A Late Devonian coelacanth reconfigures actinistian phylogeny, disparity, and evolutionary dynamics
Alice M. Clement, Richard Cloutier, Michael S. Y. Lee, Benedict King, Olivia Vanhaesebroucke, Corey J. A. Bradshaw, Hugo Dutel, Kate Trinajstic, John A. Long
Abstract
The living coelacanth Latimeria (Sarcopterygii: Actinistia) is an iconic, so-called ‘living fossil’ within one of the most apparently morphologically conservative vertebrate groups. We describe a new, 3-D preserved coelacanth from the Late Devonian Gogo Formation in Western Australia. We assemble a comprehensive analysis of the group to assess the phylogeny, evolutionary rates, and morphological disparity of all coelacanths. We reveal a major shift in morphological disparity between Devonian and post-Devonian coelacanths. The newly described fossil fish fills a critical transitional stage in coelacanth disparity and evolution. Since the mid-Cretaceous, discrete character changes (representing major morphological innovations) have essentially ceased, while meristic and continuous characters have continued to evolve within coelacanths. Considering a range of putative environmental drivers, tectonic activity best explains variation in the rates of coelacanth evolution. Coelacanths are known for their conservative morphology. Here, the authors describe a 380 million year-old coelacanth fossil from the Gogo Formation (Western Australia) with morphology representative of a key transition where coelacanth morphology disparity shifts.