Little is known about the Paronychodon. The only fossils found as of yet of this group of theropds are teeth like the one pictured here. These mysterious carnivorous dinosaurs lived in North America during the late Cretaceous, and similar teeth have also been found in Eurasia, which may indicate that this genus could have been fairly far spread.
The Nanotyrannus is a newly confirmed genus of therapod dinosaur that lived alongside the Tyrannosaurus rex at the end of the Cretaceous period. For years, scientists debated over whether this smaller was a teenage T. rex or its own distinct species. In 2025, the researchers at North Carolina Museum of Natural Sciences determined that the theropod in their famous fossil “The Dueling Dinosaurs” was fully-grown at the time of death. This discovery settled the debate once and for all. Now that the two species are officially split, our understanding of both the Nanotyrannus and the T. rex are forever changed.
One of the most famous and beloved dinosaurs, the Tyrannosaurus rex, was the king of Hell Creek back during the late Cretaceous. Its name translates to “king of the tyrant lizards”, which it earned by being one of the biggest theropod dinosaurs (12 feet tall and 40 feet long) and possessing the greatest bite force of any land animal ever (8,000 – 12,800 lbs. per square inch). The T. rex is often noted for its large head full of long sharp teeth which was ideal for taking big bites out of its big prey like the Triceratops or Edmontosaurus.Its small arms are also cause for conversation; some scientists think their small (approx. 3 feet) arms were a trade-off for its large head, which was much more useful than long arms would have been considering its very large prey items. It is also possible that T. rex simply ‘grew out’ of their arms, as younger T. Rex specimens have for more proportional limbs.
At Earth Experience, you can see a full-scale T. rex model named Frank and get a feel for just how big these tyrants were.
The Champsosaurus was a large aquatic reptile that lived in slow-moving freshwater rivers, swamps, and ponds during the Cretaceous period and into the Paleogene epoch. Champsosaurus was an odd-looking animal, with a crocodile-like body and an elongated snout which was useful in ambush hunting for fish. Despite their similarities to crocodilians, they are not closely related.
The Triceratops was a tank-sized herbivore that lived up to the end of the age of the dinosaurs. The Triceratops had several defining features like its three horns used to defend against T. rex attacks and a beak it used to shear tough plants to eat. The purpose of its large fan-like structure on the back of its head called the ‘frill’ is still a matter of debate. Some think the frill was a defensive measure to protect its neck from the devastating bite of a T. rex, while others think it likely displayed distinctive colors or patterns to attract mates and be recognizable to other Triceratops. There are even theories that it was used as thermoregulation, as the frill was full of veins that could have allowed the animal’s blood to cool.
At Earth Experience, we have been lucky enough to be able to work on a Triceratops skull from the Hell Creek Formation in Montana. Our specimen is likely a subadult, meaning that even with its large size, full grown Triceratops would still be slightly bigger. Due to erosion, our skull is missing its horns, which is unfortunately common with Triceratops fossils. It does still have a lot of its frill still protected in its plaster jacket until more of the base skull is prepared and stabilized. Come see this work-in-progress in person!
Amongst the fossil bones and teeth of dinosaurs, paleontologists occasionally find fossilized dinosaur egg material. As you might expect, dinosaur eggs are rarely found due to their delicate nature, and it is generally hard to determine what type of dinosaur may have once been inside. However, finding the eggs, or better yet, the nests tell us a lot about dinosaur behavior. Some fossils of Oviraptor dinosaurs have been found on top of their eggs, indicating that they cared for their eggs like modern birds. Other larger species buried their eggs rather than brood as their weight would have done more harm than good.
With modern technology, our understanding of dinosaur eggs has improved further. It is possible to perform a CT scan on dinosaur eggs, which makes it possible for scientists to learn more about dinosaur embryos and their development.
Pectinodon bakkeri was a small bird-like dinosaur in the theropod family. Little is known for certain about the Pectinodon due to scant fossil evidence aside from the animal’s comb-like teeth. By comparing the teeth to other small theropods, it is assumed that Pectinodons was a small, agile, feathered predator. Its few fossils have largely come from the Lance Formation in Wyoming.
Little is known about the Richardoestesia because there has not been a lot of fossil evidence for this morphogenus. What is known about this group comes from fossil teeth like the one pictured here, which have been found in Southern Canada, Northwest United States, and even in some locations in Asia and Europe. From the teeth found, scientists believe this group of dinosaurs were carnivorous theropods. More fossil evidence needs to be found before more conclusions can be drawn about this mysterious group.
