Hell Creek Formation is one of the more famous and intensely
studied dinosaur fossil sites. Hell Creek is expansive, and
includes areas of Eastern Montana badlands, Northwestern South
Dakota, and Southwestern North Dakota. The strata’s
age ranges from about 65 to 70 million years old, and were
formed in a delta with a warm and moist climate. Interestingly,
the famous iridium enriched K-T boundary layer that separates
the Mesozoic from the Cenozoic occurs as thin, discontinuous
but distinct bedding plane near the top of the Formation.
The Hell Creek Formation biota is most famous for its dinosaurs,
most complete Hadrosaurid dinosaur ever found, but is otherwise
huge and diverse, encompassing plants, invertebrates, fish,
reptiles, and amphibians, and mammals. Bird (avian dinosaurs)
and pterosaur fossils have also been found, as well as the
teeth of sharks that were apparently tolerant to fresh water.
following dinosaurs and types have been discovered from Hell
Creek: Tyrannosaurus rex; Nanotyrannus lancensis; Troodon
formosus; Dromaeosaurid; Ornithomimus; Nodosaurids; Edmontonia;
Denversaurus schlessmani; Thescelosaurus; neglectus; Thescelosaurus
sp.; Edmontosaurus regalis; Edmontosaurus annectens; Anatotitan
copei; Pachycephalosaurids, Pachycephalosaurus wyomingensis,
Ceratopsids; Triceratops horridus; and Torosaurus latus.