Theropds make up the group of dinosaurs that contain the Tyrannosaurus rex, Velociraptors, and modern birds. Theropods are visually distinct from other dinosaur groups with their three-toed feet and the way they walk exclusively on their hind legs. The theropod body plan emerged in the Late Triassic with varieties like the Coelophysis, which was fairly small. By the Jurassic, giants like the Allosaurus became the dominant predators, while smaller theropods like the Archaeopteryx developed flight feathers and learned to fly. The largest theropod was the Tyrannosaurus rex who dominated the American West during the Cretaceous period.
During the age of the dinosaurs, theropods were the major predators of the land. Different species developed their own ways of hunting, some went solo like the T. rex and some in groups like the Compsognathus, but they all benefited from agile, dextrous body plans. For years, paleontologists believed that theropods were slow-moving with tails dragging on the ground– in reality, theropods were able to move with speed and agility, their long tails counterbalancing their heads and necks. Many had sharp teeth, but others like the Struthiomimus had a beak like modern theropods (birds).
The theropods are the only group of dinosaurs with living members. Thanks to their small size, mobility, and diverse diets, at least a few birds managed to survive the grueling years following the K-pg Impact. Since then, they have flourished as today, birds actually outnumber humans about 6 to 1.
The Sauropod family is mainly comprised of quadrupedal (walking on four feet), slow moving, long-necked dinosaurs. Sauropods are known for their calm and generally pacifistic demeanor, and were generally herbivorous. Sauropods species came in a wide range of sizes from the diminutive Ohmdenosaurus, which only grew about 13 feet long to the biggest of the Titanosaurs like the Patagotitan mayorum which grew up to a whopping 121 feet long (that’s longer than a blue whale).
Sauropods were big eaters, requiring literal tons of fresh vegetation per day to survive. Their long necks allowed them to reach leaves from tall trees and low growing shrubbery before swallowing their food without stopping to chew it. Their long necks also helped them keep an eye out for predators. Fossil evidence also suggests that sauropods moved in herds and utilized a somewhat complex social structure arranged by age. A site of Mussaurus patagonicus fossils showed evidence of communal egg-laying grounds as well as proof that juveniles congregated into ‘schools’ while adults grazed near the herd alone or in pairs.
The idea that birds are dinosaurs is still relatively fresh in the general zeitgeist, but paleontologists have been investigating this connection since the discovery of the first fossils of Archaeopteryx lithographica were unearthed in 1861. Since then, more fossils have been found which further support the link between birds and theropod dinosaurs of old.
Like some modern birds, they ate small mammals, lizards, amphibians, and insects. Unlike modern birds, the Archaeopteryx had teeth instead of a hard beak. It also had claws at the bend of its wings that scientists think they used to grab onto trees as they glided through the canopy. As for flight, there is still a debate over whether they could truly take flight as easily as modern birds. It is possible that they relied on gliding from tree to tree like a sugar glider or required a running start with little hops to take off flying.
Compsognathus was a genus of small theropod dinosaur that lived in Europe during the Jurassic period. Compsognathus, sometimes nicknamed ‘Compie’, is among the smallest dinosaurs, not accounting for modern birds, growing anywhere between 2 and 3 feet in length and weighing up to 8 lbs. The Solnhofen specimen was even smaller, about 30 inches long from nose to tail and weighing between 1 and 3 lbs, but this specimen was later determined to be a juvenile. It is thought that the Compsognathus would use its speed, agility, and sharp teeth to ambush small prey like lizards, insects, and possibly even small pterosaurs. Unlike their depiction in popular media, it is unlikely that they hunted in socially active groups.
(Late Jurassic)
The Brachiosaurus was a large sauropod dinosaur from the late Jurassic famous for its long, upright neck. Brachiosaurus were herbivorous and likely moved in herds which helped keep them safe from predators. They used their high vantage point to keep an eye out for danger and to access vegetation that grew higher up in the trees. They ate hundreds of pounds of leaves, branches, and other plant matter a day to sustain their large size. It is theorized that a Brachiosaurus could live around 100 years due to its size and slow-moving lifestyle.
Pictured here is the centrum of a Brachiosaurus vertebra.
The Lufengosaurus was a relative to the larger sauropods like Brachiosaurs but was smaller with a shorter neck and tail. Despite their smaller size (about 30 feet from nose to tail), they were still able to reach vegetation from the trees by standing up on their hind legs for short periods of time.
