Animal Evolution and Diversity

What is an animal? Heterotrophic eukaryote (must ingest food) No cell walls surrounding cells MOST have muscle cells and nerve cells MOST are diploid and reproduce sexually

The life cycle of a sea star Summary starting at adult: 1.Meiosis to make gametes 2.Gametes fuse to make zygote 3.Zygote becomes blastula 4.Blastula forms gastrula 5.Gastrula made of endo, ecto, and mesoderm 6.MOST animals develop into adult stage, some have larval stage first (sea star)

Homeoboxes Unique set of DNA sequences that regulates the development of all eukaryotes Hox genes are essential in embryonic development as they identify the various segments of the body

Animal Ancestors Oldest ancestor most likely resembled colonial protists Evolution hypothesis: Colonial aggregate of a few cells forms Larger colonies formed hollow spheres Cells become specialized for reproduction, locomotion, and feeding Layers developed Gastrula-like protoanimal may have evolved

Animal Ancestors (cont’d) The oldest known animal fossils date to about 575 million years ago The first animals must have developed prior to these fossils *The beginning of the Cambrian period, about 542 million years ago, shows a dramatic increase in animal diversity million years in the Cambrian explosion Evolution of hard body coverings allowed for increasing possibilities for predator-prey and defense interactions Increases in atmospheric oxygen allowed more efficient metabolism

Animal Body Plans Symmetry: radial symmetry: parts radiate from the center Ex: sea anemone bilateral symmetry: mirror-image right and left sides Ex: lobster anterior: head end posterior: tail end dorsal: back surface ventral: belly surface The symmetry of an animal fits its lifestyle Radial: observes all sides Bilateral: sense organs in head to facilitate mobility

Animal Body Plans Body cavity: Hydrostatic skeleton: noncompressible fluid in the body cavity Provides a rigid structure against which muscles contract, moving the animal True coelom: true body cavity Pseudocoelom: body cavity partially lined by mesoderm No body cavity (acoelomate): body solid except for the digestive sac

Animal Body Plans Gastrulation: Protostomes: gastrula opening becomes the mouth Deuterotomes: gastrula opening becomes the anus

Phylogenetic Tree using body plans