Placerias Explained

Placerias (meaning 'broad body')[1] is an extinct genus of dicynodonts that lived during the Carnian to the Norian age of the Triassic Period (230–220 million years ago). Placerias belongs to a group of dicynodonts called Kannemeyeriiformes, which was the last known group of dicynodonts before the taxon became extinct at the end of the Triassic.

Description

Placerias was one of the largest herbivores in the Late Triassic, measuring 3.5m (11.5feet) long and weighing up to 800kg-1000kgkg (1,800lb-2,000lbkg).[2] [3] [4] The largest skull found had a length of 68cm (27inches).[5]

Placerias had a powerful neck, strong legs, and barrel-shaped body with possible ecological and evolutionary parallels with the modern hippopotamus, spending much of its time during the wet season wallowing in the water and chewing at bankside vegetation.[4] Placerias was closely related to Ischigualastia and similar in appearance.[6] Placerias used its beak to slice through thick branches and roots with two short tusks that could be used for defence and for intra-specific display. The genus exhibits two morphs, one with short tusks and one with long tusks, which is inferred to be sexual dimorphism, with the longer-tusked individuals presumably being males.

Discovery

Fossils of forty Placerias were found near St. Johns, southeast of the Petrified Forest in the Chinle Formation of Arizona. This site has become known as the 'Placerias Quarry' and was discovered in 1930, by Charles Camp and Samuel Welles, of the University of California, Berkeley. Sedimentological features of the site indicate a low-energy depositional environment, possibly flood-plain or overbank. Bones are associated mostly with mudstones and a layer that contains numerous carbonate nodules. It is also known from the Pekin Formation of North Carolina.[7] Placerias was originally considered the last of the dicynodonts until fossil finds from Queensland were reported in 2003 to have revealed that the dicynodonts survived until the Early Cretaceous.[8] Agnolin et al. (2010) called for a reconsideration of that Australian specimen, noting its similarity to baurusuchian crocodyliforms such as Baurusuchus pachecoi.[9] The Cretaceous dicynodont specimen was eventually discovered to belong to a specimen of Diprotodon instead.[10] The giant dicynodont Lisowicia also survived into the late Triassic.[11]

See also

External links

Notes and References

  1. Web site: Page on Placerias. Paleofile. 20 February 2010.
  2. Book: Prothero, Donald R. . 20. Synapsids: The Origin of Mammals. Vertebrate Evolution: From Origins to Dinosaurs and Beyond . 18 April 2022 . CRC Press . Boca Raton . 978-0-36-747316-7. 10.1201/9781003128205-4 . 246318785 . en.
  3. 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 . en . 14 . 11 . 973 . 10.3390/d14110973 . 1424-2818. free .
  4. 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. 10.2307/3515510. 3515510 . 0883-1351.
  5. Green . Jeremy . Schneider . Vince . Schweitzer . Mary . Clarke . Julia . 2005-09-07 . NEW EVIDENCE FOR NON-PLACERIAS DICYNODONTS IN THE LATE TRIASSIC (CARNIAN-NORIAN) OF NORTH AMERICA . Journal of Vertebrate Paleontology . 25 . 65A–66A.
  6. Vega-Dias . Cristina . Maisch . Michael W. . Schultz . Cesar Leandro . 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 . 2 March 2004 . 231 . 2 . 145–166 . 10.1127/njgpa/231/2004/145 . https://web.archive.org/web/20230521073426/https://www.schweizerbart.de/papers/njgpa/detail/231/90103/A_new_phyologenetic_analysis_of_Triassic_dicynodon . 21 May 2023 .
  7. Web site: Fossilworks: Placerias hesternus. fossilworks.org. 17 December 2021.
  8. Thulborn . T. . Turner . S. . 2003 . The last dicynodont: an Australian Cretaceous relic . Proceedings of the Royal Society of London B . 270 . 1518 . 985–993 . 10.1098/rspb.2002.2296 . 12803915 . 1691326.
  9. Agnolin . F. L. . Ezcurra, M. D. . Pais, D. F. . Salisbury, S. W. . 2010 . A reappraisal of the Cretaceous non-avian dinosaur faunas from Australia and New Zealand: Evidence for their Gondwanan affinities . Journal of Systematic Palaeontology . 8 . 2 . 257–300 . 10.1080/14772011003594870. 2010JSPal...8..257A . 130568551 .
  10. Knutsen . Espen M. . Oerlemans . Emma . The last dicynodont? Re-assessing the taxonomic and temporal relationships of a contentious Australian fossil . Gondwana Research . January 2020 . 77 . 184–203 . 10.1016/j.gr.2019.07.011 . 2020GondR..77..184K . 202908716 .
  11. Racki . Grzegorz . Lucas . Spencer G. . 2020-04-20 . Timing of dicynodont extinction in light of an unusual Late Triassic Polish fauna and Cuvier's approach to extinction . Historical Biology . 32 . 4 . 452–461 . 10.1080/08912963.2018.1499734 . 2020HBio...32..452R . 91926999 . 0891-2963.

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