The Camarasaurus was a medium to large sauropod genus from North America. The name Camarasaurus references the animal’s unique chambered vertebrae which aided in its respiratory system. The Camarasaurus had a slightly shorter neck and tail relative to other sauropods and had a boxy head and powerful jaw. It is believed that Camarasaurus’ bite force was among the strongest of all the sauropods and was used to break twigs and eat tough conifers.
The Allosaurus was a large (28 to 30 feet) predatory theropod dinosaur that lived in North America, Europe, and possibly even Africa and Australia. These apex predators had sharp teeth with which could bite and tear at soft tissue rather than rely on a strong bite force like some other theropods like T. rex. They also had large claws on its ‘hands’ used to grapple and subdue prey items. Allosaurus possessed two horns or crests on their brow, likely used as visual display or species recognition as opposed to fighting.
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 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.
Dakotaraptor was a mid-sized carnivorous theropod dinosaur discovered in the South Dakota region of the Hell Creek Formation. At an estimated 16 feet in length from nose to long feathered tail, the Dakotaraptor bridges the gap between the gigantic tyrannosaurids like the Nanotyrannus and smaller theropods like the Pectinodon. The Dakotaraptor is the second largest raptor species discovered, only dwarfed by the Utahraptor. Most of fossils found of this animal are individual teeth.
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.
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.
Titanosaurs were a group of large, long-necked dinosaurs in the Sauropod family that contained the largest land animals the world has ever seen. Even the smallest Titanosaurs were huge, growing about 23 feet long and weighing about 11 tons (22,000 lbs.) Amongst the largest Titanosaurs, Patagotitan mayorum could grow to 137 feet and weighed 70-77 tons (about as heavy as 10 to 14 African Elephants). Suffice it to say, these things were big.
Titanosaurs were widespread and their fossils have been found on all continents (even antarctica!), but the largest species lived primarily in modern Patagonia (hence the name Patagotitan) and Argentina.
Psittacosaurus was a genus of small Ceratopsian dinosaurs from the Early Cretaceous. On average, members of the Psittacosaurus genus grew to about 6.5 feet long and walked on its hind legs similar to a Theropod dinosaur. The Psittacosaurus has been well preserved and studied, leading paleontologists to make conclusions about them and their behaviors. For example, fossils of congregated young Psittacosaurus hatchlings show that baby Psittacosaurus may have stayed in groups, similar to modern ducklings. One Psittacosaur specimen was so well preserved that it still possessed a cloaca, an anatomic structure shared by reptiles and birds which acts as the single opening for their urinary, digestion, and reproductive tracks. This same fossil also provided evidence for skin coloration and the presence of quills that ran along the base of their tails.
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.
Hadrosaurs, often called “duck-billed dinosaurs”, were herbivorous herding dinosaurs that lived in North America, Europe, and Asia during the late Cretaceous period. Hadrosaurs were grazers and had ‘dental batteries’ or stores of new teeth that would replace the old ones as they wore down. Paleontologists have been able to study Hadrosaur skin impressions to discern that their skin was scaly and bumpy. Many hadrosaurs had large head crests, some of which had hollow chambers inside. Some scientists think that species like the Parasaurolophus used its hollow head crest to amplify verbalizations, creating a loud horn-like call. Hadrosaurs typically walked on all four legs, but they were able to stand up on the larger hind legs at will.
Spinosaurus was a large theropod dinosaur whose fossils are found in modern-day Morocco and Egypt. Spinosaurus spent a lot of time near, and possibly in, the waters of the Mediterranean Sea. From its long and conical teeth, we can tell that it ate mostly fish, and many scientists think it possessed a large sail down its spine that may have attracted potential mates. Spinosaurus was at least semi-aquatic as it had a paddle-shaped tail that might have been used to propel itself like a modern crocodile, but scientists haven’t yet come to an agreement on whether they were good swimmers or if they spent much time in deep water.
Charcharodontosaurus was a very large meat-eating theropod dinosaur that lived in the northern part of Africa. This dino was big—slightly taller and longer than the T. rex but with a smaller body mass with more slender skeletal structures. The name Charcharodontosaurus is a reference to Charcharodon, the genus of sharks that contains the Great White Shark because they have similar shaped teeth.
Velociraptors have been heavily featured in the Jurassic Park and Jurassic World sagas and are depicted as scaly, mid-sized terrors of the dinosaur world. This depiction is not strictly accurate, at least in regard to appearance. Velociraptors were considerably smaller than you might think (3 feet tall and 5 feet long) and possessed feathers much like their modern bird relatives. Velociraptors, like all raptors, had a large specialized toe claw on each foot which they would have used to hold down prey, similar to modern predatory birds.
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