Evolutionary Biology: Phylogenetics, Fish Classes, and Molecular Techniques

Diagrams that show the evolutionary lineages and relationships of different species over relative time.

Phylogenetic trees

The traditional method of constructing evolutionary trees by comparing sizes, shapes, and developmental structures of living organisms and fossils.

Morphological comparison

The superclass of jawed vertebrates that includes most fish and all tetrapods.

Gnathostoma

Animals that have a skull but are not classified as vertebrates because they lack a backbone; e.g., hagfish.

Craniates

The group of jawless, eel-like fish that have a skull but no backbone; includes hagfish.

Hyperotreti

The group of jawless, primitive vertebrates identified by a single nostril and sucker-like mouth; includes lamprey.

Hyperoartia

The class of fish with cartilaginous (rather than bony) skeletons, thick skin without true scales, and no swim bladder; includes sharks and rays.

Chondrichthyes

The class of bony fish characterized by bony skeletons, true scales, paired fins, and movable fin rays; the most diverse class of fish.

Osteichthyes

The subclass of lobe-finned fish that includes coelacanths, lungfish, and all tetrapods (amphibians, reptiles, birds, mammals).

Sarcopterygians

The subclass encompassing most modern ray-finned fish, including sturgeon, gar, and teleosts.

Actinopterygians

A group of ancient ray-finned fish considered relic bony fishes; they lack scales on most of the body and have a cartilaginous skeleton; e.g., sturgeon.

Chondrostei

Ancient ray-finned fish with bony scales and a mainly cartilaginous skeleton; e.g., gar.

Semionotiformes

The largest and most diverse group of bony fish, comprising the remainder of ray-finned fish; includes herring, carp, salmon, tuna, and pufferfish.

Teleosts

A living fossil once thought extinct alongside the dinosaurs, rediscovered alive in 1938; forms an important evolutionary link between fish and four-legged land animals.

Coelacanth

Four-limbed vertebrates; includes amphibians, reptiles, birds, and mammals — all descended from lobe-finned fish.

Tetrapods

The use of differences in protein and DNA sequences to determine evolutionary relationships between species.

Molecular phylogenetics

A gel electrophoresis technique used to separate proteins by size, which can be used qualitatively to compare muscle protein profiles across species.

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