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A vertebrate belonging to the lineage of four-limbed vertebrates, including descendants whose limbs were reduced or lost.

A finned Devonian relative of digit-bearing vertebrates. Its pectoral skeleton combines retained fin rays with jointed internal structures relevant to limb evolution.

A Silurian jawless vertebrate preserving continuous paired ventrolateral fins, interpreted as a precursor to more localized paired appendages.

A member of the chordate lineage that molecular evidence places closer to vertebrates than are living cephalochordates.^[ref]

The hypothesis that two early large-scale duplication rounds contributed to the multiple paralogous genomic regions of jawed vertebrates. Hox clusters are one informative set of loci; a single family does not by itself establish genome-wide duplication.