BIO 113 — Dinosaurs
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Lab 9
Dinosaur Origins

Stem Ornithodirans


  • Members of the Ornithodira that don't belong to either Dinosauria or Pterosauria
  • Quadrupedal, with limbs held beneath body
  • Relatively long, narrow skull
  • Long neck
Teleocrater
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Basal Dinosaurs: Ornithischia

  • "Bird-hipped Dinosaurs" with pubis that points backwards
  • Predominantly herbivorous
  • Quadrupedality evolved multiple times independently from bipedal ancestors

Silesauridae
  • Formerly thought to be outside the Dinosauria (i.e. split off before the Ornithischia-Saurischia split)
  • Recent studies suggest they are the most basal Ornithischian dinosaurs
  • Small to medium sized
  • Quadrupedal, with long front and hind legs
  • Relatively long neck, small head
  • Mostly herbivorous (earliest forms were omnivores)
Dinosauromorphs
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Chilesaurus
  • Bipedal herbivore
  • Has been considered part of Theropoda, Sauropodomorpha, or Ornithischia
  • Most recent study suggests it is a basal Ornithischian (despite its late appearance)
  • Fairly long neck; small head
Basal Dinosaurs

Basal Dinosaurs: Saurischia

  • Saurischia are the "lizard-hipped dinosaurs" that includes the Sauropods and Theropods (and birds)
  • Included here are primitive dinosaurs that belong to the clade Saurischia but may fall outside either the Sauropodamorpha or Theropoda
  • Sometimes considered dinosauromorphs instead of true dinosaurs
  • Small to medium size with slender build
  • Bipedal, with longer hind legs than front legs

Herrerasauridae
  • Bipedal carnivores with fairly long hind legs
  • 3 functional fingers (4th vestigial and not visible externally)
  • Skull squarish
Tawa
  • Bipedal carnivore with fairly long hind legs
  • May be a basal Theropod or a Dinosauromorph
  • 3 functional fingers (4th vestigial and not visible externally)
  • Snout narrow, pointed
Herrerasaurus fossil
Herrerasaurus skeleton, Middle Triassic, Argentina (Museum of Ancient Life)
Basal Dinosaurs
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This page last updated 29 May 2023 by Udo M. Savalli ()
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