Laosaurus

''Laosaurus'' (meaning "stone or fossil lizard") is a genus of neornithischian dinosaur. The type species, ''Laosaurus celer'', was 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 Allison Formation of Alberta, Canada, ''Laosaurus minimus'', are also considered dubious.

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. 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; and ''L. altus'', originally based on a pelvis, hindlimb, and tooth (YPM 1876). 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. Charles Gilmore had assigned additional remains, including a partial skeleton ( CM 11340), to ''L. gracilis'' based on size, 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. In 1895, he coined the family Laosauridae for his genus, but this was eventually considered synonymous with Hypsilophodontidae.

Charles Gilmore in 1909 assigned a juvenile femur (USNM 5808) to ''L. gracilis'', and in 1925 added partial skeleton CM 11340 to ''L. gracilis'', based on size, but Galton transferred the femur to ''Othnielia'' (now ''Nanosaurus'') 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 Late Cretaceous (late Campanian) Allison Formation of Alberta, Canada. At the time, though, the discovery locality was thought to be in the Early Cretaceous Blairmore Group, but fieldwork at the ''L. minimus'' type locality in the early 1930s showed it to be within the Belly River Group, and Loris Russell published a paper in 1949 recognizing this new geologic information, while finding it generically distinct from ''Laosaurus'' proper. Russell found this taxon to be most like ''Hypsilophodon'', from the Early Cretaceous Wessex Formation of southern 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''; 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). ''L. celer'' was assessed as dubious by Galton, a status it has kept through the last major reviews.

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.

Taxonomic summary

*''L. celer'' (type species) = dubious ornithischian
*''L. altus'' = ''Dryosaurus altus''
*''L. consors'' = '' Othnielosaurus consors'', now considered a junior synonym of '' Nanosaurus agilis''
*''L. gracilis'' = dubious ornithishian
*''L. minimus'' = dubious ornithischian, possibly orodromine

References

External links

More on the taxonomy of ''Nanosaurus'', ''Othnielia'', and ''Laosaurus''
from the Dinosaur Mailing List
First page and abstract of Russell, 1949

{{Taxonbar, from=Q1657525

Nomina dubia
Late Jurassic dinosaurs of North America
Dinosaurs of the Morrison Formation
Taxa named by Othniel Charles Marsh
Fossil taxa described in 1878
Paleontology in Wyoming
Ornithischian genera