Scientists Find a Possible New Link in the Evolution of Tetrapods in the Ancient Coelacanth

Yesterday, Nature science journal published counterintuitive findings; when a fish's genes were transplanted into mice, the mice did not grow fins or scales but instead grew forelimbs and hind limbs. The DNA was extracted from an archaic fish of coelacanth origins, whose extinction has been traced back to the dinosaurs' period of demise. More specifically, scientists had successfully decrypted the genome of the African coelacanth. Ironically, present-day fish from the coelacanth lineage have only evolved negligibly when anatomical features are compared with the 300 million year old fossil record. That being said, both the coelacanth fish of yesteryear and the present possess appendages that are uncannily similar to the limbs of tetrapods called "lobed" fins.

 Many science aficionados wrongly use Charles Darwin's term of "living fossil" when speaking of coelacanth. Although there are extinct versions of the fish, coelacanths are living organisms that still thrive today. According to comparative biologist and co-author of the study, Kerstin Lindblad-Toh, coelacanths "live far down in the ocean, where life is pretty stable", and therefore "We can hypothesize that there has been very little reason to change."

Though extinct members of lung fish are more analogous to tetrapods than are coelacanth, based off of yesterday's genome analysis, the latter fish is a key informant regarding the evolution of marine-animals to land breeding animals. Obviously, anatomical analysis, such as the similarities in joints an bones that can be detected in both lobed fins and tetrapod limbs, can only reveal so much information. For this reason, the decoding of African coelacanth's genome is a feat. By understanding what genes are turned "off" and/or "on" when combined with external stimuli, as exemplified by interaction between the coelacanth's DNA and the host's, or mice's molecular biology, scientists can better determine how exactly coelacanth's started to share features of land animals.

The study primarily reveals a regulatory gene sequence that aids in stimulating the evolution of limbs. Despite this common thread between coelacanths and all 4-limbed animals today, the coelacanth retains a unique biological trait that helps to retain its ancient-like existence. This trait is immunity: Coelacanths lack immunoglobin-M, a protein possesses by almost every living organism. Instead, coelacanths possess 2 proteins that are distantly related to the aforementioned protein that is essential for vitality. Scientists believe that these 2 proteins somehow compensate for the missing immunoglobin-M. As with everything regarding coelacanths, they are an exception to the modern world we live in.