Ol’ Fourlegs gets mapped
Could coelacanths be the transitional evolutionary species that links sea animals to land animals?
The East London Museum curates the most famous fish specimen in the world, the first coelacanth known to science.
This fish is the holotype – the specimen used as the basis for the original description of coelacanths by JLB Smith in 1939. Saved for science in 1938 by Marjorie Courtenay-Latimer, it was undoubtedly the zoological find of the 20th century.
Today, a question often asked is whether the coelacanth might be the transitional evolutionary species that links sea animals to land animals.
Scientists debated the question of Old Fourlegs (a nick-name given to the coelacanth by JLB Smith because of its four limb-like fins) being the ancestor of land vertebrates for many decades and an answer was finally published in April 2013 in the journal Nature.
Unravelling the DNA of the coelacanth indicates the lungfish as the closest relative to land animals and not the coelacanth. However, coelacanths are still important fish to study in understanding the transition of vertebrates from the sea to the land.
Coelacanths are more closely related to humans genetically than are ray-finned fish and sharks. The full genome (genetic material) of the coelacanth is almost 3 billion ‘letters’ of DNA (similar to the human genome). Studying the coelacanth offers clues to the genetic changes that reveal information about the evolution of tetrapods (animals having four limbs) – the line giving rise to amphibians, birds and mammals. The research paper confirms that genes which are necessary for limb formation are present in the fins of the coelacanth.
This work will also assist in understanding tetrapod evolution especially with regard olfaction, immunity, nitrogen excretion and the development of tail, eye, ear and brain.
Another interesting aspect of the work indicates ways to compare the coelacanth genome to the genomes of other vertebrate species, including other fish. Here it was discovered that the proteins which make up DNA in the coelacanth have changed very little over time.
One of the reasons for the slow evolution of coelacanth genes could be the lack of natural selection pressure, considering the stable marine environment in which these creatures live.
“The proteins which make up DNA in the coelacanth have changed very little over time.”
At ocean depths of between 90-120 meters and utilising underwater caves, coelacanth habitats have remained unchanged for millennia. Living coelacanths off the east coast of Africa and Indonesia have changed very little over millions of years and they are perfectly suited to the marine environments in which they feed and breed.
Researchers from 12 countries, representing 40 institutions, contributed to this study. Funding agencies included the African Coelacanth Ecosystem Programme and the SA Department of Science and Technology.
East London Museum Scientist