In-Depth Notes on the Origin and Evolution of Dinosaurs

ORIGIN OF DINOSAURS

• Artwork Reference: Brusatte et al. 2010

LEARNING GOALS

• Phylogenetic Tree Interpretation: Understand the evolutionary relationships of dinosaurs.
• Recognition of Groups: Identify groups and key innovations leading to the origin of dinosaurs.
• Skull Morphology Differences: Distinguish between synapsid, diapsid, and anapsid skulls.
• Features Uniting Dinosaurs: Identify features that distinguish dinosaurs from other Archosaurs.
• Geological Timeline: Identify when and where the earliest dinosaurs appeared.

EVOLUTION OF DINOSAURS

• Taxonomy Breakdown:
  • Kingdom: Animalia
  • Phylum: Chordata
  • Sub-phylum: Vertebrata
  • Class: Dinosauria
  • Order: Saurischia
  • Sub-order: Theropoda
  • Family: Tyrannosauridae
  • Genus: Tyrannosaurus
  • Species: Tyrannosaurus rex

CHORDATES AND THEIR ANCESTRAL SIGNIFICANCE

• Key Features:
  • Evolved around 500 million years ago; developed the notochord and gill slits.
  • Example organism: Pikaia (found 510 million years ago in Cambrian, British Columbia).

ORIGIN OF TETRAPODS: SUBPHYLUM VERTEBRATA

• Vertebrate Features:
  • Calcified internal skeleton, true jaws, and a major evolutionary split leading to fleshy lobe-finned fish.

TIKTAALIK (Transitional Fossil)

• Age: Approximately 375 million years ago.
• Characteristics:
  • Features: Scales, fins, gills, neck and shoulder bones, ribs, and an elevated position for eyes (similar to crocodilians).

TETRAPOD CHARACTERISTICS

• Definition: Four-legged vertebrates including amphibians, mammals, and their common ancestors.
• Timeframe: First amphibians appeared around 360 million years ago.
• Features: Complex teeth and adaptations for both aquatic and terrestrial life.

TETRAPOD SKELETON FEATURES

• Common Structures:
  1. Four limbs
  2. Vertebral column (spine)
  3. Girdles (scapula for forelimb; ilium, pubis, ischium for back limb)
  4. Head with a skull and mandible
  5. Tail

ORIGIN OF AMNIOTES

• Definition: Class of tetrapods that include birds and mammals, unified by the amniotic egg.
• Significant Feature: Ability to lay eggs on land due to hard or leathery shells, minimizing dependence on water.

CLASSIFICATION OF AMNIOTES

• Skull Structure Analysis:
  • Anapsids: No openings in skull
  • Synapsids: One lower opening
  • Diapsids: Two openings

DIVERSIFICATION OF ARCHOSAURS

• Evolved in the Triassic with innovations like socketed teeth and antorbital fenestrae.
• Categories:
  1. Crocodilians: Mid-Triassic to present.
  2. Pterosaurs: Late Triassic to end of Cretaceous.
  3. Dinosaurs: Late Triassic to end of Cretaceous.
  4. Birds: Originating during the Jurassic period.

DISTINCTIVE FEATURES OF DINOSAURS

• Anatomical Characteristics:
  • Larger jaw muscle attachments for powerful biting.
  • Stronger forelimbs and unique mesotarsal joint facilitating upright movement (perforate acetabulum).

DINOSAUR CLASSIFICATION

• Saurischians vs. Ornithischians:
  • Saurischians: Spread pubis and ischium; variable teeth placement.
  • Ornithischians: Close-set pubis and ischium; often exhibit reduced front teeth with developed biting plates.

EARLY DINOSAURS

• Age: Earliest classified fossils appeared approximately 229 million years ago (Late TRIASSIC).
• Bipedal Evolution: Primarily bipedal ancestors that eventually led to re-evolution in quadrupedal forms.

FOSSIL EXAMPLES AND TIMEFRAME

• Triassic Dinosaurs: Compsognathus, Staurikosaurus, Plateosaurus, and Herrerasaurus.
• Late Cretaceous Examples: Triceratops, Tyrannosaurus rex, and Velociraptor.

CONCLUSION

• Next Topic: Effective understanding of theropods and their evolutionary implications will enhance knowledge of dinosaur evolution.