Why coelacanths are not 'living fossils': a review of molecular and morphological data.

A series of recent studies on extant coelacanths has emphasised the slow rate of molecular and morphological evolution in these species. These studies were based on the assumption that a coelacanth is a 'living fossil' that has shown little morphological change since the Devonian, and they proposed a causal link between low molecular evolutionary rate and morphological stasis. Here, we have examined the available molecular and morphological data and show that: (i) low intra-specific molecular diversity does not imply low mutation rate, (ii) studies not showing low substitution rates in coelacanth are often neglected, (iii) the morphological stability of coelacanths is not supported by paleontological evidence. We recall that intra-species levels of molecular diversity, inter-species genome divergence rates and morphological divergence rates are under different constraints and they are not necessarily correlated. Finally, we emphasise that concepts such as 'living fossil', 'basal lineage', or 'primitive extant species' do not make sense from a tree-thinking perspective.

Casane D ，Laurenti P 《-》

A Late Devonian coelacanth reconfigures actinistian phylogeny, disparity, and evolutionary dynamics.

Clement AM ，Cloutier R ，Lee MSY ，King B ，Vanhaesebroucke O ，Bradshaw CJA ，Dutel H ，Trinajstic K ，Long JA ... -  《Nature Communications》

Extremely slow rate of evolution in the HOX cluster revealed by comparison between Tanzanian and Indonesian coelacanths.

Coelacanths are known as "living fossils" because their morphology has changed very little from that in the fossil record. To elucidate why coelacanths have evolved so slowly is thus of primary importance in evolutionary biology. In the present study, we determined the entire sequence of the HOX cluster of the Tanzanian coelacanth (Latimeria chalumnae) and compared it with that of the Indonesian coelacanth (L. menadoensis), which was available in the literature. The most intriguing result was the extremely small genetic divergence between the two coelacanths. The synonymous divergence of the HOX coding region between the two coelacanths was estimated to be 0.07%, which is ~11-fold smaller than that of human-chimp. When we applied the estimated divergence time of the two coelacanths of 6 million years ago (MYA) and 30 MYA, which were proposed in independent mitochondrial DNA analyses, the synonymous substitution rate of the coelacanth HOX cluster was estimated to be ~11-fold and 56-fold smaller than that of human-chimp, respectively. Thus, the present study implies that the reduction of the nucleotide substitution rate in coelacanth HOX genes may account for the conservation of coelacanth morphology during evolution.

Higasa K ，Nikaido M ，Saito TL ，Yoshimura J ，Suzuki Y ，Suzuki H ，Nishihara H ，Aibara M ，Ngatunga BP ，Kalombo HW ，Sugano S ，Morishita S ，Okada N ... -  《-》

Interspecies insertion polymorphism analysis reveals recent activity of transposable elements in extant coelacanths.

Naville M ，Chalopin D ，Volff JN 《PLoS One》

Oldest coelacanth, from the Early Devonian of Australia.

Johanson Z ，Long JA ，Talent JA ，Janvier P ，Warren JW ... -  《-》