Living Dino-Fish
Table of Contents
The coelacanth (“see-la-kanth”) was found to be ‘alive and well’ in 1938 after millions of years of hiding, but is he really a ‘living fossil’?
Coelacanths spend most of their time in deep water (100-300m) eating squids and the like, which they find using their ‘electric sense’. When times get hard they sink into deeper water and ‘hibernate’. Coelacanths rarely move into shallow waters and therefore not many have been seen by scientists (about 200 individual fish so far). Local fishermen have probably caught and eaten far more, or simply thrown them away since they are said to taste horrible!. It is thought that there are very few of either species alive today (maybe only 1000), so we could easily ‘lose’ them if deep-water trawling continues unchecked.
The genus Latimeria (the coelacanths) has only two known living representatives. These are Latimeria chalumnae and Latimeria menadoensis . They both live in deep water (one off the coast of Africa and the other in Indonesian waters). The two species diverged a long time ago, maybe as much as 40M years, and their ancestors are known from the fossil record for as far back as 400M.
Discovery of the coelacanth
Coelacanths were believed to have gone extinct more than 80 million years ago (Mya) until the sensational rediscovery of one surviving member of this lineage, Latimeria chalumnae, in 1938. Since then, more than 200 coelacanths have been caught off the Comoro archipelago near the eastern coast of Africa in the Indian Ocean (Forey, 1998).
Discovery of the Indonesian coelacanth
The discovery of the second species of coelacanth off the coast of Sulawesi, Indonesia, in 1997 surprised the scientific community. The extensive interviews with Indonesian fishermen, combined with the vast distance from the Comoro archipelago, supported the idea that the Indonesian coelacanths are part of an established north Sulawesi population, and not simply waifs from the Comoran population (Forey et al., 1998).
However, taxonomic confusion raised by overlapping morphological variations has posed problems in relation to coelacanth dispersal and biogeography. The Indonesian coelacanth is morphologically similar to the Comoran coelacanth (Erdman et al. 1999). Only one important morphological character is that of scale ornamentation (Holder et al., 1999).
Divergence time between the two coelacanths
We estimated the divergence time between the two species of coelacanths based on the whole mitochondrial genome sequences using the Bayesian approach (see Divergence Time Estimation). The estimated divergence time between two coelacanths fell in the range of 40-30 Mya. This age was much older than those of the previous molecular studies (< 6.3 Mya).
But are they really ‘living fossils’?
I would argue that every creature alive today is equally ‘modern’. The coelacanth developed his body-form a long time ago, but surely he has been evolving ever since – just like the rest of us? There are no known fossils of the two living species, and all we have is their relatives. It is true that their closest relative disappeared from the fossil record about 70M years ago, before the dinosaurs were even thought about, and that other very close relatives of the coelacanth ‘came ashore’ about 360M years ago, and are possibly our ancestors. But does that mean that the coelacanths are our ancestors? The answer, to my mind, is a resounding no. Nothing alive today could possibly be our ancestors and while it is true that their ancestors were also ours, you could say that for any living thing if you go back far enough!
Modern coelacanths do resemble us in a few ways. They are big, about as long as we are tall – and about the same weight. They can live for about 60 years, and only become sexually mature at 20. Each one has unique markings, and they are recognizable as ‘individuals’. Coelacanth fins look like primitive legs (hence ‘old four-legs’), and they have the remains of an early ‘lung’. But they live in another world!