Shedding light on the oldest oceanic reptiles: synchrotron microtomography of early ichthyosaur fossils from the Arctic

This study uses fossils of the geologically oldest-known pelagic marine reptiles to elucidate the adaptive evolution, timescale, and environmental context of the earliest tetrapod transition to life in the open sea. The remains include an articulated skull and tail-fin section representing at least two different earliest Triassic (~249 Ma) ichthyosaur taxa. These were discovered on Svalbard in the Scandinavian Arctic. The specimens are well-preserved but encased in hard limestone concretions that are difficult to prepare without damaging the fragile bones. The dense matrix also has crystalline calcite inclusions that are resistant to conventional micro-CT. High-resolution PPC-SR-micro-CT is therefore crucial to comprehensively analyse the osteology, functional morphology, and bone microstructure of these unique skeletal remnants. Such data will underpin accurate reconstructions of lifestyle and determine both the phylogenetic and palaeoecological implications of the first ichthyosaurs.