Los Colorados Formation

Los Colorados Formation
Los Colorados Formation
Stratigraphic range: Norian; ~227–213 Ma PreꞒ Ꞓ O S D C P T J K Pg N I O An. La. Carn. Norian Rh.
	Los Colorados massif, La Rioja Province, Argentina
Type	Geological formation
Unit of	Agua de la Peña Group
Underlies	Cerro Rajado Formation
Overlies	Ischigualasto Formation
Thickness	600 m (2,000 ft)
Lithology
Primary	Sandstone, siltstone, mudstone
Other	Conglomerate, gypsum
Location
Coordinates	29°48′S 67°54′W / 29.8°S 67.9°W
Approximate paleocoordinates	38°54′S 31°24′W / 38.9°S 31.4°W
Region	San Juan Province; La Rioja Province
Country	Argentina
Extent	Ischigualasto-Villa Unión Basin
Type section
Named for	Los Colorados Massif
	Los Colorados Formation (Argentina)

The Los Colorados Formation is a sedimentary rock formation of the Ischigualasto-Villa Unión Basin, found in the provinces of San Juan and La Rioja in Argentina. The formation dates back to the Norian age of the Late Triassic.

The up to 600 metres (2,000 ft) thick formation comprises sandstones, siltstones, mudstones and conglomerates with gypsum layers deposited in a fluvial to lacustrine environment. The formation is the uppermost stratigraphic unit of the Agua de la Peña Group, overlying the Lagerstätte of the Ischigualasto Formation. Los Colorados Formation is partly covered by the Cretaceous Cerro Rajado Formation, separated by an unconformity.

The formation is known for its fossils of early dinosaurs, including the coelophysoid Zupaysaurus and the "prosauropods" Coloradisaurus, Lessemsaurus, and Riojasaurus. Magnetostratigraphic analysis suggests that the Los Colorados Formation was deposited between 227 and 213 million years ago.

Description

Los Colorados Formation is a unit with an approximate thickness of 600 metres (2,000 ft) of the Agua de la Peña Group in the Ischigualasto-Villa Unión Basin, where it is exposed in the Ischigualasto Provincial Park, a World Heritage Site in Argentina. The formation gradually overlies the Ischigualasto Formation and is unconformably overlain by the Cretaceous Cerro Rajado Formation. The formation comprises red-colored, fine- to medium-grain–size sandstones together with siltstones and ancillary floodplain mudstones with early calcisol development. The formation was deposited in a fluvial to lacustrine environment.

Fossil content

Synapsids

Synapsids of Los Colorados Formation
Genus	Species	Location	Material	Notes	Images
Chaliminia	C. musteloides			A tritheledontid cynodont.
Jachaleria	J. colorata		A skull and complete jaws.	A large stahleckeriid dicynodont, also found in the uppermost layers of the Ischigualasto Formation.
Tessellatia	T. bonapartei		A partial skull, including the snout, orbital region, and lower jaws.	A probainognathian cynodont.

Archosauromorphs

Non-crocodylomorph pseudosuchians

Non-crocodylomorph pseudosuchians of Los Colorados Formation
Genus	Species	Location	Material	Notes	Images
Fasolasuchus	F. tenax	La Rioja Province	A fragmented skull and jaws.	A large predatory loricatan (traditionally known as a "rauisuchian").
Neoaetosauroides	N. engaeus	Quebrada de los Jachaleros, El Salto (San Juan)		An early desmatosuchine aetosaur with adaptations for a diet of small animals.
Olkasuchus	O. walasto		An incomplete axial skeleton, partial pectoral and pelvic girdles, partial forelimb and hindlimb, and both articulated and isolated osteoderms.	An early desmatosuchine aetosaur
Riojasuchus	R. tenuisceps		Four specimens, including two nearly complete skeletons	An ornithosuchid, one of the last and most complete members of its family.

Crocodylomorpha

Crocodylomorphs of the Los Colorados Formation
Genus	Species	Location	Material	Notes	Images
Coloradisuchus	C. abelini	La Rioja Province		A protosuchid
Hemiprotosuchus	H. leali	Quebrada de los Jachaleros, El Salto (San Juan)		A protosuchid
Pseudhesperosuchus	P. jachaleri	Quebrada de los Jachaleros, El Salto (San Juan)		A "sphenosuchian" (slender early crocodylomorph)

Dinosaurs

Indeterminate theropod remains present in the Provincia de la Rioja.

