Chañares Formation

Chañares Formation
Stratigraphic range: Carnian
~235–234 Ma
↓
Type Geologic formation
Unit of Agua de la Peña Group
Underlies Ischicuca Formation
Overlies Tarjados Formation
Lithology
Primary Claystone
Location
Coordinates 29°48′S 67°48′W / 29.8°S 67.8°W / -29.8; -67.8Coordinates: 29°48′S 67°48′W / 29.8°S 67.8°W / -29.8; -67.8
Approximate paleocoordinates 49°54′S 37°48′W / 49.9°S 37.8°W / -49.9; -37.8
Region La Rioja Province
Country  Argentina
Extent Ischigualasto-Villa Unión Basin

The Chañares Formation is geologic formation located in La Rioja Provence, Argentina.

It was originally thought to be formed during the Ladinian age of the Middle Triassic epoch, in the Triassic Period of the Mesozoic Era; Marsicano et al. (2016) dated it to early Carnian (235–234 Ma), Late Triassic.[1]

The formation overlies the Tarjados Formation and is overlain by the Ischicuca Formation. The formation belongs to the Agua de la Peña Group of the Ischigualasto-Villa Unión Basin, where it is exposed in the Ischigualasto Provincial Park, a World Heritage site in Argentina.[2] The formation of claystones and tuff was deposited in a fluvial to lacustrine environment.[3]

Fossil content

Some localities are well known for their abundance of tetrapod fossils. Theraspids include the kannemeyeriid Dinodontosaurus, and cynodonts such as Probainognathus and Massetognathus, the latter being the most abundant tetrapod taxon in the formation.[4]

Other notable tetrapods present from the formation are the archosaurs. Ornithodirans include Lewisuchus,[5] Lagerpeton,[6] Marasuchus,[7] and Pseudolagosuchus.[8]

Other archosaurs include Gracilisuchus[9] and Luperosuchus.[10] Three proterochampsids are known from the formation, Tropidosuchus, Chanaresuchus, and Gualosuchus. They are very similar in appearance, but differ in size and cranial proportions.[11]

In 2018, plant remains and palynomorphs preserved in the coprolites produced by large dicynodonts, and a study on their implications for inferring the diet of dicynodonts from the formation were described.[12] Also tetrapod burrows, likely produced by small eucynodonts, were described.[13]

Other fossils

Other fossils found in the formation include:[3][14]

See also

References

  1. ↑ Claudia A. Marsicano; Randall B. Irmis; Adriana C. Mancuso; Roland Mundil; Farid Chemale (2016). "The precise temporal calibration of dinosaur origins". Proceedings of the National Academy of Sciences of the United States of America. 113 (3): 509–513. doi:10.1073/pnas.1512541112. PMC 4725541. PMID 26644579.
  2. ↑ Kent et al, 2014, p.7959
  3. 1 2 Chañares Tetrapod Assemblage at Fossilworks.org
  4. ↑ Romer, A. S. (1967). "The Chañares (Argentina) Triassic reptile fauna. III. Two new gomphodonts, Massetognathus pascuali and M. teruggii". Breviora. 264: 1–25.
  5. ↑ Romer, A. S. (1972). "The Chañares (Argentina) Triassic reptile fauna; XIV, Lewisuchus admixtus, gen. et sp. nov., a further thecodont from the Chañares beds". Breviora. 390: 1–13.
  6. ↑ Romer, A. S. (1971). "The Chañares (Argentina) Triassic reptile fauna. X. Two new but incompletely known long-limbed pseudosuchians". Breviora. 378: 1–10.
  7. ↑ Sereno, P. C.; Arcucci, A. B. (1994). "Dinosaurian precursors from the Middle Triassic of Argentina: Marasuchus lilloensis, gen. nov". Journal of Vertebrate Paleontology. 14 (1): 53–73. doi:10.1080/02724634.1994.10011538.
  8. ↑ Arcucci, A. B. (1987). "Un nuevo Lagosuchidae (Thecodontia-Pseudosuchia) de la fauna de Los Chañares (Edad Reptil Chañarense, Triasico Medio), La Rioja, Argentina". Ameghiniana. 24 (1–2): 89–94.
  9. ↑ Romer, A. S. (1972). "The Chañares (Argentina) Triassic reptile fauna. XIII. An early ornithosuchid pseudosuchian, Gracilisuchus stipanicicorum, gen. et sp. nov". Breviora. 389: 1–24.
  10. ↑ Romer, A. S. (1971). "The Chañares (Argentina) Triassic reptile fauna. VIII. A fragmentary skull of a large thecodont, Luperosuchus fractus". Breviora. 373: 1–8.
  11. ↑ Romer, A. S. (1971). "The Chañares (Argentina) Triassic reptile fauna. XI. Two new long-snouted thecodonts, Chanaresuchus and Gualosuchus". Breviora. 379: 1–22.
  12. ↑ Pérez et al., 2018
  13. ↑ Fiorelli et al., 2018
  14. ↑ Agua Escondida at Fossilworks.org

Bibliography

Further reading

  • A. Arcucci and C. A. Marsicano. 1999. A distinctive new archosaur from the Middle Triassic (Los Chanares Formation) of Argentina. Journal of Vertebrate Paleontology 19:228-232
  • R. R. Rogers, A. B. Arcucci, F. Abdala, P. C. Sereno, C. A. Forster and C. L. May. 2001. Paleoenvironment and taphonomy of the Chañares Formation tetrapod assemblage (Middle Triassic), northwestern Argentina: spectacular preservation in volcanogenic concretions. Palaios 16:461-481
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