Aposolor
The aposolor evolved directly from the aposolis dragon ancestor. The aposolor stayed a water-dweller through almost all of its evolutionary stages and is the ancestor to all dragons with zero to two limbs. The aposolor’s tail split into two, which later on either fused into one again, or became limbs.
The majority of water-dwelling dragons come from the aposolor, though not all. Some of the aposolor’s descendants evolved to live on land, but compared to their water-dwelling relatives this number is very small.