Modern Fish, Coelacanths, Tiktaalik, and Us

Tiktaalik roseae, illustration
An illustration of Tiktaalik roseae from Wikipedia. Credit: ArthurWeasley.

In the last several years, scientists have mapped in detail the lines of descent that resulted in aquatic vertebrates (fish) being able to survive and function outside water—including lines of descent that today have resulted in the mammals. Periodic discoveries stimulate interest in the media, such as the discovery last year of the 375-million-year-old Tiktaalik, or occasional sightings of coelacanths, an order of fish once thought to be long-extinct. But how are these animals related to each other and to us?

New Scientist published an article last week discussing new research into the coelacanth’s fins (specifically, when the difference between the coelacanth’s symmetric appendages and our asymetric appendages arose). But what I found especially interesting was a graphic demonstrating the relationships between extant lifeforms and notable extinct relatives, including when they are thought to have lived.

Diagram showing relationship between extant fish and tetrapods and extinct relatives.
See full-sized image. Source: New Scientist.

Perhaps this will help provide a framework when reading about these fascinating animals.