How to Draw a Phylogeny

Introduction

• Previous session: How to read a phylogeny.
• Focus of this session: How to draw a phylogeny from given relationships.
• Example used: Phylogeny of vertebrates.

Basic Statements and Terms

• Dimitrodon: A four-legged sail-backed predator, initially discovered in Canada but found widely, closely related to mammals.
• Synapsids: One of the lineages that evolved to live on land, includes Dimitrodon and humans.
• Diapsids: Another lineage including T-Rex, pigeons (birds), and crocodiles.
• Anapsids: Group historically used to describe reptiles like snakes and lizards. Not entirely accurate by modern understanding.

Drawing a Phylogenetic Tree

• Splits in Evolution:
  • Two major splits in land-dwelling vertebrate tetrapods: into synapsids and diapsids.
• Timeline:
  • Begins at the Carboniferous period, noted for coal deposits (Mississippian and Pennsylvanian).
  • Ends at the modern day (time = 0).
  • Important timelines: Permian period (250 million years ago) and Cretaceous-Paleogene boundary (66 million years ago).

Tree Components

• Lizards and Snakes: Modern representatives stretch from Carboniferous to today.
• Crocodiles and Dinosaurs: Belong to diapsids, dinosaurs further split into avian and non-avian.
• Us and Dimetrodon: Part of synapsids showing evolutionary relation to mammals.

Phylogenetic Concepts

• Clades: Groups including an ancestor and all its descendants.
  • Monophyletic: One branch, all descendants of a single ancestor.
  • Example: Diapsids as a clade including crocodiles, birds, dinosaurs.
• Paraphyletic: Includes an ancestor, but not all descendants.
  • Example: Non-avian dinosaurs excluding birds.
  • Example: Traditional definition of fish missing mammals and amphibians.
• Polyphyletic: Groups together different branches not sharing a common ancestor within the group.
  • Example: Early views of whales as fish.

Conclusion

• Importance of understanding phylogenetic terms and drawing accurate trees.
• Emphasis on using monophyletic groups in biological classification.
• Recognition of paraphyletic groups as less ideal, but sometimes necessary in understanding evolutionary transitions.

Key Terms

• Synapsids, Diapsids, Anapsids: Different evolutionary lineages.
• Monophyletic, Paraphyletic, Polyphyletic: Types of evolutionary groupings.
• Carboniferous, Permian, Cretaceous: Geological time periods relevant to vertebrate evolution.