Los Colorados Formation

For other uses, see Colorado Formation.

Los Colorados Formation
Stratigraphic range: Norian ~227–213 Ma PreꞒ Ꞓ O S D C P T J K Pg N
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	29.8°S 67.9°W / -29.8; -67.9
Approximate paleocoordinates	38.9°S 31.4°W / -38.9; -31.4
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.^[1] Magnetostratigraphic analysis suggests that the Los Colorados Formation was deposited between 227 and 213 million years ago.^[2]

Description

Extent of the formation in the Ischigualasto-Villa Unión Basin

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.^[2]

Fossil content

Anapsids

Anapsids of Los Colorados Formation
Genus	Species	Location	Material	Notes	Images
Palaeochersis	P. talampayensis			[3][4]

Synapsids

Synapsids of Los Colorados Formation
Genus	Species	Location	Material	Notes	Images
Chaliminia	C. musteloides			[3]
Jachaleria	J. colorata		A skull and complete jaws.	A Kanemyeriidae dicynodont.
Tessellatia	T. bonapartei		A partial skull, including the snout, orbital region, and lower jaws.	A cynodont.[5]

Archosauromorphs

Archosauromorphs of Los Colorados Formation
Genus	Species	Location	Material	Notes	Images
Fasolasuchus	F. tenax	La Rioja Province	A fragmented skull and jaws.	A giant loricatan Pseudosuchian.[1][3]
Neoaetosauroides	N. engaeus	Quebrada de los Jachaleros, El Salto (San Juan)		An aetosaur.[3]
Riojasuchus	R. tenuisceps			An ornithosuchid.[3][6]

Crocodylomorpha

Crocodylomorphs of Los Colorados Formation
Genus	Species	Location	Material	Notes	Images
Coloradisuchus	C. abelini	La Rioja Province		[7]
Hemiprotosuchus	H. leali	Quebrada de los Jachaleros, El Salto (San Juan)		[3][7]
Pseudhesperosuchus	P. jachaleri	Quebrada de los Jachaleros, El Salto (San Juan)		[3]

Dinosaurs

Indeterminate theropod remains present in the Provincia de la Rioja.^[1]

Dinosaurs of Los Colorados Formation
Genus	Species	Location	Material	Notes	Images
Coloradisaurus	C. brevis	La Rioja Province[1]	"Skull, adult"[3][8]	A massospondylid sauropodomorph.
Lessemsaurus	L. sauropoides	La Rioja Province[1]	"Partial cervical, dorsal, and sacral vertebrae, adult."[8]	A sauropodiform.
Prosauropoda	Indeterminate	La Rioja & San Juan Provinces	Includes Strenusaurus procerus.[1] "Dorsals, caudals, partial fore- and hindlimb."[9]
Powellvenator	P. podocitus	Ischigualasto-Villa Unión Basin	Known from previously undescribed partial hindlimbs	A coelophysoid.
Riojasaurus	R. incertus	La Rioja Province		A sauropodomorph.[10][3][1]
Zupaysaurus	Z. rougieri	La Rioja Province		An early theropod.[3][1]

Ichnofossils

• cf. Brachychirotherium sp.^[11]
• Chirotherium sp.^[12][13]

See also

• List of dinosaur-bearing rock formations
• Quebrada del Barro Formation, contemporaneous fossiliferous formation of the Marayel-El Carrizal Basin just southeast of the Ischigualasto-Villa Unión Basin
• Caturrita Formation, contempeoraneous fossiliferous formation of the Paraná Basin, southeastern Brazil
• Chinle Formation, contemporaneous fossiliferous formation of Arizona
• Elliot Formation, contemporaneous fossiliferous formation of the Karoo Basin, South Africa
• Fremouw Formation, contemporaneous fossiliferous formation of Antarctica

