Lecture Notes: Introduction to Animal Diversity

Overview

• Focus on history of life on Earth as it pertains to animals
• No need to memorize specific timelines, focus on key evolutionary events

Pre-Cambrian and Ediacaran Period

• Ediacaran Period: Emergence of Ediacaran biota
  • First evidence of animal diversity in the fossil record
  • Weird, plant-like animals with no modern descendants
  • Marine life only

Cambrian Period

• Cambrian Explosion: Major diversification of animal life
  • Introduction of ancestors to modern invertebrates
  • Still marine
  • Possible causes: increased O2, protective ozone, increased oceanic calcium

Paleozoic Era

• Evolution of land plants before animals
• First land animals: ancestors of spiders and centipedes
• Introduction of marine and land vertebrates (e.g., Dimetrodon)
• Permian Period: Proto-mammals, not dinosaurs

Permian-Triassic Extinction Event

• Largest extinction event
  • 81% of marine species, 70% of terrestrial vertebrates lost
  • Possible causes: meteor impacts, volcanic eruptions, methane release
  • Ecological niches left empty, leading to the rise of reptiles

Mesozoic Era

• Rise of Dinosaurs and Reptiles: Dominance after extinction events
  • Dinosaurs, marine and flying reptiles
  • Birds and mammals evolve in the background

Cretaceous-Paleogene Extinction Event

• Meteor impact led to extinction of non-avian dinosaurs
  • Birds and mammals rise to dominance

Cenozoic Era

• Current Era: Dominance of mammals and birds
• Pattern: Mass extinctions -> empty niches -> evolutionary radiation

Introduction to Animal Groups

• Transition to focusing on specific animal groups
• Kingdom Animalia, also known as Metazoans

Phylum Porifera (Sponges)

• Simplest animals, lack tissues
• Body Structure: Supported by spongin and/or spicules
• Reproduction: Sexual (hermaphroditic) and asexual (budding or fragmentation)
• Feeding: Filter feeders using choanocytes

Sub-kingdom Eumetazoa

• Animals with true tissues
• Phylum Cnidaria (e.g., sea jellies, corals, anemones)
  • Body Plan: Diploblastic, radial symmetry
  • Digestive System: Incomplete, with gastrovascular cavity
  • Life Cycle: Polyp (sessile) and medusa (motile) forms

Class Anthozoa

• Includes sea anemones and corals
• Only polyp form
• Symbiotic relationships with dinoflagellate algae

Class Scyphozoa

• Known as jellyfish or sea jellies
• Typically medusa form, some are dimorphic

Summary

• Ecological patterns of extinction and radiation
• Introduction to different animal groups and their characteristics
• Continued exploration of animal diversity in future lectures