Lecture on Evolutionary Biology and Phylogenetic Trees

Understanding Characters in Phylogenetic Trees

• Characters in biological context refer to traits used to infer evolutionary relationships.
• Biologists use evidence to argue where groups fall on a phylogenetic tree.

Synapsids and Their Fused Skull

• Synapsids: Characterized by a fused skull with fewer holes compared to dinosaurs.
  • Example: Dimetrodon has a skull more like mammals, with parts fused together.
  • Fused skulls provide protection but complicate muscle attachment.

Importance of Skull Muscles

• Skull muscles are crucial for jaw movement and chewing in vertebrates.
• Different evolutionary solutions for muscle attachment:
  • Synapsids: Closed skulls with external muscle attachment.
  • Dinosaurs: Openings in the skull for muscle passage.

Evolutionary Traits

• Apomorphy: A derived trait that signifies a change from an ancestral condition.
  • Synapomorphy: A shared derived trait that unites a group (e.g., fused skull in synapsids).
  • Autapomorphy: A unique trait found in a single lineage (e.g., human leg structure).

Ancestral Conditions and Derived Traits

• Plesiomorphy: Primitive or ancestral trait, not used to define evolutionary relationships.
  • Example: Whales have vestigial leg bones, a plesiomorphic trait.
  • Homoplasy: Convergent evolution where similar traits evolve independently (e.g., whales and fish).

Homology vs. Homoplasy

• Homology: Traits shared due to common ancestry, crucial for understanding evolutionary relationships.
• Identifying homologies helps differentiate from homoplasies and plesiomorphies.

Defining Dinosaur Characteristics

• Acetabular Foramen: A hole in the hip, defines dinosaurs.
  • Earliest dinosaurs were bipedal; quadrupedalism seen in some dinosaurs developed secondarily.

Evolutionary Dynamics

• Evolution is continuous; traits can be gained or lost over time.
• Birds, for example, may lose traits like the acetabular foramen over evolutionary time.

Future Topics

• Discussion on where turtles fit in the evolutionary tree.
• Review of key concepts: Synapomorphies, homology, and paraphyly.

These notes summarize key points from a lecture on evolutionary biology, focusing on characters and traits in phylogenetic trees, with specific examples from synapsids and dinosaurs.