Ferris Formation

Ferris Formation Stratigraphic range: Late Cretaceous
Type	Geological formation
Underlies	Hanna Formation
Overlies	Medicine Bow Formation
Thickness	600-2,000 m
Lithology
Primary	mudstone
Other	sandstone
Location
Region	North America

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.

The Ferris Formation is up to 2,000 m thick in the Hanna Basin and represents 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.

Vertebrate paleofauna

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

Myledaphus,

Lissodus,

Cretorectolobus,

Phylodus,

Amia,

Lepisosteus,

Basilemys,

Adocus,

Leptochamops,

Brachychampsa,

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

Ornithischians

Color key Taxon Reclassified taxon Taxon falsely reported as present Dubious taxon or junior synonym Ichnotaxon Ootaxon Morphotaxon		Notes Uncertain or tentative taxa are in small text; crossed out taxa are discredited.

Ornithischians of the Ferris Formation
Genus	Species	Location	Stratigraphic position	Abundance	Notes	Images
Ankylosaurus[2]	Indeterminate[2]					Thescelosaurus
Nodosauridae[3]	Indeterminate[2]
Stygimoloch[2]	S. spinifer[2]
Thescelosaurus[2]	Indeterminate[2]
Triceratops[2]	Indeterminate[2]				Ferris remains previously attributed to Triceratops have been subsequently identified as indeterminate chasmosaurine fossils.[2]

Saurischians

Color key Taxon Reclassified taxon Taxon falsely reported as present Dubious taxon or junior synonym Ichnotaxon Ootaxon Morphotaxon		Notes Uncertain or tentative taxa are in small text; crossed out taxa are discredited.

Saurischians of the Ferris Formation
Genus	Species	Location	Stratigraphic position	Abundance	Notes	Images
Ornithomimus[4]	O. sp.[4]					Tyrannosaurus
Tyrannosaurus[2]	T. rex[2]

See also

• List of dinosaur-bearing rock formations

Footnotes

1. Wroblewski (1995).
2. "3.12 Wyoming, United States; 9. Ferris Formation," in Weishampel, et al. (2004). Page 585.
3. Listed as "Edmontonia cf. rugosidens" in "3.12 Wyoming, United States; 9. Ferris Formation," in Weishampel, et al. (2004). Page 585.
4. Listed as "Ornithomimus cf. velox" in "3.12 Wyoming, United States; 9. Ferris Formation," in Weishampel, et al. (2004). Page 585.

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.
• 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, p. 61A.