A new Carboniferous coelacanth illuminates the evolution of the actinistian hyobranchial skeleton

Here we introduce a new genus and species, Aemilia stellata n. gen., n. sp., from the Late Carboniferous (Pennsylvanian) of Texas, United States. The use of micro-computed tomography (µCT) has revealed in exquisite detail the complete series of the hyoid and branchial arches as well as part of the braincase, dermal skull roof and cheek, and pectoral girdle. Our new data shed light on the organisation of the skull in coelacanths and allow us to identify new trends in the evolution of the neurocranium and hyobranchial skeleton.

A phylogenetic analysis of actinistian interrelationships reconstructs Aemilia stellata n. gen., n. sp. as the oldest representative of a large Mesozoic radiation of coelacanths, which extends its roots into the Carboniferous. Based on the new topology, coelacanth systematics are reviewed, and we propose a new phylogenetic definition of the order Coelacanthiformes. By its unexpected combination of features, Aemilia stellata n. gen., n. sp. bridges the gap between Devonian and post-Carboniferous coelacanths and reveals that the hyobranchial skeleton displays a certain degree of evolutionary plasticity in the traditionally considered “static” coelacanth anatomy.