Placerias (meaning 'broad body')[2] is an extinct genus of dicynodonts that lived during the Carnian to the Norian age of the Triassic Period (230–215 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.
| Placerias | |
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| Skeleton | |
Scientific classification 
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| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Clade: | Synapsida |
| Clade: | Therapsida |
| Suborder: | †Anomodontia |
| Clade: | †Dicynodontia |
| Family: | †Stahleckeriidae |
| Subfamily: | †Placeriinae |
| Genus: | †Placerias Lucas, 1904 |
| Species: | †P. hesternus
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| Binomial name | |
| †Placerias hesternus Lucas, 1904
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Description
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Placerias was one of the largest herbivores in the Late Triassic, weighing up to 800–1,000 kilograms (1,800–2,200 lb).[3][4] The largest skull found had a length of 68 centimetres (26.8 in).[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.[7]
Discovery
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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.[8]
Placerias was originally considered the last of the dicynodonts, although other Late Triassic dicynodonts, such as Lisowicia[9] and Pentasaurus[10] have since been discovered.[a]
See also
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edit- ^ A report of a dicynodont fossil from the Cretaceous Period[11] proved to be neither Cretaceous nor a dicynodont; it proved to be a specimen of a diprotodontid marsupial that probably dates to the Pliocene or Pleistocene.[12]
References
edit- ^ Kent, Dennis V.; Olsen, Paul E.; Lepre, Christopher; Rasmussen, Cornelia; Mundil, Roland; Gehrels, George E.; Giesler, Dominique; Irmis, Randall B.; Geissman, John W.; Parker, William G. (October 16, 2019). "Magnetochronology of the Entire Chinle Formation (Norian Age) in a Scientific Drill Core From Petrified Forest National Park (Arizona, USA) and Implications for Regional and Global Correlations in the Late Triassic" (PDF). Geochemistry, Geophysics, Geosystems. 20 (11). American Geophysical Union: 4654–4664. Bibcode:2019GGG....20.4654K. doi:10.1029/2019GC008474. S2CID 207980627.
- ^ Paleofile. "Page on Placerias". Retrieved 20 February 2010.
- ^ 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. doi:10.3390/d14110973. ISSN 1424-2818.
- ^ a b 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.
- ^ 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.
- ^ 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. doi:10.1127/njgpa/231/2004/145. Archived from the original on 21 May 2023.
- ^ 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.
- ^ "Fossilworks: Placerias hesternus". fossilworks.org. Retrieved 17 December 2021.
- ^ 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. Bibcode:2020HBio...32..452R. doi:10.1080/08912963.2018.1499734. ISSN 0891-2963. S2CID 91926999.
- ^ Kammerer, Christian F (2018). "The first skeletal evidence of a dicynodont from the lower Elliot Formation of South Africa". Palaeontologia Africana. 52: 102–128. ISSN 2410-4418.
- ^ Thulborn, T.; Turner, S. (2003). "The last dicynodont: an Australian Cretaceous relic". Proceedings of the Royal Society of London B. 270 (1518): 985–993. doi:10.1098/rspb.2002.2296. PMC 1691326. PMID 12803915.
- ^ Knutsen, Espen M.; Oerlemans, Emma (January 2020). "The last dicynodont? Re-assessing the taxonomic and temporal relationships of a contentious Australian fossil". Gondwana Research. 77: 184–203. Bibcode:2020GondR..77..184K. doi:10.1016/j.gr.2019.07.011. S2CID 202908716.
