Evolutionary Aspects of the Animal Kingdom

General Concepts

  • Definition of animals

  • Characteristics of animals

  • Diversity of animal species

  • Origins of animals

  • Classification of animals

What is an Animal?

  • Common use: Refers to non-human animals

  • Biological definition: All members of kingdom Animalia (Metazoa)

  • Derived from Latin "animalis" meaning "having breath" or "having soul"

Characteristics of Animals

  • Multicellular eukaryotes without a cell wall

  • Heterotrophic in nutrition

  • Motile at some life stage

  • Reproduction: Asexual or sexual (mostly)

  • Possess nerve and muscle tissues in most species

Diversity of Animals

  • Over 1 million known species

  • Varied habitats and characteristics

Animal Origins

  • Kingdom Animalia is monophyletic (single common ancestry)

  • Evolved from a colonial flagellated protist around 700 mya

  • Evidence: Morphological and molecular similarities with choanoflagellates

Organization of the Animal Kingdom

  • Approximately 35 recognized phyla

  • Phyla grouped into clades based on shared characteristics

Evolutionary Aspects

  • Animals likely evolved from colonial unicellular ancestors in the Precambrian

  • Specialized cells and layered structures emerged over time

Comparison of Animal vs Plant Cells

  • Animals lack cell walls, have centrioles, lysosomes, and unique organelles like secretory vesicles

  • Tissue stability in animals provided via extracellular matrix and cell junctio