Keasius species were specialized planktivores that employed a filter-feeding mechanism analogous to that of the modern
basking shark Cetorhinus maximus. Fossilized gill rakers, teeth, and vertebral centra reveal a passive filtration system, where individuals swam with their mouths agape to draw in water via ram ventilation, straining zooplankton and small nektonic organisms from the water column. The close spacing and reduced size of teeth in preserved dentition further supported retention of minute prey particles while expelling excess water through the gills, as evidenced by specimens from
Oligocene deposits in Germany. ==References==