Ischigualastia

Ischigualastia
Temporal range: Late Carnian,
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An Ischigualastia jenseni replica skeleton on display in Japan.
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Clade: Synapsida
Clade: Therapsida
Clade: †Anomodontia
Clade: †Dicynodontia
Family: †Stahleckeriidae
Subfamily: †Stahleckeriinae
Genus: †Ischigualastia
Cox 1962
Type species
†Ischigualastia jenseni
Cox, 1962

Ischigualastia is an extinct genus of large dicynodont therapsids from the Late Triassic of Argentina. It is named after its place of discovery, the Ischigualasto Formation in the Ischigualasto-Villa Unión Basin of northwestern Argentina.[1] Like other Late Triassic dicynodonts, Ischigualastia is a member of the family Stahleckeriidae.[2][3][4][5]

Discovery

Ischigualastia was briefly named by C. Barry Cox in 1962,[6] with a larger description published in 1965.[1] It is one of the better-known South American dicynodonts in terms of its variety of fossils, including several nearly complete skulls.[1][7][4] Cox named the genus after its location of discovery, the Ischigualasto Valley, while the species honors James Jensen, who prepared some of its fossils.[6]

The holotype, MACN 18.055, is a skull stored at the Museo Argentino de Ciencias Naturales "Bernardino Rivadavia" (MACN) in Buenos Aires. Though partially "restored" with plaster, it still closely resembles unaltered skulls.[4] Cox (1965) also discussed Ischigualastia fossils collected by the Museum of Comparative Zoology (MCZ) in Cambridge, Massachusetts.[1] Additional fossils are housed at the Instituto Miguel Lillo (PVL) in Tucumán and Universidad Nacional de San Juan (PVSJ) in San Juan. However, they have yet to be fully described.[4]

There are a few reports of Ischigualastia fossils from New Mexico, Texas, and India: a femur, a snout fragment, and a poorly-preserved skull, respectively. These claims have not held up to scrutiny, since the fossils in question do not closely resemble Ischigualastia in particular.[8][4] Supposed Ischigualastia fossils from Brazil are more likely to be Jachaleria, Sangusaurus,[4] or a new unnamed species.[3]

Description

Ischigualastia is a very large dicynodont, with a deep skull bearing pointed projections on each side of the snout, rather than tusks. The skull could reach a length of 60 cm (2.0 ft).[4] The back of the skull is steeply sloped and has particularly large spaces for vertical jaw muscles, suitable for a strong bite. In contrast, many earlier tusked dicynodonts had low skulls which were better suited for propalinal (front-to-back) jaw movement during a bite.[2]

In many regards Ischigualastia is similar to a nearby relative, Jachaleria, though there are a few traits entirely unique to the skull of Ischigualastia. The top of the snout has a narrow depression near where the frontal bones contact the nasal bones. The pineal foramen, a hole further back on the forehead, has swollen rims. Finally, the zygomatic arch (roughly equivalent to the cheekbone) is deep and strongly bent upwards.[4]

Ischigualastia is similar in stature to the North American stahleckeriid Placerias,[9] which measured around 3.5 metres (11 ft) long and weighed up to 800–1,000 kilograms (1,800–2,200 lb).[10][11][12] Ischigualastia, Stahleckeria, and Placerias all show evidence of sexual dimorphism, meaning that there are strong differences between the skulls of proposed males and females.[4][13] Robust Ischigualastia skulls, interpreted as males, have a distinctly broader snout and intertemporal area, as well as rough patches on the nasal bones.[4]

Paleoecology

Ischigualastia was a large quadrupedal herbivore found in late Carnian-age strata of the Ischigualasto Formation (La Peña, Cancha de Bochas, and earliest Valle de la Luna members). It was a relatively common component of the local fauna, although not as abundant as the medium-sized herbivores Hyperodapedon and Exaeretodon.[7] It was one of the two dicynodonts which lived in the Ischigualasto Formation, the other being Jachaleria, a close relative which is only found in the youngest layers of the formation. The largest carnivores in the formation were the pseudosuchian Saurosuchus and the common predatory dinosaur Herrerasaurus.[7]

Ischigualastia and Placerias were each among the last and largest dicynodonts of the Late Triassic, though they were surpassed in both regards by Lisowicia, a huge late-surviving stahleckeriid from Poland.

