Historical Geology 102
Life in the Mesozoic II

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


Reptilian features
- hardshelled egg layers
- jaw, dental and pelvic structures are similar
- 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

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
- 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"
- 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

- "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

- "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

- "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?

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

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