The coelacanth is a textbook example of what's sometimes termed a "living fossil." It belongs to a group called lobe-finned fishes, which were very common back in the Devonian. In its relatives, the long, lobed fins evolved into the four limbs of the tetrapods, which include us mammals. The lineage was thought to have died out millions of years ago, until African fishermen pulled up a coelacanth in the 1930s. Since then, a stable population has been found near the Cormoros, a set of islands that lie in between Madagascar and the African coast.

Since that time, a steady stream of the fish has been discovered along the African coast. Initial genetic testing indicated that these animals were very similar to the ones found in the Cormoros; this suggested that they had simply drifted to Africa on one of the prevailing currents in the area. But over time, sightings piled up over thousands of kilometers, ranging from Kenya south to South Africa. So a group of researchers went back and revisited the genetic data by sequencing the entire mitochondrial genome for 23 of the fish.

In contrast to the earlier results, the coelacanths off Kenya, Tanzania, and Mozambique contained some sequences that were unique to that population; the frequency of many alleles was also very different in the Cormoros population. Combined with videos that show coelocanths feeding normally off the African coast (including some apparently fertile females), and the authors conclude that there's probably a stable breeding population there.

Estimates of the genetic distance among these populations are very broad—the sequences are compared using a different species in the Pacific for comparison, and estimates of that speciation range from 5-30 million years. Still, even the low-end estimates suggest that the African coastal populations split off from the Cormoros group over 200,000 years ago. For context, polar bears are thought to have evolved from brown bears in less time than that.

It appears now that this living fossil has successfully colonized the African coast. Unfortunately, the area it has colonized is now subject to overfishing, which the authors say puts this new population at risk.

PNAS, 2011. DOI: 10.1073/pnas.1115675108 (About DOIs).