References

1. Weishampel et al., 2004, pp.527-528
2. Kent et al, 2014, p.7959
3. Arcucci et al., 2004, p.561
4. 2 km NE of La Esquina at Fossilworks.org
5. 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): Article number 6451. Bibcode:2022NatSR..12.6451G. doi:10.1038/s41598-022-10486-4. PMC 9038739. PMID 35468982.
6. Von Baczko & Desojo, 2016, p.4
7. Martínez et al., 2018, p.1
8. "Table 12.1," in Weishampel et al., 2004. p.234
9. "Table 12.1," in Weishampel, et al., 2004. Page 237.
10. Ezcurra, 2017
11. Río de los Tarros tracksite at Fossilworks.org
12. Leonardi, 1994, p.25
13. Leonardi locality 15 at Fossilworks.org

Bibliography

• Arcucci, A.B.; Marsicano, C.A.; Caselli, A.T. (2004), "Tetrapod association and palaeoenvironment of the Los Colorados Formation (Argentina): a significant sample from western Gondwana at the end of the Triassic", Geobios, 37 (5): 557–568, Bibcode:2004Geobi..37..557A, doi:10.1016/j.geobios.2003.04.008, hdl:11336/97772, retrieved 2019-03-28
• 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
• Kent, Dennis V.; Santi Malnis, Paula; Colombi, Carina E.; Alcober, Oscar A.; Martínez, Ricardo N. (2014), "Age constraints on the dispersal of dinosaurs in the Late Triassic from magnetochronology of the Los Colorados Formation (Argentina)", Proceedings of the National Academy of Sciences, 111 (22): 7958–7963, Bibcode:2014PNAS..111.7958K, doi:10.1073/pnas.1402369111, PMC 4050597, PMID 24843149
• 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
• Weishampel, David B.; Dodson, Peter; Osmólska, Halszka (2004), The Dinosauria, 2nd edition, Berkeley: University of California Press, pp. 1–880, ISBN 0-520-24209-2, retrieved 2019-02-21

Further reading

• A. B. Arcucci and R. A. Coria. 2003. A new Triassic carnivorous dinosaur from Argentina. Ameghiniana 40(2):217-228
• J. F. Bonaparte. 1999. Evolución de las vértebras presacras en Sauropodomorpha [Evolution of the presacral vertebrae in Sauropodomorpha]. Ameghiniana 36(2):115-187
• 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
• J. F. Bonaparte. 1981. Descripción de "Fasolasuchus tenax" y su significado en la sistematica y evolución de los thecodontia. Revista del Museo Argentino de Ciencias Naturales "Bernardino Rivadavia" 3(2):55-101
• J. F. Bonaparte. 1978. Coloradia brevis n. g. et n. sp. (Saurischia–Prosauropoda), dinosaurio Plateosauridae de la Formacion Los Colorados, Triasico Superior de La Rioja, Argentina [Coloradia brevis n. g. et n. sp. (Saurischia–Prosauropoda), a plateosaurid from the Upper Triassic Los Colorados Formation of La Rioja, Argentina]. Ameghiniana 15(3-4):327-332
• J. F. Bonaparte. 1971. Los tetrapodos del sector superior de la Formacion Los Colorados, La Rioja, Argentina (Triásico Superior) [The tetrapods of the upper part of the Los Colorados Formation, La Rioja, Argentina (Upper Triassic)]. Opera Lilloana 22:1-183
• J. F. Bonaparte. 1969. Dos nuevas "faunas" de reptiles triasicos de Argentina [Two new reptilian "faunas" of the Argentine Triassic]. Gondwana Stratigraphy (IUGS Symposium, Buenos Aires) 2:283-306
• J. B. Desojo and A. M. Baez. 2007. Cranial morphology of the Late Triassic South American archosaur Neoaetosauroides engaeus: evidence for aetosaurian diversity. Palaeontology 50:267-276
• J. B. Desojo and A. M. Baez. 2005. El esqueleto postcraneano de Neoaetosauroides (Archosauria: Aetosauria) del Triásico Superior del centro-oeste de Argentina. Ameghiniana 42:115-126
• 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
• G. W. Rougier, M. S. de la Fuente, and A. B. Arcucci. 1995. Late Triassic turtles from South America. Science 268:855-858