Dinosaurs of the Los Colorados Formation
Genus	Species	Location	Material	Notes	Images
Coloradisaurus	C. brevis	La Rioja Province	Skull, adult	A massospondylid sauropodomorph
Lessemsaurus	L. sauropoides	La Rioja Province	Partial cervical, dorsal, and sacral vertebrae, adult	A lessemsaurid sauropodiform
Prosauropoda	Indeterminate	La Rioja & San Juan Provinces	Includes Strenusaurus procerus. Dorsals, caudals, partial fore- and hindlimb.	Indeterminate fossils of "prosauropods" (early sauropodomorphs)
Powellvenator	P. podocitus	Ischigualasto-Villa Unión Basin	Known from previously undescribed partial hindlimbs	A coelophysoid theropod
Riojasaurus	R. incertus	La Rioja Province		A sauropodomorph
Zupaysaurus	Z. rougieri	La Rioja Province		An early theropod

Other reptiles

Other reptiles of Los Colorados Formation
Genus	Species	Location	Material	Notes	Images
Coloradosphenodon	C. lahni	La Esquina locality, La Rioja Province	A partial skull	An early rhynchocephalian
Palaeochersis	P. talampayensis			A testudinatan (early turtle) in the family Australochelyidae.

Ichnofossils

References

1 2 3 4 5 6 7 8 Weishampel et al., 2004, pp.527-528
1 2 Kent et al, 2014, p.7959
1 2 3 4 5 6 7 8 9 10 Arcucci et al., 2004, p.561
↑ Gaetano, L. C.; Abdala, F.; Seoane, F. D.; Tartaglione, A.; Schulz, M.; Otero, A.; Leardi, J. M.; Apaldetti, C.; Krapovickas, V.; Steimbach, E. (2022). "A new cynodont from the Upper Triassic Los Colorados Formation (Argentina, South America) reveals a novel paleobiogeographic context for mammalian ancestors". Scientific Reports. 12 (1) 6451. Bibcode:2022NatSR..12.6451G. doi:10.1038/s41598-022-10486-4. PMC 9038739. PMID 35468982.
↑ Sotomayor, Juan C.; Leardi, Juan Martín; Desojo, Julia Brenda; Gaetano, Leandro Carlos; Otero, Alejandro; Apaldetti, Cecilia. "Olkasuchus walasto, a new taxon of Aetosauria (Archosauria; Pseudosuchia) from the Los Colorados Formation (Upper Triassic), Argentina". Historical Biology. 0 (0): 1–22. doi:10.1080/08912963.2025.2571751. hdl:11336/280616. ISSN 0891-2963.
↑ Von Baczko & Desojo, 2016, p.4
1 2 Martínez et al., 2018, p.1
1 2 "Table 12.1," in Weishampel et al., 2004. p.234
↑ "Table 12.1," in Weishampel, et al., 2004. Page 237.
↑ Ezcurra, 2017
↑ Gaetano, Leandro C.; Sotomayor Chacón, Juan C.; Arcaria, María R.; Vega, Nahuel; Leardi, Juan M.; Seoane, Federico D.; Otero, Alejandro (2026-09-05). "Earliest-diverging rhynchocephalian from Gondwana: a new sphenodontian from the Upper Triassic Los Colorados Formation (northwestern Argentina)". Scientific Reports. doi:10.1038/s41598-026-68493-8. ISSN 2045-2322.
↑ 2 km NE of La Esquina at Fossilworks.org
↑ Río de los Tarros tracksite at Fossilworks.org
↑ Leonardi, 1994, p.25
↑ Leonardi locality 15 at Fossilworks.org

