Theropoda

Tyrannosaurus rex by Todd Marshall (2004)

CHARACTERISTICS

• All theropods were bipedal, with functional grasping hands
• Flexible lower jaw with an additional joint midway, between the dentary and post-dentary bones, to allow the animal to fit larger chunks of food in its mouth
• Limb bones were all hollow, so lightening the skeleton
• All theropods but one group (the therizinosaurs) were carnivores with sharp serrated teeth
• Nearly all had three-fingered hands (tridactly)
• Most primitive forms: Herrerrasauridae
  • Could be a non-theropodan dinosaur because it retained primitive features: two sacral vertebrae, archaic structure of the cervical (neck) vertebrae, third finger is longer than the second finger
  • Theropodan features include a joint between the jaw and skull, and long grasping hands

Cladogram provided by T.Holtz Jr. 2004 (http://www.geol.umd.edu/~tholtz/G104/10422ther.htm)

EUTHEROPODA (3)- "True unquestioned theropods"

CHARACTERISTICS

• Grasping hands with only three fingers
• Three-toed foot
• Furcula (clavicles fused into a wishbone)
• An extra opening in the skull called the promaxillary fenestra

Coelophysis bauri by Todd Marshall (2004)

(1) COELOPHYSOIDEA - These animals were common during the Late Triassic and Early Jurassic periods, but were replaced by more advanced theropods during the Late Jurassic. Many had ornamental head crests.

• Long thin neck, and kinked snout
• Examples: Coelophysis, Dilophosaurus

Dilophosaurus by P. Olsen (2004) based on Paul (1988)

(2) CERATOSAURIA

• Shorter more robust skulls with thick bull-like necks
• Extremely short arms, hands, and fingers
• Pleurocoels (hollow spaces) present in the neck vertebrae
• Hips are fused in adult forms
• An increased number of sacral (hip) vertebrae
• Some forms had crests and horns
• Examples: Abelisauridae, Ceratosaurus

(3) TETANURAE "stiff tails" (2)

These theropods were more advanced than the ceratosaurs, and coelophysoids.

• The caudal vertebrae (tail) are stiffened or interlocking to provide more balance and maneuverability while running
• All of the teeth are located in the front of the snout
• Large, grasping hands
• Presence of maxillary fenestra (large opening in the skull)
• Cavities on both sides of the dorsal (back) vertebrae
• A boot-shaped expansion at the end of the pubis

Allosaurus fragilis by Todd Marshall (2004)

(1) SPINOSAUROIDEA (2)

• (1) MEGALOSAURIDAE
  • Best known are the Carcharodontosauridae

Megalosaurus by Todd Marshall (2004)

• (2) SPINOSAURIDAE
  • Long crocodile-like skulls with teeth that are round in cross-section
  • Sails or fins evident in some species
  • Examples: Spinosaurus and Baryonyx

(2) AVETHEROPODA (2)

• Maxillary fenestra (extra opening in the skull between the snout and eye socket) are present
• A complex system of air sacs and chambers within the skeleton
• Large grasping hands, with three fingers
• Furcula (wishbone) and sternum (breastbone)

(1) CARNOSAURS

• Largest of the theropods
• Skull: large nares, very large orbits (eye sockets), and some had ornamental crests
• Some species had extra openings in the skull near the snout
• Examples: Allosaurus, Giganotosaurus

Allosaurus maximus by Todd Marshall (2004)

(2) COELUROSAURIA

• Coelurosaurs had the largest brain sizes of any dinosaurs, and fenestrae (openings) in the roof of the mouth
• Long and slender extremities, with three toes and fingers
• Astragalus (main ankle bone) has a long process at the front, locking it to the base of the tibia
• The chevrons in the tail are 'boat-shaped' in order to make the tail more rod-like
• Feathers present - although they are only filaments in basal coelurosaurs
• Examples: Compsognathus, Ornitholestes

NEXT : COELUROSAURIA

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Author: Emma Schachner
Last updated: 13 November 2004
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