Coloradisaurus (meaning "Colorados [from Los Colorados Formation] lizard") is a genus of massospondylid sauropodomorph dinosaur. It lived during the Late Triassic period (Norian to Rhaetian stages) in what is now La Rioja Province, Argentina. It is known from the holotype PVL 5904, a nearly complete skull. It was discovered and collected from the upper section of the Los Colorados Formation of the Ischigualasto-Villa UniĆ³n Basin.
Taxonomy[]
Originally named Coloradia by Jose F. Bonaparte in 1978,[1] this name had already been assigned to a moth, and so the animal was renamed. The genus was first named by David Lambert in 1983 and the type species is Coloradisaurus brevis.[2] It may in fact be an adult specimen of Mussaurus. Cladistic analyses by Yates (2007), Yates et al. (2010, 2011) and Novas et al. (2011) found that Coloradisaurus is basal to the Glacialisaurus-Lufengosaurus clade within Massospondylidae.[3][4]
Description[]
The holotype of Coloradisaurus (PVL 3967) is a mostly complete skull found associated with an undescribed partial skeleton. While the right side of the skull is well-preserved with almost all bones intact, the left side is distorted and missing more bones. The holotype individual has been estimated to have been 3 m (10 ft) long with a mass of 70 kg (150 lb). 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. 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. The top of the Los Colorados Formation has been dated to 213 Ma, which would place Coloradisaurus in the Norian stage of the Late Triassic.
Phylogeny[]
Coloradisaurus was classified as a plateosaurid in the original description by Bonaparte, but this pre-dated the use of phylogenetic analyses in paleontology. He later became opposed to cladistics and continued to consider Coloradisaurus a plateosaurid without testing its phylogenetic position. The analyses of Galton (1990), Galton & Upchurch (2004), and Upchurch et al. (2007) found it to be a plateosaurid, supporting Bonaparte's placement. 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. Subsequent analyses such as Yates et al. (2010), Apaldetti et al. (2013; 2014), Wang et al. (2017), and MĆ¼ller (2020) have reached the consensus that Coloradisaurus is a massospondylid most closely related to Lufengosaurus and Glacialisaurus. These three taxa share four synapomorphies found in the metatarsals and femur.
Below is a simplified cladogram after Galton & Upchurch (2004), reflecting its early placement as a plateosaurid.
| Sauropodomorpha |
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Below is a simplified cladogram after MĆ¼ller (2020), showing its current position as a massospondylid.
| Plateosauria |
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