Coloradisaurus

Coloradisaurus was originally named Coloradia brevis by José Bonaparte in 1978,[4] but that genus name was preoccupied by the pine moth Coloradia.[5] David Lambert unintentionally proposed Coloradisaurus as a replacement name in 1983.[6] Lambert had gotten the name from Bonaparte in a personal communication and mistakenly thought that Bonaparte had already published it.[3] Since it was not stated to be a new name, and it did not have a diagnosis or type species, it was a nomen nudum.[3] In 1990, Peter Galton provided both a diagnosis and a type species for Coloradisaurus while still crediting the name to Lambert.[2] Although similarly unintentional, Galton's description meets the requirements of the ICZN and the authorship of Coloradisaurus should be attributed to him.[3]

The holotype of Coloradisaurus (PVL 3967) is a mostly complete skull found associated with an undescribed partial skeleton.[4] While the right side of the skull is well-preserved with almost all bones intact, the left side is distorted and missing more bones.[7] The holotype individual has been estimated to have been 3 m (10 ft) long with a mass of 70 kg (150 lb).[8] A referred specimen (PVL 5904) is a partial skeleton including the most of the dorsal vertebrae and parts of the pectoral and pelvic girdles and limbs.[9] All of this material was discovered in 1971 at the La Esquina locality in the upper section of the Los Colorados Formation near Pagancillo, La Rioja Province, Argentina.[4][7][9] The top of the Los Colorados Formation has been dated to 213 Ma,[1] which would place Coloradisaurus in the Norian stage of the Late Triassic.

Coloradisaurus was classified as a plateosaurid in the original description by Bonaparte,[4] but this pre-dated the use of phylogenetic analyses in paleontology. He later became opposed to cladistics[10] and continued to consider Coloradisaurus a plateosaurid without testing its phylogenetic position.[11] The analyses of Galton (1990), Galton & Upchurch (2004), and Upchurch et al. (2007) found it to be a plateosaurid, supporting Bonaparte's placement.[2][12][13] However, the analyses of Benton et al. (2000) and Yates (2003) recovered it in a polytomy with other basal sauropodomorphs or as a massospondylid, respectively.[14][15] Subsequent analyses such as Yates et al. (2010), Apaldetti et al. (2013; 2014), Wang et al. (2017), and Müller (2020) have reached the consensus that Coloradisaurus is a massospondylid most closely related to Lufengosaurus and Glacialisaurus.[7][9][16][17][18] These three taxa share four synapomorphies found in the metatarsals and femur.[9]

Below is a simplified cladogram after Galton & Upchurch (2004), reflecting its early placement as a plateosaurid.[12]

Below is a simplified cladogram after Müller (2020), showing its current position as a massospondylid.[18]