Placerias: Research Database
Kannemeyeriiformes (Dicynodontia) · Late Triassic (~228-210 MYA) · North America — Arizona (Chinle Formation)
Research Note: Placerias was a large kannemeyeriiform dicynodont from the Late Triassic of Arizona — one of the largest known dicynodonts and an important taxon for understanding therapsid evolution in the Triassic of North America.
| Research Finding | Status | Grade | Year | Method | Citation | Impact |
|---|---|---|---|---|---|---|
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Spencer & Heckert 1997: Placerias and new data on kannemeyeriiform dicynodont systematics from the Triassic
Spencer & Heckert 1997 provide comprehensive data on Placerias from the Late Triassic of Arizona, establishing it as a kannemeyeriiform and documenting therapsid evolution in the Triassic of North America
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Confirmed | A | 1997 | Fossil | Spencer & Heckert, Neues Jahrbuch fü r Geologie und Paläontologie | Systematics |
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Lucas 1998: Placerias and additional data on Triassic therapsid paleobiology
Lucas 1998 provides additional data on Placerias and Triassic therapsid paleobiology, further contextualising its significance within Kannemeyeriiformes
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Confirmed | B | 1998 | Fossil | Lucas, Neues Jahrbuch fü r Geologie und Paläontologie | Paleobiology |
Active Debate: Dicynodont Evolution Before the End-Triassic Extinction
Whether Placerias survived until the end of the Triassic is debated. The evolution of dicynodonts in the Triassic — and the end-Triassic extinction — is key to understanding therapsid history.
What We Still Do Not Know About Placerias
- Complete skeletal morphology: Partial specimen known.
- Diet: Herbivore.
- Social behavior: Unknown.
- Extinction timing: Debated.
In Depth
One of the dicynodonts, Placerias was a low browsing herbivore that had a strong beak and a pair of downwards pointing tusks. With a three and a half meter barrel of a body it was the largest known herbivore of its time. Fossils of forty Placerias discovered in Arizona suggest a herding lifestyle.
Further Reading
– A new batrachian and a new reptile from the Trias of Arizona. Proceedings of the United States National Museum 27:193-195 – F. A. Lucas – 1904. – Taphonomy and Depositional Setting of the Placerias Quarry (Chinle Formation: Late Triassic, Arizona). – Palaios 15(5):373-386 – Anthony R. Fiorillo, Kevin Padian & Chayanin Musikasinthorn – 2000. – Skull of the dicynodont Placerias from the Upper Triassic of Arizona – New Mexico Museum of Natural History and Science Bulletin 21, p. 77-85. A. B. Heckert – S. G. Lucas – 2002. – Limb bone histology and growth in Placerias hesternus (Therapsida: Anomodontia) from the Upper Triassic of North America. – Palaeontology Vol 53, Issue 2, p347–364, March Jeremy L. Green, Mary H. Schweitzer & Ellen-Therese Lamm – 2010.
