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A Devonian digit-bearing vertebrate with eight anatomical digits in the forelimb, demonstrating that a five-digit condition was not universal in early limbs.

A cephalochordate lineage used in comparative analysis of chordate genomes. Modern amphioxus is a living relative, not the actual ancestor of vertebrates.

The second vertebra; its specialization varies across vertebrate lineages.

A member of the animal lineage characterized ancestrally by bilateral organization, including chordates and many other groups. bilaterian affinity does not imply vertebrate affinity.

A geological period beginning approximately 539 million years ago, with exceptional deposits documenting diverse early animals, including early vertebrates. Increased fossil visibility and biological diversification must be distinguished.

A member of the lancelet lineage. Its anatomy is informative for comparisons, but a living lancelet is not an unchanged ancestor of vertebrates.

A member of the lineage uniting living hagfish and lampreys. Jawlessness alone cannot assign an extinct vertebrate to this lineage.

A Silurian armoured jawed vertebrate with large marginal jaw bones previously associated with bony vertebrates.

A skull-roof bone formed by integration of frontal and parietal components, characteristic of frogs and some other vertebrates.

A member of an extinct armoured jawless lineage commonly placed on the gnathostome stem outside osteostracans and jawed vertebrates.

A ray-finned vertebrate whose skin expression of enamel-matrix genes contributes to comparisons of enamel and ganoine evolution.

A member of the jawed-vertebrate lineage. Crown usage includes the ancestor of living cartilaginous and bony vertebrates and all its descendants; a total-group usage additionally includes jawless stem relatives. The usage must be stated when discussing early fossils.

A jawless vertebrate with a strongly specialized feeding apparatus and slime-producing system. Soft-tissue anatomy and secondary modifications make the ordinary fossil record difficult to interpret.

A Chengjiang fossil animal important to interpretations of early vertebrate anatomy.

A member of the living human species. Our anatomy retains deeply inherited vertebrate organization alongside derived specializations.

An Early Devonian stem jawed vertebrate combining an extensively ossified dermal roof with informative braincase anatomy.

An Ediacaran animal interpreted as a mollusc-like bilaterian. It informs the timing of animal differentiation without being a proposed vertebrate ancestor.

An Early Devonian Siberian jawed vertebrate whose braincase–shoulder relationship supplies evidence for a posterior pharyngeal component of the pectoral girdle.

A jawless vertebrate lineage with a specialized oral apparatus. Living lamprey anatomy is informative without being a direct reconstruction of the ancestral vertebrate.

An Early Devonian Mongolian jawed vertebrate whose braincase contains a trabecular internal tissue interpreted as endochondral bone. Implications for ancestral bone depend on both tissue identity and phylogenetic placement.