See also

References

  1. ^ a b c d Cox, C.B. (1965-03-04). "New Triassic dicynodonts from South America, their origins and relationships". Philosophical Transactions of the Royal Society of London. Series B, Biological Sciences. 248 (753): 457–514. Bibcode:1965RSPTB.248..457C. doi:10.1098/rstb.1965.0005. ISSN 2054-0280. S2CID 86293260.
  2. ^ a b Ordonez, Maria de los Angeles; Cassini, Guillermo H.; Vizcaíno, Sergio F.; Marsicano, Claudia A. (2019). "A geometric morphometric approach to the analysis of skull shape in Triassic dicynodonts (Therapsida, Anomodontia) from South America". Journal of Morphology. 280 (12): 1808–1820. Bibcode:2019JMorp.280.1808O. doi:10.1002/jmor.21066. ISSN 0362-2525. PMID 31621947.
  3. ^ a b Maisch, Michael W. (2021). "An unusual historic dicynodont specimen (Therapsida: Dicynodontia) from the Dinodontosaurus Assemblage Zone of the Santa Maria Formation (Middle Triassic) of Rio Grande do Sul, Brazil". PalZ. 95 (1): 129–144. Bibcode:2021PalZ...95..129M. doi:10.1007/s12542-020-00525-8. ISSN 0031-0220.
  4. ^ a b c d e f g h i j Kammerer, Christian F.; Ordoñez, Maria de los Angeles (2021). "Dicynodonts (Therapsida: Anomodontia) of South America". Journal of South American Earth Sciences. 108 103171. Bibcode:2021JSAES.10803171K. doi:10.1016/j.jsames.2021.103171. ISSN 0895-9811.
  5. ^ Carroll, Robert L. (1988). Vertebrate Paleontology and Evolution. W.H. Freeman and Company. ISBN 0-7167-1822-7.
  6. ^ a b Cox, C. Barry (1962). "Preliminary diagnosis of Ischigualastia, a new genus of dicynodont from Argentina". Breviora. 156: 8–9.
  7. ^ a b c Martínez, Ricardo N.; Apaldetti, Cecilia; Alcober, Oscar A.; Colombi, Carina E.; Sereno, Paul C.; Fernandez, Eliana; Malnis, Paula Santi; Correa, Gustavo A.; Abelin, Diego (2013). "Vertebrate succession in the Ischigualasto Formation". Journal of Vertebrate Paleontology. 32 (Memoir 12: Basal sauropodomorphs and the vertebrate fossil record of the Ischigualasto Formation (Late Triassic: Carnian-Norian) of Argentina, sup1): 10–30. doi:10.1080/02724634.2013.818546. hdl:11336/7771. ISSN 0272-4634. S2CID 37918101.
  8. ^ Kammerer, Christian F.; Fröbisch, Jörg; Angielczyk, Kenneth D. (2013-05-31). "On the Validity and Phylogenetic Position of Eubrachiosaurus browni, a Kannemeyeriiform Dicynodont (Anomodontia) from Triassic North America". PLOS ONE. 8 (5) e64203. Bibcode:2013PLoSO...864203K. doi:10.1371/journal.pone.0064203. ISSN 1932-6203. PMC 3669350. PMID 23741307.
  9. ^ Vega-Dias, Cristina; Maisch, Michael W.; Schultz, Cesar Leandro (2 March 2004). "A new phylogenetic analysis of Triassic dicynodonts (Therapsida) and the systematic position of Jachaleria candelariensis from the Upper Triassic of Brazil". Neues Jahrbuch für Geologie und Paläontologie - Abhandlungen. 231 (2): 145–166. Bibcode:2004NJGPA.231..145V. doi:10.1127/njgpa/231/2004/145. Archived from the original on 21 May 2023.
  10. ^ Prothero, Donald R. (18 April 2022). "20. Synapsids: The Origin of Mammals". Vertebrate Evolution: From Origins to Dinosaurs and Beyond. Boca Raton: CRC Press. doi:10.1201/9781003128205-4. ISBN 978-0-36-747316-7. S2CID 246318785.
  11. ^ Hartman, Scott A.; Lovelace, David M.; Linzmeier, Benjamin J.; Mathewson, Paul D.; Porter, Warren P. (November 2022). "Mechanistic Thermal Modeling of Late Triassic Terrestrial Amniotes Predicts Biogeographic Distribution". Diversity. 14 (11): 973. Bibcode:2022Diver..14..973H. doi:10.3390/d14110973. ISSN 1424-2818.
  12. ^ Fiorillo, Anthony R.; Padian, Kevin; Musikasinthorn, Chayanin (2000). "Taphonomy and Depositional Setting of the Placerias Quarry (Chinle Formation: Late Triassic, Arizona)". PALAIOS. 15 (5): 373–386. doi:10.2307/3515510. ISSN 0883-1351. JSTOR 3515510.
  13. ^ Pinto, James L.; Marshall, Charles R.; Nesbitt, Sterling J.; Latorre, Daniel Varajão de (2024-05-31). "Quantitative evidence for dimorphism suggests sexual selection in the maxillary caniniform process of Placerias hesternus". PLOS ONE. 19 (5): –0297894. Bibcode:2024PLoSO..1997894P. doi:10.1371/journal.pone.0297894. ISSN 1932-6203. PMC 11142433. PMID 38820280.
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