Therapods | Definition, Classification & Examples

Theropod dinosaurs come in a wide range of sizes from some of the largest dinosaurs to have walked on Earth to smaller dinosaurs which eventually evolved into modern birds. Although Tyrannosaurus rex was long considered to be the largest theropod, paleontologists have since discovered new species, such as Carcharodontosaurus, which weighed in at 33,345 pounds, and Gigantosaurus, also hefty at 30,438 pounds. The smallest non-avian theropods include Microraptor zhaoianus and Anchiornis huxleyi, which were roughly the size of a small bird, weighing in at 110 grams.

Herrerasaurus

The Genus Herrerasaurus contains some of the earliest dinosaur species found in the fossil record. A majority of the species found in this genus were discovered in northwestern Argentina in the Ischigualasto Formation and are considered to be examples of early saurischian dinosaurs. Roughly 3 to 5 meters in length, Herrerasaurus was a small carnivorous dinosaur which fed on small and medium sized animals. Herrerasaurus possessed strong hind limbs with adaptations indicative of swift running abilities, such as short thighs and long feet. Weighing around 400 pounds, Herrerasaurus was not the largest dinosaur during the Triassic, but its hunting abilities made it a considerable foe for other dinosaurs of the same period.

Illustration of Herrerasaurus

Ceratosaurus

Ceratosaurus translates as 'horned lizard' and derives it names from the row of sharp horns and armor on its head and back. With an estimated length of 6 to 7 meters and a weight of up to 1,200 pounds, Ceratosaurus represented one of the largest hunting dinosaurs of the late Triassic and Jurassic Periods. Possessing short forelimbs and long, muscular legs with three toes, Ceratosaurus was a swift runner with thin, blade-like teeth that were adapted for slicing through meat.

Illustration of Ceratosaurus

Tetanurae

Tetanurae is large group of theropod dinosaurs which possessed some of the most common morpohological characteristics found in theropods, such as a reduction in the fourth and fifth digits in the hands and the presence of a less flexible tail. Two of the most well-represented groups of Tetanurae include the Carnosauria and the Coelurosauria.

Carnosauria

Carnosaurs are named for their dietary strategy as meat eaters. Carnosaurs are characterized by several morphological adaptations including an overall increase in size, modifications of the pelvis and hind legs, large orbits, and a long, narrow skull. Some well-known examples of Carnosauria include Allosaurus, Spinosaurus, and Megalosaurus.

Illustration of Allosaurus

Coelurosauria

Coelurosauria contains the theropod dinosaurs most closely related to extant birds. Some of the main characteristics of Coelurosauria include arm elongation, hinge-like ankles, and either a fuzzy or feathery body covering. Coelurosauria are divided into three categories:

Maniraptora: birds and other coelurosaurs

• Long forelimbs (arms)
• Three-fingered hands
• Semi-lunate (half-moon shaped) bone in the wrist
• Fused clavicle and sternum
• Shortened, distally stiffened tail

Ornithomimidae: bird-like coelurosaurs

• Long forelimbs (arms)
• Long, slim hindlimbs (legs)
• Clamping hands

Tyrannosauridae: giant coelurosaurs

• Short deep jaws
• Sharp, curved teeth
• Short forelimbs (arms)

Coelurosauria include famous species such as Tyrannossaurus rex and Archaeopteryx.

Illustration of Archaeopteryx

Theropods are carnivorous, bipedal dinosaurs from the saurischian order. Although originally carnivorous hunters which preyed upon other contemporaneous dinosaurs of the Triassic and Jurassic periods, theropods eventually evolved to include species which utilized herbivorous, omnivorous, and piscivorous dietary strategies. Characterized by sharp, curved teeth, three-toed feet, digits with sharp claws, and long, hollow bones, theropods included a diverse range of body sizes, from large, terrestrial dinosaurs such as Megalosaurus and Allosaurus to smaller, bird-like species like microraptors. Theropods include several clades such as Herrerasaurus, Ceratosaurus, and Tetanurae. Tetanurae dinosaurs include famous Carnosaurs and Coelurosaurs such as Tyrannosaurus rex and Archaeopteryx, as well as other species which gave rise to modern bird species.