Bibliography

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Von Baczko, Maria Belén; Desojo, Julia Brenda (2016), "Cranial Anatomy and Palaeoneurology of the Archosaur Riojasuchus tenuisceps from the Los Colorados Formation, La Rioja, Argentina", PLoS ONE, 11 (2): 1–30, Bibcode:2016PLoSO..1148575V, doi:10.1371/journal.pone.0148575, PMC 4743959, PMID 26849433
Ezcurra, Martín D (2017), "A new early coelophysoid neotheropod from the Late Triassic of northwestern Argentina", Ameghiniana, 54 (5): Abstract, doi:10.5710/AMGH.04.08.2017.3100, hdl:11336/56719, retrieved 2019-03-26
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Leonardi, Giuseppe (1994), Annotated Atlas of South America Tetrapod Footprints (Devonian to Holocene) with an appendix on Mexico and Central America, Ministerio de Minas e Energia - Companhia de Pesquisa de Recursos Minerais, Geological Service of Brazil, pp. 1–248, retrieved 2019-03-25
Martínez, Ricardo N.; Alcober, Oscar A.; Pol, Diego (2018), "A new protosuchid crocodyliform (Pseudosuchia, Crocodylomorpha) from the Norian Los Colorados Formation, northwestern Argentina", Journal of Vertebrate Paleontology, 38 (4): 1–12, doi:10.1080/02724634.2018.1491047, hdl:11336/98862, retrieved 2019-03-28
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J. F. Bonaparte and J. A. Pumares. 1995. Notas sobre el primer craneo de Riojasaurus incertus (Dinosauria, Prosauropoda, Melanorosauridae) del Triasico Superior de La Rioja, Argentina [Notes on the first skull and jaws of Riojasaurus incertus (Dinosauria, Prosauropoda, Melanorosauridae), Late Triassic of La Rioja, Argentina]. Ameghiniana 32(4):341-349
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M. D. Ezcurra and C. Apaldetti. 2012. A robust sauropodomorph specimen from the Upper Triassic of Argentina and insights on the diversity of the Los Colorados Formation. Proceedings of the Geologists' Association 123:155-164
A. G. Martinelli and G. W. Rougier. 2007. On Chaliminia musteloides (Eucynodontia: Tritheledontidae) from the Late Triassic of Argentina, and a phylogeny of Ictidosauria. Journal of Vertebrate Paleontology 27:442-460
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[triassicdistribution-1] 1 2 3 4 5 6 7 8 Weishampel et al., 2004, pp.527-528

[Kent2014_p7959-2] 1 2 Kent et al, 2014, p.7959

[Arcucci2004_p561-3] 1 2 3 4 5 6 7 8 9 10 Arcucci et al., 2004, p.561

[4] Gaetano, L. C.; Abdala, F.; Seoane, F. D.; Tartaglione, A.; Schulz, M.; Otero, A.; Leardi, J. M.; Apaldetti, C.; Krapovickas, V.; Steimbach, E. (2022). "A new cynodont from the Upper Triassic Los Colorados Formation (Argentina, South America) reveals a novel paleobiogeographic context for mammalian ancestors". Scientific Reports. 12 (1) 6451. Bibcode:2022NatSR..12.6451G. doi:10.1038/s41598-022-10486-4. PMC 9038739. PMID 35468982.

[5] Sotomayor, Juan C.; Leardi, Juan Martín; Desojo, Julia Brenda; Gaetano, Leandro Carlos; Otero, Alejandro; Apaldetti, Cecilia. "Olkasuchus walasto, a new taxon of Aetosauria (Archosauria; Pseudosuchia) from the Los Colorados Formation (Upper Triassic), Argentina". Historical Biology. 0 (0): 1–22. doi:10.1080/08912963.2025.2571751. hdl:11336/280616. ISSN 0891-2963.

[VonBaczko2016_p4-6] Von Baczko & Desojo, 2016, p.4

[Martinez2018_p1-7] 1 2 Martínez et al., 2018, p.1

[table-12-1-234-8] 1 2 "Table 12.1," in Weishampel et al., 2004. p.234

[table-12-1-237-9] "Table 12.1," in Weishampel, et al., 2004. Page 237.

[Ezcurra2017-10] Ezcurra, 2017

[Coloradosphenodon-11] Gaetano, Leandro C.; Sotomayor Chacón, Juan C.; Arcaria, María R.; Vega, Nahuel; Leardi, Juan M.; Seoane, Federico D.; Otero, Alejandro (2026-09-05). "Earliest-diverging rhynchocephalian from Gondwana: a new sphenodontian from the Upper Triassic Los Colorados Formation (northwestern Argentina)". Scientific Reports. doi:10.1038/s41598-026-68493-8. ISSN 2045-2322.

[12] 2 km NE of La Esquina at Fossilworks.org

[13] Río de los Tarros tracksite at Fossilworks.org

[Leonardi1994_p25-14] Leonardi, 1994, p.25

[15] Leonardi locality 15 at Fossilworks.org