Thyreophora: Armored Dinosaurs

Introduction

• Focus on the evolutionary history of Thyreophora, armored dinosaurs.
• Adaptations for carrying heavy loads, mainly seen in the pelvic girdle.

Early Thyreophorans

• Scutellosaurus

  • Early Jurassic bipedal form from North America.
  • Identified as a thyreophoran due to rows of bony scutes.
  • Lacked heavy weight adaptations.

• German Early Thyreophorans

  • Known from skull and scattered post-cranial remains.
  • Difficult to reconstruct due to limited bones available.

• Skeletosaurus

  • Early Jurassic form from Europe.
  • Complete skeleton available; debates on bipedal or quadrupedal nature.
  • Estimated length: 4 meters; weight: 600 pounds.

Trends in Dinosaur Evolution

• Early dinosaurs often small (1-2 meters), more generalized, bipedal, and omnivorous.

Diverse Thyreophoran Groups

• Stegosaurs

  • Found globally; earliest in Europe, North America, and China.
  • Characteristics: two rows of bony plates, spikes on tail, large size (8-9 meters, up to 6,800 pounds).
  • Huayangosaurus as an example with prominent spikes.

  Stegosaur Features

  • Plates possibly covered by keratin or skin.
  • Plates may serve defense, thermoregulation, or display purposes.
  • CT scans show elaborate blood vessels in plates.

  Stegosaur Adaptations

  • Loss of obturator prong for stronger pelvic girdle.
  • Early stegosaurs had spikes along backbone and shoulder spikes.
  • Later stegosaurs developed flat plates.
  • Stegosaurus features include a small brain, possibly a glycogen storage organ in sacral vertebrae.

• Ankylosaurs and Nodosaurids

  • Small, quadrupedal, heavily armored, similar to armadillos.
  • Ankylosaurs have rigid tails with bony club, notosaurids have flexible tails.
  • Ankylosaurs more ornate than nodosaurids.

Key Innovations

• Complete armor and spikes for additional weight.
• Pelvic girdle adaptations for weight bearing.
  • Simple rod-like ischium, reduced pubic bone.
  • Increased number of sacral vertebrae.
• Robust limbs designed for supporting weight, not speed.

Fossil Record

• Northern Hemisphere predominance, with Australian species known.
• Complete skeletons due to armor preservation, providing detailed skull feature analysis.
  • Excellent sense of smell and hearing in nodosaurids.

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These notes provide an overview of the key points discussed in the lecture about the evolutionary history and adaptations of the Thyreophora, focusing on stegosaurs and ankylosaurs.