Thecodonts & Dinosaurs

Small, agile reptiles with long tails, short limbs
Bipedal and quadruped varieties
Ancestors of the dinosaurs
Dinosaur means "terrible lizard"
The name implies reptiles
- not completely accurate
- there are similarities and differences

Dinosaurs

Reptilian features
- hardshelled egg layers
- jaw, dental and pelvic structures are similar
Differences
- endothermic (warm-blooded) ??
Closely related to reptiles but are as different from reptiles as birds are different from reptiles

First Dinosaur

Herrerasaurus or Staurikosaurus
Both belonged to the group Saurischia
- pelvic structure similar to modern reptiles
Two main Saurischian groups
- Theropods and Sauropods
Ornithischia (other main dinosaur group)
- pelvic structure similar to birds

Saurischian Theropods

Carnivorous dinosaurs
Bipedal locomotion
Sizes ranged from 60 cm to 15 meters
2 kg to 8 tons
Tyrannosaurs largest terrestrial carnivore ??
- skull length 1 meter
- 15 cm long teeth, serrated edge
Deinonychus - "terrible claw"
- large claw on hind foot
Theropod stance
- classic view is upright, plodding
- modern interpretation - horizontal body, tail off the ground, more efficient runner

Saurischian Sauropods

Herbivores
Quadrupeds
20 to 35 meters in length (average size)
10 to 55 tons
Largest land animals to ever exist
Camarasaurs - "brontosaurus"
- short, heavy skull with blunt snout typically
- forelimbs are longer than hind limbs
Diplodocus
- skull is long and slender, with teeth towards the front
- longer body lengths than Camarasaurs
Largest known Sauropods
- Brachiosaurus 55 tons
- Supersaurus 42 meters long

Ornithischian "Ornithopods"

"bird feet"
 
Iguanodonts
- first dinosaur to be scientifically described in 1825
- bipedal herbivores, some quadrupeds
- massive hind limbs
- heavy shoulders and forelimbs
- many possessed a spike-like "thumb"
- skull - long snout; toothless beak in front; rows of teeth in back of jaw

Hadrosaurs
- "duckbilled" dinosaurs
- last major group of dinosaurs to evolve
-best known, best studied of all dinosaurs skull
- broad toothless beak
- rows of teeth in back
- Hadrosaur skin impression

Edmontosaurs and Parasaurolophus
- two groups of Hadrosaurs
- Parasaurolophus - also called crested Hadrosaurs

Armored and Plated Dinosaurs
- herbivores
- quadrupeds

Stegosaurs
- "plated lizards"
- Has a row of armor plates along back
- Small skulls with a very small brain case - 2.5 to 2.9 oz. brain for a 1 to 2 ton animal
- Short, massive forelimbs with long hind limbs

Ankylosaurs
- "fused lizards"
- fused vertebra segment
- small skulls
- Body was covered with small round or square armor plates
- spikes or spines also common
- Often possessed a large bony mass at the end of the tail
- Defense or Deception?

Ceratops
- Large, distinctive skulls characterized by one or three horns and a large frill at the back of the skull
- Triceratops
- Brachyceratops

Additional Readings in This Topic

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