 The largest trilobites may have been 45 centimetres long and weighed 4.5 kilograms.Trilobites made a sudden appearance in the fossil record.There appears to be a considerable evolutionary gap from possible earlier precursors such as "Spriggina", which is found in the 550 million year old Ediacaran-age rocks of Australia, and thus predates trilobites by some 30 million years.