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   » » Wiki: Laosaurus
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Laosaurus (meaning "stone or lizard") is a of . The type species, Laosaurus celer, was first described by O.C. Marsh in 1878 from remains from the --age Morrison Formation of . 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 Allison Formation of , , Laosaurus minimus, are also considered .


History and taxonomy
Marsh (1878a) named his new genus from (YPM 1874) found by Samuel Wendell Williston at , , from rocks of the Morrison Formation. The material includes nine partial and two complete tail vertebral centra, which he concluded came from a "-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 ; and L. altus, originally based on a , hindlimb, and tooth (YPM 1876). A review by 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 ( ), 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 (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 (now ) and the skeleton to 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 () Allison Formation of , . At the time, though, the discovery locality was thought to be in the , but fieldwork at the L. minimus type locality in the early 1930s showed it to be within the Belly River Group, and 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 , from the Early Cretaceous of southern .

The next major publications which mentioned Laosaurus prominently were by Galton. In 1977, he assigned L. consors and L. gracilis to his new ; 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 " as " of the early 1980s, because it assigns L. minimus to Troodon, based on unpublished evidence. This would tie in with the / egg confusion of a few years later, which was eventually settled as Troodon individuals eating Orodromeus individuals at their nesting site (the were confused with hypsilophodont embryoes). L. celer was assessed as dubious by Galton, a status it has kept through the last major reviews.

(1990). 9780520067271, University of California Press.
(2025). 9780520242098, University of California Press.

Two further developments have occurred. First, L. minimus is seen as a possible second species or specimen of (Sues and Norman, 1990), although the remains are too meager to be certain. Second, Galton, in a 2007 review, declared to be based on undiagnostic remains, and shifted diagnostic referred remains to new taxon , a new combination based on the original L. consors partial skeleton.

(2025). 9780253348173, Indiana University Press.


Taxonomic summary


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