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Ornithiscians II: Frilly, Crested, and Ready to Rock

ORNITHISCHIANS II: FRILLY, CRESTED AND READY TO ROCK

Learning Goals

  • Pachycephalosaurs: Evaluate the possible functions of domes.

  • Ceratopsians: Evaluate the functions of frills and horns.

  • Marginocephalia: Describe features that unite and distinguish Pachycephalosaurs and Ceratopsians.

  • Ornithopods: Distinguish between major groups and discuss jaw and tooth adaptations related to feeding.

  • Hadrosaurs: Describe hypotheses regarding cranial crests related to sexual selection and communication.

Marginocephalians Overview

  • Two main groups: Ceratopsia and Pachycephalosauria.

  • Key features include thick skulls adapted for impact, generally used for either defense or display.

  • Pachycephalosaurs are referred to as "thick-headed reptiles" with distinct, dense skull roofs.

  • In stegosaurids, scutes varied in shapes and sizes, suggesting differentiation between species and potential sexual dimorphism

  • Designed for high-impact injuries; have skulls that can withstand such events.

  • High muscles in neck and brain orientation away from impact help in "head-banging" behaviors.

  • Sexual dimorphism may suggest some features were for display purposes.

    • Evidence from species such as Pachycephalosaurus wyomingensis, where skull structure varies with age.

Feeding Mechanisms

  • Pachycephalosaurs have leaf-shaped teeth, similar to those of thyreophorans, suggesting herbivorous diets with adaptations for fermentation.

Ceratopsia Overview

  • Also known as Horned Faces, characterized by beaks and a significant development of frills and horns.

  • Variability in group sizes with North American ceratopsids being larger and often more horned compared to their Asian counterparts.

  • Unique skull features, including post- and anti-orbital horns, evolved over time.

Basal Ceratopsians Characteristics

  • Examples include Psittacosaurus, which is bipedal with a hooked beak.

  • Development of a more massive skull with varying frill sizes in Protoceratops; possible functions include defense, display, and thermoregulation.

Evolutionary Progression

  • Early ceratopsians evolved in Asia, later dispersing to North America and diversifying significantly during the Late Cretaceous.

  • Development of post-orbital horns and larger frills correlated with a significant increase in body size and dental adaptation functions.

Ornithopod Characteristics

  • Ornithopods, often referred to as "bird feet", showcase significant diversity and successful adaptation across continents and climates.

  • Key features: stiff tails, broad beaks, and specialized dental batteries.

  • Derived variations show quadrupedalism for rapid movement.

Diets and Feeding in Ornithopods

  • Generally herbivorous with diverse diets including berries and angiosperms.

  • Anatomical adaptations allow for efficient chewing and mastication, critical for processing varied plant materials.

Hadrosaur Crests

  • Significant diversity in cranial crests primarily associated with sexual selection and communication.

  • Possible correlation with color variations and other display features.

Conclusion

  • Ornithischians demonstrate remarkable adaptability and evolutionary features that span across physical characteristics and behaviors for survival in the diverse habitats they occupied throughout the Cretaceous period.