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Ferris Formation
Stratigraphic range: Maastrichtian-Danian
Type Geological formation
Underlies Hanna Formation
Overlies Medicine Bow Formation
Thickness 600–2,000 m (2,000–6,600 ft)
Primary Mudstone
Other Sandstone
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

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.

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 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.

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 of the Ferris Formation
Genus Species Location Stratigraphic position Abundance Notes Images
Ankylosaurus Indeterminate
Ankylosaurus magniventris reconstruction.png
Nodosauridae Indeterminate
Stygimoloch S. spinifer
Stygimoloch NT small.jpg
Thescelosaurus Indeterminate
Thescelosaurus filamented.jpg
Triceratops Indeterminate Ferris remains previously attributed to Triceratops have been subsequently identified as indeterminate chasmosaurine fossils


Saurischians of the Ferris Formation
Genus Species Location Stratigraphic position Abundance Notes Images
Ornithomimus O. sp.
"Ornithomimus" sp. by Tom Parker.png
Tyrannosaurus T. rex
Color key
Taxon Reclassified taxon Taxon falsely reported as present Dubious taxon or junior synonym Ichnotaxon Ootaxon Morphotaxon
Uncertain or tentative taxa are in small text; crossed out taxa are discredited.
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