A fiftieth anniversary reflection on the living coelacanth, Latimeria chalumnae: some new interpretations of its natural history and conservation status

Abstract

SynopsisIt all started about 400 million years ago, when representatives of a group of fish-like fleshy-finned creatures appeared in the fossil record (or was it through a childhood dream shared by all of us that we would one day study the coelacanth?). Many of the coelacanth's characters placed them close to the ancestry of terrestrial vertebrates. About 70 million years ago they disappeared from the fossil record. The discovery in 1938 of the first living coelacanth, in 1952 of the second and until now over 200 specimens parallels in excitement an encounter with a live dinosaur on a weekend walk, and in significance even more than that. For this year's 50th anniversary of the famous discovery of the first living coelacanth, we retraced the routes and visited the main actors of this zoological drama. New insights into coelacanth natural history were facilitated by novel interpretation of earlier data and our expeditions to the Comoro Islands, retracing the route of the second specimen, measuring unrecorded specimens, interviewing fishermen and describing their fishing crafts, and taking part in recent events on land and water near the only known habitat of the living coelacanth. Entry into this habitat and observations from the research submersible GE0 opened up a new era in coelacanth research. Past studies of preserved specimens, which were caught as an incidental bycatch, were supplemented for the first time by studies of free-living coelacanths in their natural habitat. The first film footage taken from the submersible revealed the entirely unfishlike movements of this creature. Its mode of locomotion is a combination of flying and gliding, interspersed with head stands and belly-up drifts which appear to defy gravity. The narrow range of habitat in which the coelacanth has been encountered has led us to realize how vulnerable this ancient relict is. The members of our expeditions therefore cooperated in establishing an international organisation to coordinate efforts to conserve the coelacanth.

Patterns, trends, and rates of evolution within the Actinistia

“…Our idea of Latimeria chalumnae as a 'living-fossil' has to take into account that evolutionary modifications (or sequential historical constraints) have occurred through time (ca. 380 My), and that L. chalumnae is not a primitive actinistian (e.g., Balon et al 1988, Balon 1991.…”

“…ineau 1987, Schultze 1987, Balon et al 1988. Simpson (1944) pointed out that the actinistians were a classic example of a taxon exhibiting 'low-rate' of evolution.…”

Observations on locomotion and feeding of released coelacanths, Latimeria chalumnae

“…One point immediately became apparent; the coelacanth is a very slow swimmer, as its ancestor probably was some 350 million years ago; it had changed its hydrodynamic structures little since the Palaeozoic (e.g. Balon et al 1988). Initially, the fish swam extremely slowly but, as it descended (to around 50 m), its speed very gradually increased and, although still moving relatively slowly, it appeared generally more active.…”

Complete HOX cluster characterization of the coelacanth provides further evidence for slow evolution of its genome

“…Indeed, the living coelacanth, Latimeria, is considered an evolutionary relict that has generated a great deal of intrigue since its discovery in 1938, with interests in its anatomy, physiology, ecology, interrelationships, and even politics (1). Because of its protected status, the best practical approach to its study is from the inside out, i.e., through comparative genomics.…”