Proto-Chukotko-Kamchatkan is the hypothetical common ancestor of the Chukotko-Kamchatkan languages.

The Proto-Samic language is the hypothetical, reconstructed common ancestor of the Samic languages.

The hypothetical last common ancestor of archosaurs is thought to have shared many features with Erythrosuchus, many of which are found in the braincase.

It also bears similarity to the hypothetical ancestor of a group of parasitic worms, the Acanthocephala.

It is the hypothetical ancestor common to all Algonquian speech, 4,000 words that scholars have compiled from the surviving tongues and documentation of the extinct ones.

These branching off points represent a hypothetical ancestor (not an actual entity) which would have the combined traits of the lines above it.

This hypothetical ancestor might then provide clues about what to look for in an actual evolutionary ancestor.

The Urmetazoan is the hypothetical last common ancestor of all animals.

The hypothetical last common ancestor of all bilateria is termed the "Urbilaterian".

These three main lines of descent, Crick has noted, "seem a very long distance from their hypothetical common ancestor."