Coloradisaurus

Coloradisaurus Temporal range: Norian ~213 Ma PreꞒ Ꞓ O S D C P T J K Pg N ↓ [1]
Diagram showing known skull elements; shaded parts represent missing bones
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Clade:	Dinosauria
Clade:	Saurischia
Clade:	†Sauropodomorpha
Family:	†Massospondylidae
Genus:	†Coloradisaurus Galton, 1990[2][3]
Type species
†Coloradisaurus brevis (Bonaparte, 1978)[4]
Synonyms
Coloradia brevis Bonaparte, 1978 (preoccupied by Coloradia Blake, 1863)[5] "Coloradisaurus" Lambert, 1983 (nomen nudum)[3][6]

Coloradisaurus (meaning "Los Colorados lizard") is a genus of massospondylid sauropodomorph dinosaur. It lived during the Late Triassic period (Norian stage) in what is now La Rioja Province, Argentina. It is known from two specimens collected from the Los Colorados Formation of the Ischigualasto-Villa Unión Basin.

Taxonomy[]

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]

Description[]

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.

Phylogeny[]

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]

References[]