Vertebrate Cladistics

paraphyletic group

A group that includes a common ancestor and some but not all of its descendants.

polyphyletic group

A group that pulls together organisms that only share a distant common ancestor, without including all descendants.

monophyletic group

A group of species descended from a single common ancestor.

homoplasy

Similar traits that arise not from a common ancestor but due to convergent evolution.

cladistics

A method established by Willi Hennig for building evolutionary trees based on shared derived characteristics.

phenetics

A classification approach based on overall similarity of organisms.

matrix

A table constructed in cladistics where rows represent taxa and columns represent chosen characters.

parsimony

The principle that the simplest explanation, requiring the fewest evolutionary changes, is likely the correct one.

Cambrian Explosion

A rapid diversification of life forms approximately 540 million years ago, from which most animal phyla originated.

Porifera

A phylum of invertebrates commonly known as sponges, characterized by their porous bodies and lack of true tissues.

Cnidaria

A phylum that includes jellyfish and sea anemones, characterized by stinging cells called cnidocytes.

Nematoda

A phylum encompassing roundworms, having complete digestive tracts and diverse life forms.

Annelida

A phylum of segmented worms known for their bilateral symmetry, closed circulatory system, and segmentation.

Mollusca

A diverse group of soft-bodied invertebrates, including snails and squids, characterized by their mantle and radula.

Arthropoda

The most diverse group of animals, including insects and crustaceans, characterized by jointed appendages and exoskeletons.

Echinodermata

A phylum of deuterostome invertebrates, such as sea stars and sea urchins, known for their radial symmetry and water vascular system.