Animal phylogeny

Animal phylogeny is the pattern of evolutionary relationships among animals, reconstructed from shared traits, fossils, and molecular evidence.

Phylogenetics: The study of evolutionary relationships among organisms using inherited characteristics. Animal phylogeny is one application of this broader method.
Phylogenetic tree: A branching diagram representing hypotheses about evolutionary relationships. Animal phylogeny is commonly presented as a tree of branching lineages.
Bilateria: The animal group whose members typically develop with bilateral symmetry and three primary tissue layers. This large branch contains most familiar animal diversity.
Coelomata: A proposed animal clade grouping arthropods with vertebrates based on a shared body cavity. Molecular evidence largely displaced this grouping in favor of Ecdysozoa and Lophotrochozoa.
Cladistics: A method of classifying organisms by shared derived traits and common ancestry. Its nested groups express hypotheses about animal ancestry.
Maximum likelihood: A statistical method that selects the model parameters most likely to produce observed data. It is widely used to estimate animal trees from molecular sequences.
Ecdysozoa: A group of animals that grow by shedding an external cuticle. Molecular evidence united arthropods and nematodes in this major animal clade.
Radiata: A historical grouping of radially symmetrical animals, especially cnidarians and ctenophores. Its apparent simplicity obscures uncertainty about early animal branching.
Homology: Similarity between biological features due to inheritance from a common ancestor. Homologous animal traits provide evidence of shared ancestry.
Bayesian phylogenetics: A framework for estimating evolutionary trees by combining data with prior probabilities. It quantifies uncertainty in competing hypotheses of animal relationships.

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