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 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.
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.
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.
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.
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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