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.