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The Popo Agie Formation (/poʊˈpoʊʒə/ poh-POH-zhə) is a Triassic geologic formation that crops out in western Wyoming, western Colorado, and Utah. It was deposited during the Late Triassic in fluvial (river) and lacustrine (lake) environments that existed across much of what is now the American southwest. The earliest known dinosaur of the Laurasian continent, Ahvaytum, is discovered from the Popo Agie Formation. Dinosaurian trace fossils and fragmentary fossils of prehistoric reptiles and amphibians, including pseudosuchian reptiles and temnospondyl amphibians, have also been reported from this formation.

Paleobiota

Amphibians

Reptiles

Taxon	Species	Member	Material	Notes	Images
Ahvaytum	A. bahndooiveche		UWGM 1975, a left astragalus, and UWGM 7549, a partial left femur	A probable sauropodomorph dinosaur and the oldest known Laurasian dinosaur
Heptasuchus	H. clarki		UW 11562, a partial skull and postcranial skeleton; UW 11563 through UW 11565, partial postcranial remains; both from Big Horn Mountains, Wyoming	A rauisuchian	(in background)
Beesiiwo	B. cooowuse		USNM 494329, a left maxilla and left dentary from Hole in the Wall, Wyoming; TxVP 46037.1, UWGM 7027 and UWGM 7028, maxillary fragments from Cottonwood Creek, Wyoming	A rhynchosaur, previously assigned to cf. Hyperodapedon sanjuanensis	(in foreground)
Poposaurus	P. gracilis		UR 358, a partial ilium from Lander, Wyoming; UR 357, a partial skeleton including vertebrae, hips, and limb bones	A bipedal poposauroid first described from the Popo Agie Formation and known from more complete specimens from the Chinle Formation
Sulcimentisauria indet.	Indeterminate		A partial left humerus and right femur	A 'silesaurid'

Synapsids

See also

• List of dinosaur-bearing rock formations
  • List of stratigraphic units with indeterminate dinosaur fossils

Footnotes

1. Locally "po-PO-zha" according to Don Pitcher, 2006, Moon Handbooks Wyoming, p. 269
2. More ambiguous transcription of "po-po-zsha" at "Popo Agie Wilderness". The National Wilderness Preservation System. Wilderness.net. Retrieved 2008-03-08.
3. High, L.R.; Hepp, D.M.; Clark, T.; Picard, M.D. (1969). "Stratigraphy of Popo Agie Formation (Late Triassic), Uinta Mountain Area, Utah and Colorado". Geologic Guidebook of the Uinta Mountains: Utah's Maverick Range (Sixteenth Annual Field Conference ed.). Utah Geological Association. pp. 181–192.
4. ^ Lovelace, David M; Kufner, Aaron M; Fitch, Adam J; Curry Rogers, Kristina; Schmitz, Mark; Schwartz, Darin M; LeClair-Diaz, Amanda; St.Clair, Lynette; Mann, Joshua; Teran, Reba (2025-01-01). "Rethinking dinosaur origins: oldest known equatorial dinosaur-bearing assemblage (mid-late Carnian Popo Agie FM, Wyoming, USA)". Zoological Journal of the Linnean Society. 203 (1): zlae153. doi:10.1093/zoolinnean/zlae153. ISSN 0024-4082.
5. ^ Sulej, T. (2002). "Species discrimination of the Late Triassic temnospondyl amphibian Metoposaurus diagnosticus" (PDF). Acta Palaeontologica Polonica. 47 (3): 535–546.
6. Gee, B. M.; Jasinski, S. E. (2021). "Description of the metoposaurid Anaschisma browni from the New Oxford Formation of Pennsylvania". Journal of Paleontology. 95 (5): 1061–1078. Bibcode:2021JPal...95.1061G. doi:10.1017/jpa.2021.30. S2CID 235546289.
7. Dawley, R.M.; Zawiskie, J.M.; Cosgriff, J.W. (1979). "A rauisuchid thecodont from the Upper Triassic Popo Agie Formation of Wyoming". Journal of Paleontology. 53 (6): 1428–1431.
8. Fitch, A. J.; Haas, M.; C’Hair, W.; Ridgley, E.; Ridgley, B.; Oldman, D.; Reynolds, C.; Lovelace, D. M. (2023). "A New Rhynchosaur Taxon from the Popo Agie Formation, WY: Implications for a Northern Pangean Early-Late Triassic (Carnian) Fauna". Diversity. 15 (4): 544. doi:10.3390/d15040544. hdl:10919/114487.
9. Lees, J.H. (1907). "The skull of Paleorhinus, a Wyoming phytosaur". The Journal of Geology. 15 (2): 121–151. Bibcode:1907JG.....15..121L. doi:10.1086/621382. JSTOR 30056366. S2CID 129850970.
10. Mehl, M.G. (1915). "Poposaurus gracilis, a new reptile from the Triassic of Wyoming". The Journal of Geology. 23 (6): 516–522. Bibcode:1915JG.....23..516M. doi:10.1086/622268. JSTOR 30067173.
11. Gauthier, J.A.; Nesbitt, S.J.; Schachner, E.R.; Bever, G.S.; Joyce, W.G. (2011). "The bipedal stem crocodilian Poposaurus gracilis: inferring function in fossils and innovation in archosaur locomotion" (PDF). Bulletin of the Peabody Museum of Natural History. 52 (1): 107–126. doi:10.3374/014.052.0102. S2CID 86687464. Archived from the original (PDF) on 2015-09-24.
12. Kammerer, C. F.; Fröbisch, J. R.; Angielczyk, K. D. (2013). Farke, Andrew A (ed.). "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. PMC 3669350. PMID 23741307.

References

• Weishampel, David B.; Dodson, Peter; and Osmólska, Halszka (eds.): The Dinosauria, 2nd, Berkeley: University of California Press. 861 pp. ISBN 0-520-24209-2.

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