Upper Jurassic) of the western United States |editor=Carpenter, K. (ed.) |title=Horns and Beaks: Ceratopsian and Ornithopod Dinosaurs |publisher=Indiana University Press |location=Bloomington and Indianapolis |pages=17-47 |isbn=0-253-34817-X]

Taxonomic summary

*"L. celer" (type species) = dubious basal ornithopod
*"L. altus" = "Dryosaurus altus"
*"L. consors" = "Othnielosaurus consors"
*"L. gracilis" = unknown ("gracilis" predates "consors", which would require a name change if referred to "Othnielosaurus consors"), probably a dubious basal ornithopod
*"L. minimus" = dubious basal ornithopod, possibly the same as "Orodromeus"

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.

References

External links

* [http://dml.cmnh.org/1995Aug/msg00194.html More on the taxonomy of "Nanosaurus", "Othnielia", and "Laosaurus"] , from the Dinosaur Mailing List
* [http://links.jstor.org/sici?sici=0022-3360%28194909%2923%3A5%3C518%3ATROTAC%3E2.0.CO%3B2-F&size=LARGE First page and abstract of Russell, 1949]