Arandaspis prehistoric fish, artwork. This extinct aquatic vertebrate lived in the Ordovician period, about 500 million years ago. Arandaspis was a precursor to true bony fish. It had a streamlined body, reaching 5 centimetres in length, which was covered with knobbly scales. Hard bony plates covered the entire head, with openings for eyes, mouth and gills. Arandaspis lacked a jaw and was thought to feed by sucking in food particles from the bottom of the sea floor.