Pachycephalosaurus was a bipedal herbivorous dinosaur which is best known for its odd, dome-shaped growth on top of its head. Scientists have not yet come to an agreement on what their hard heads were used for; some think they may have used them to ram others of their species, while others think it was for display to impress potential mates. Others yet think their noggins were used for a combination of the two.
The Ankylosaurus was a large, armored dinosaur that lived in North American during the Cretaceous period. The Ankylosaurus was like a living tank, covered in spiky osteoderms (bony-plates) which protected it from large predators like the T. rex, and had a large club tail which they would use as a bone-cracking weapon against predators or fellow Ankylosaurus. Ankylosaurus were herbivores and ate low growing vegetation like ferns, horsetails, and fallen fruit.
One of the best-preserved dinosaur specimens ever found was a Borealopelta, another genus of Ankylosaur, which still has the osteoderms, some skin, and even the stomach contents of its last meal preserved. You can learn more about this specimen and even see it in person at the Royal Tyrell Museum in Alberta, Canada.
Thescelosaurus was a genus of ornithischian (bird-hipped) dinosaurs that made its home in North America. Thescelosaurs were beaked herbivores that grew to be 10-13 feet long. By studying its cranial structure, scientists have come to believe that the Thescelosaurus relied on a keen sense of smell to find buried roots and tubers to eat.
Stygimys is a genus of extinct mammals that originated in the Late-Cretaceous and lived in North America and Northeastern Asia. Like most mammals of the time, they were small and rodent-like in nature and belonged to the multituberculates, which is a now extinct order of mammals defined by their unique, knobby teeth.
Didelphodon was an omnivorous and likely scavenging mammal that lived during the Cretaceous period. It was one of the largest mammals at the time, yet only grew about 3 feet long. It had sharp teeth and a strong bite force, which helped it crack the shells of turtles, clams, and snails. It also likely ate eggs, aquatic vegetation, and the carcasses of dinosaurs.
Struthiomimus was a mid-sized theropod dinosaur (about 13 feet from beak to tail). The name Struthiomimus literally translates to “ostrich mimic”, which is an apt name, as this dinosaur heavily resembled modern flightless birds. Besides its ostrich-like appearance, the Struthiomimus is perhaps best known for its estimated speed. Scientists think these animals could run 30-50 miles per hour, similar to modern Grizzly Bears, Lions, and conveniently, ostriches.
Coniophis precedens was roughly 7cm long and one of – if not the – first ever snake species. Coniophis precedens acts as a ‘missing-link’ species, demonstrating that snakes diverged from terrestrial lizards as opposed to marine reptiles. Like modern snakes, it had no limbs, but it had not yet developed the jaw structure found in modern snakes which allows them to eat larger prey. This means that Coniophis precedens would have had to eat smaller prey items like salamanders and lizards.
Habrosaurus dilates is an extinct type of salamander whose fossils are commonly found in the Lance and Hell Creek Formations in the Western United States and Southern Part of Canada. It was about the size of a modern Hellbender salamander and munched on small, shelled animals like crayfish or snails. Habrosaurus dilates was one of the lucky species that survived the K-pg Impact extinction event.
Myledaphus bipartitus was a freshwater ray whose fossils have been found in Western United States and Canada. Myledaphus bipartitus was related to modern rays and guitarfish. Most of the fossils found have been fossil teeth which were used to crush the shells of clams and other bivalves.
Gar fish are long-bodied freshwater fish who possess armored scales along their bodies. Gars belonging to Lepisosteidae first developed in the early Cretaceous, but ancestors to these Gar first show up in the fossil record during the Jurassic Period. Gars are often called ‘living fossils’ as they have gone virtually unchanged over the last 100 million years. There is plenty of fossil evidence for the Gar in the Hell Creek Formation; their armored scales fossilize very well and appear a bit like shards of obsidian among the dirt.
Cyclurus fragosus was a species of bowfin fish that is most often found in the Hell Creek Formation.Cyclurus are thought to be the closest relatives of modern bowfins, but much smaller than their extant counterparts, only growing between 4 and 12 inches long.
The Edmontosaurus annectens was a species of Hadrosaur that lived during the Cretaceous period in the modern US and Canada. Many Edmontosaurus annectens fossils come from the Hell Creek Formation, where they lived among Triceratops, T. rex, and other smaller ceratopsians and theropods.
One of the only dinosaur fossils ever found in Tennessee was a chevron (a part of the spine) from what is thought to be Edmontosaurus annectens. It is likely that the animal had died near or in a river and was washed out into the Western Interior Seaway where it fossilized. You can see this chevron at Earth Experience Museum.
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