Last week science writer Carl Zimmer moderated a cross-disciplinary discussion on the newly sequenced genome of the elusive coelacanth (pronounced ‘seel-i-kanth’).
This deepwater, lobe-finned fish was one of the most surprising discoveries of the 20th century and a key component of our evolutionary past. The coelacanth is sometimes colloquially referred to as a “living fossil”, a situation in which fossils of an animal are found before the living counterpart. Presumed extinct for 70 million years, it was found flopping around in trawler nets off the coast of Africa in 1938. Today there are only two extant species of coelacanth, and they are among the most critically endangered species on the planet.
This enigmatic fish is actually one of the more useful launching pads for explaining evolutionary theory. At the first, it shows how critical a role environment plays in the formula of natural selection. The fossil record indicates that coelacanths could once be found in abundance, densely hugging the littoral regions of Africa and south Asia. It was then believed to have gone extinct at the time of the impact event marked by the Cretaceous-Paleogene (K-Pg) line. Its later “re-discovery” tells us that certain species of the fish were able to survive in narrow pockets of their environment where selection pressures operated at lower frequencies.
The sweeping influences on climate rained down by the K-Pg impact were not uniform across all coelacanth habitats, and those that survived were nudged, genetically and morphologically, in some rather interesting directions. The modern coelacanth is in fact quite distinct from its ancestral brethren. In the image below, a profile view of the Latimeria and its closest fossil relative, you can see a number of skeletal differences among the fins, main body and vertebrae.
The coelacanth is also one of the more elegant examples of a transitional form. It’s believed to be one of the main species linking up gill-bearing, finned fish to air-breathing, limbed amphibians. Its unique fin structure, auditory system and vestigial lung are all precursory to the Devonian divergence of the tetrapods, and in fact the modern coelacanth shares more in common with these orders of organisms than with other modern fish.
Today this distant relative, which has an average lifespan of 60 years and can grow as large as 6.5 ft. (2 m) in length, can only be found along the coasts of the Indian Ocean and Indonesia. Learn more below.
Feature image courtesy of Todd Huffman