Ferris Formation
Stratigraphic range: Maastrichtian-Danian ~66–63 Ma PreꞒ Ꞓ O S D C P T J K Pg N ↓
Type	Geological formation
Underlies	Hanna Formation
Overlies	Medicine Bow Formation
Thickness	600–2,000 m (2,000–6,600 ft)
Lithology
Primary	Mudstone
Other	Sandstone
Location
Coordinates	41°48′N 106°36′W / 41.8°N 106.6°W / 41.8; -106.6
Approximate paleocoordinates	48°48′N 82°12′W / 48.8°N 82.2°W / 48.8; -82.2
Region	Wyoming
Country	United States
Extent	Hanna Basin
Ferris Formation (the United States) Show map of the United States Ferris Formation (Wyoming) Show map of Wyoming

The Ferris Formation is a Late Cretaceous (~66 Ma) to Paleocene (66-63 Ma), fluvial-deltaic geological formation in southern Wyoming. It contains a variety of trace and body fossils, preserved in sandy fluvial channel deposits and overbank units. Dinosaur remains are fragmentary, but include Triceratops, Tyrannosaurus, dromaeosaurids, Paronychodon, Ricardoestesia, Edmontosaurus, Edmontonia, Ankylosaurus, and Pachycephalosaurus.^[1]

Some of the fluvial channels contain evidence of tidal influence and brackish water, in the form of tidal facies, shark teeth, and shrimp burrows. This demonstrates that the western shoreline of the Western Interior Sea was still within a few hundred kilometers even during the latest Cretaceous. The local K-T boundary is contained within a sandy channel deposit made up of stacked bars. Reworked Cretaceous fossils are preserved at the base of the channel complex, associated with mud rip-up clasts, and Paleocene mammal fossils are preserved in the upper portion of the bar.^[2]

The Ferris Formation is up to 2,000 metres (6,600 ft) thick in the Hanna Basin and represents a rapid accumulation of predominantly fine-grained sediment on a broad delta. The delta previously fed the deepwater Lewis Shale and shallow marine Fox Hills Formation. The Ferris followed behind as a system of lagoons, bays, and delta plain environments.

In addition to a variety of dinosaurs, the following taxa are known from the Ferris Formation:

and a variety of Cretaceous and Paleocene multituberculates, marsupial, and placentals.

Ornithischians of the Ferris Formation
Genus	Species	Location	Stratigraphic position	Abundance	Notes	Images
Ankylosaurus[3]	Indeterminate[3]
Nodosauridae[4]	Indeterminate[3]
Stygimoloch[3]	S. spinifer[3]
Thescelosaurus[3]	Indeterminate[3]
Triceratops[3]	Indeterminate[3]				Ferris remains previously attributed to Triceratops have been subsequently identified as indeterminate chasmosaurine fossils[3]

Saurischians of the Ferris Formation
Genus	Species	Location	Stratigraphic position	Abundance	Notes	Images
Ornithomimus[5]	O. sp.[5]
Tyrannosaurus[3]	T. rex[3]

• List of dinosaur-bearing rock formations
• Hell Creek Formation
• Fort Union Formation

• Weishampel, David B.; Dodson, Peter; Osmólska, Halszka (2004), The Dinosauria, 2nd edition, Berkeley: University of California Press, pp. 1–880, ISBN 0-520-24209-2, retrieved 2019-02-21
• Wroblewski, Anton F. (1995), "First report of changes in lower vertebrate faunas across the Cretaceous-Tertiary boundary, western Hanna Basin, Wyoming", Journal of Vertebrate Paleontology, Supp. to volume 15: 61A
• Lillegraven, Jason A.; Eberle, Jaelyn J. (1999), "Vertebrate Faunal Changes through Lancian and Puercan Time in Southern Wyoming", Journal of Paleontology, 73 (4): 691–710, Bibcode:1999JPal...73..691L, doi:10.1017/S0022336000032510, JSTOR 1306768, retrieved 2020-11-16