Introduction to Animal Diversity
27.1 Features of the Animal Kingdom
The animal kingdom is very diverse, but animals share many common characteristics, such as methods of development and reproduction.
Complex Tissue Structure
Animals, besides Parazoa (sponges), are characterized by specialized tissues such as muscle, nerve, connective, and epithelial tissues.
Animal Reproduction and Development
Most animals undergo sexual reproduction and have similar forms of development dictated by Hox genes.
27.2 Features Used to Classify Animals
Animal Characterization Based on Body Symmetry
Animals can be classified by three types of body plan symmetry: radial symmetry, bilateral symmetry, and asymmetry.
Animal Characterization Based on Features of Embryologica...
Animals may be characterized by the presence of a coelom, formation of the mouth, and type of cell cleavage during embryonic development.
27.3 Animal Phylogeny
Constructing an Animal Phylogenetic Tree
Phylogenetic trees are constructed according to the evolutionary relationships that exist between organisms based on homologous traits.
Modern Advances in Phylogenetic Understanding Come from M...
The process of establishing relationships between organisms is increasingly becoming more accurate due to advances in molecular analysis.
27.4 The Evolutionary History of the Animal Kingdom
Pre-Cambrian Animal Life
Early animal life (Ediacaran biota) evolved from protists during the pre-Cambrian period, which is also known as the Ediacaran period.
The Cambrian Explosion of Animal Life
During the Cambrian period, the most rapid evolution of new animal species occurred, but the cause of this explosion is still unknown.
Post-Cambrian Evolution and Mass Extinctions
The post-Cambrian era was characterized by animal evolution and diversity where mass extinctions were followed by adaptive radiations.