Today three early tetrapods are known and none has five digits.

The ZRS drives the early spatio-temporal expression pattern in the limb of tetrapods.

Lungfish are a unique order of sarcopterygian fish cleidographically positioned between tetrapods and fish.

The earliest tetrapods lived in lush, swampy environments that were not in risk of evaporating.

This feature is present in sharks and rays, and in extant relatives of tetrapods, the lungfishes.