Question

WHAT IF? Imagine that we could replay the history of life. Is it possible that a group of vertebrates that colonized land could have arisen from aquatic gnathostomes other than the lobe-fins? Explain.

Short answer

Yes, other than the lobe-fins, a group of land-dwelling vertebrates could have originated from aquatic gnathostomes.

Step-by-step solution

Group of vertebrates

Living vertebrates possess a collection of derived characteristics that differentiate them from other chordates.

For example, due to gene duplication, vertebrates contain two or more types of Hox genes (lancelets and tunicates have only one). Several critical sets of genes that produce transcription factors and signaling molecules are also replicated in vertebrates.

Vertebrates arise from the lobe-fins

The third living lineage of lobe-fins is significantly more diversified than the coelacanths or lungfishes. These organisms evolved to land life during the mid-Devonian period. It led directly to vertebrates with limbs and feet, known as humans, part of the tetrapod lineage.

Vertebrates from aquatic gnathostomes 

Yes, vertebrates arise from the aquatic gnathostomes. The group of vertebrates that developed the paired appendages of aquatic gnathostomes could have provided a starting point for the development of limbs.

The colonization of dry land by marine or freshwater gnathostomes other than lobe-fins may have been aided by lineages that developed lungs, as those organisms would have been able to breathe air.