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1. What are Archosaurs, and what features define them?
Archosaurs include crocodiles, pterosaurs, and dinosaurs (including birds).
Shared traits:
Antorbital fenestra (opening in front of the eye).
Mandibular fenestra (opening in the lower jaw).
Thecodont teeth (teeth set in sockets).
Sigmoidal (S-shaped) femur for upright posture.
2. What defines a dinosaur?
Cnemial crest on the tibia – A ridge for muscle attachment, aiding leg extension.
Perforate acetabulum – A hole in the hip socket allowing for an upright stance.
3. What are the two major groups of dinosaurs?
Ornithischia ("bird-hipped") – Pubis points backward.
Saurischia ("lizard-hipped") – Pubis points forward (ancestral trait).
4. What are key features of Ornithischians?
All herbivorous.
Predentary bone forming a beak.
Cheeks for better food processing.
5. What are the three major groups of Ornithischians?
Thyreophora ("shield bearers") – Armored dinosaurs (stegosaurs, ankylosaurs).
Ornithopoda ("bird foot") – Hadrosaurs, iguanodonts.
Marginocephalia ("margin heads") – Pachycephalosaurs, ceratopsians.
6. What are characteristics of Thyreophorans?
Quadrupedal with bony armor (osteoderms).
Two groups:
Stegosaurs – Plates/spikes, short forelimbs.
Ankylosaurs – Heavy armor, some with tail clubs.
7. What are the two subgroups of Ankylosaurs?
Ankylosaurids: Broad beak, cranial horns, tail club.
Nodosaurids: Narrow beak, no tail club.
8. What are characteristics of Ornithopods?
Bipedal or facultative quadrupeds.
Jaw joint below the tooth row – Allows better chewing efficiency.
Hadrosaurs ("duck-billed dinosaurs") – Had elaborate crests for vocalization.
9. What are characteristics of Marginocephalians?
Bony elaborations on the skull.
Two main groups:
Pachycephalosaurs ("thick-headed lizards") – Thick skulls, head-butting behavior.
Ceratopsians ("horned-faced ones") – Frills, beaks, often quadrupedal.
10. How did ceratopsians evolve over time?
Early forms (e.g., Psittacosaurus) were bipedal and small.
Later forms (e.g., Triceratops) became large, quadrupedal, with elaborate skulls.