Dinosaurs of the Hell Creek Formation

The Treasure Trove of Fossils in North America

Dinosaurs may be extinct from the face of the planet, but they are alive and well in our imaginations.

- Steve Miller

A bit about the fantastic creatures we know and love that have captured the imagination of millions......Dinosaurs

Dinosaurs have caught the attention of millions in our world, whether it be a small child visiting a museum for the first time, a movie goer watching the fabled Jurassic Park movies, or the professional paleontologists whose job it is to uncover, excavate, and study these amazing creatures. They are extinct creatures that have caught the public's eye unlike any other creatures on our planet. But what exactly are dinosaurs?

Dinosaurs were a group of reptiles that made their mark in history during the Mesozoic Era, which is a unit of geologic time in our earth's history often referred to as the "age of dinosaurs". "The Mesozoic Era spans from 252 million years ago to 66 million years ago." (Geologyin). The Mesozoic Era is divided into 3 separate periods, going from oldest to youngest is the Triassic, Jurassic, and Cretaceous. "Dinosaurs evolved into a very diverse group of animals with a vast array of physical features, including modern birds" (American Museum of Natural History). During this time, some non-avian dinosaurs evolved into avian dinosaurs, the oldest ancestors of present-day birds. Dinosaurs became the dominant species on the planet until an asteroid hit the area of the present-day Gulf of Mexico, wiping out relatively all non-avian dinosaurs with aid from volcanic eruptions. What species were dominant before the dinosaur's extinction? Where can we find the closest point in time before the extinction event to learn more about these dinosaurs? The answer lies within the Hell Creek Formation in North America.

The Hell Creek Formation

A geologic formation is a unit of rock that has a consistent set of physical characteristics, also known as lithology. One of these formations is the Hell Creek Formation, which lays within the boundaries of Montana, Wyoming, North Dakota, and South Dakota. The Formation's geologic time is that of the Late Cretaceous period, when Dinosaurs were said to be at their peak. "The Latest Cretaceous, Hell Creek and Lance Formations are some of the most fossil-rich rock units in the United States, if not the world" (Virtual Dinosaur Museum). The Hell Creek is treasure trove for paleontologists, where famous fossils are found such as Triceratops and Hadrosaurs, but most notably the world famous and most recognizable dinosaur of all, Tyrannosaurus Rex.

The Map to the right shows the exposed Hell Creek Formation recorded in 2023 (State Geologic Map Compilation - Geology). The Hell Creek formation is made up sedimentary clastic rocks and date around to 66-67 million years ago. Having a rock unit so close to the time of extinction of the dinosaurs allows Paleontologists to find out what life was like for North American dinosaurs at the latest moment in their evolutionary progression through the Mesozoic Era.

The Dinosaurs of the Hell Creek Formation

The Hell Creek Formation has an abundance of dinosaurs, with a large species diversity that has allowed Paleontologists to keep going on digs and uncovering new specimens and even species every year. Most notable specimens include Triceratops, Edmontosaurus, and the world-renowned Tyrannosaurus Rex.

Triceratops

Triceratops were large herbivores dinosaurs, falling under the ceratopsian family, which means "Horned Face". The name Triceratops means three horned face, which fits as they had two massive horns positioned above their eyes along with a shorter horn above the snout. The horns are believed to have been used for display and dominance display in their herds. Many fossilized remains were found with T-rex teeth marks in them, leading the idea that T-rex and Triceratops often fought.

Edmontosaurus was one of the largest species of Hadrosaurids, aka duck-billed dinosaurs, that have ever existed. They had long muscular tails and powerful hindlimbs along with shorter forelimbs. Unlike other Hadrosaurids, Edmontosaurus didn't possess a bony crest like other members of its family like Corythosaurus. Some specimens have been found with skin impressions, so Paleontologists now know the texture of the skin of Edmontosaurus.

One of the World's most recognizable animals, even more than some of today's current animals, is the famed Tyrannosaurus Rex, the "Tyrant Lizard King". T-rex was a predatory therapod, a mostly carnivorous group of dinosaurs that were mostly bipedal. It was one of the largest terrestrial animals to ever exist in earth's history, especially for land predators. Most Tyrannosaurus specimens were discovered in the Hell Creek Formation of North America. It had incredibly strong neck and face muscles, which allowed it to have one of the greatest bite forces on the planet. Its muscular jaw and teeth were made for crushing bone with each bite, allowing it to take down large herbivores such as Hadrosaurs and Ceratopsians.

Other species that are notable are the Ankylosaurus, Pachycephalosaurus, Troodon, and Ornithomimus.

The Map to the right displays the exposed Cretaceous sediments in green (Geology of North America), along with the Hell Creek Formation which is situated along it. It is worth noting that same data points aren't within the exposed parts of the Hell Creek Formation but are still part of it as the fossils were found beneath the rock units and formations above them. Each specimen has a designated lithology that they were found in, ranging from primarily sandstones to shales and mudstones. All of which are sedimentary rocks found within the Hell Creek Formation and Upper Cretaceous boundary.

To this Day, the Hell Creek Formation produces numerous fossils of dinosaurs from the Late Cretaceous Period, where we find some of the closest living dinosaurs to our time. Through the study of these fossils and the Hell Creek Formations lithology, Paleontologists are able to reconstruct what life may have been like back in the day 66-67 million years ago. Back in a time when Dinosaurs ruled the earth, diverse species of these majestic creatures walked the lands we now live upon. By looking into the past and into the geologic time of the Hell Creek formation, Paleontologists aim to uncover the secrets and environment of the prehistoric world that was ruled by dinosaurs.

References and Maps Used.

Geologic Time Scale: Major Eons, Eras, Periods and Epochs. www.geologyin.com/2014/12/geologic-time-scale-major-eons-eras.html.

‌American Museum of natural history. “Dinosaur Facts | American Museum of Natural History.” American Museum of Natural History, 2019, www.amnh.org/dinosaurs/dinosaur-facts.

“The Paleobiology Database.” Paleobiodb.org, paleobiodb.org/#/.

‌“PaleoAdventures Database.” Virtualdinosaurmuseum.org, 2014, virtualdinosaurmuseum.org/HellCreek.html. Accessed 5 Dec. 2024.

‌U.S Geologic Survey. State Geologic Map Compilation - Geology. 13 Jan. 2023, services2.arcgis.com/FiaPA4ga0iQKduv3/arcgis/rest/services/State_Geologic_Map_Compilation_%E2%80%93_Geology/FeatureServer. Accessed 1 Dec. 2024.

‌Esri. Geology of North America. 11 Mar. 2022, services.arcgis.com/P3ePLMYs2RVChkJx/arcgis/rest/services/Geology_of_North_America/FeatureServer. Accessed 10 Oct. 2024.

‌Dinosaur data points (Hell Creek Dinosaurs) were plotted by Christian Noble, undergrad at MSU, using Paleodatabase data.

Triceratops