Using X-ray microtomography, we describe the ossification events during the larval development of a non-teleost actinopterygian species: the Cuban gar Atractosteus tristoechus from the order Lepisosteiformes. We provide a detailed developmental series for each anatomical structure, covering a large sequence of mineralization events going from an early stage (13 days post-hatching, 21mm total length) to an almost fully ossified larval stage (118dph or 87mm in standard length). With this work, we expect to bring new developmental data to be used in further comparative studies with other lineages of bony vertebrates. We also hope that the on-line publication of these twelve successive 3D reconstructions, fully labelled and flagged, will be an educational tool for all students in comparative anatomy.