One of the earliest vertebrates is Sacabambaspis, which was from the Middle Ordovician. Sacabambaspis is an extinct species of jawless fishes (called agnathans) and resembles extant cyclostomes, hagfishes and lampreys. Although cyclostomes are specialized agnathans for parasitism, they have some features of the earliest vertebrates. Today, the origins of limbs are considered as paired fins. Sacabambaspis and cyclostomes do not have paired fins , but they posses median fins (caudal fins).