 Fossilised bony fin rays show large elongated pectoral fins and a tall vertical tail fin.The gill arches were lined by gill rakers, equipped by a unique system of delicate bone plates, that filtered plankton from the sea water, the main food source.Along with its close pachycormid relatives "Bonnerichthys" and "Rhinconichthys", "Leedsichthys" is part of a lineage of large-sized filter-feeders that swam the Mesozoic seas for over 100 million years, from the middle Jurassic until the end of the Cretaceous period.