Some rough descriptions for the dragons of my world and kinda how they evolved
Draig
Medium sized scaly and winged lizards. They live in the jungle of Silca. They're omnivores and hunt small prey.
[Leviathan ancestor]
As Draigs spread across silca some of them wandered to the shore where they started hunting fish. Eventually this species evolved to be amphibious. They kept their wings but their feet adapted to swimming and hunting fish. Additionally they started growing longer tails. And weighed less.
Leviathan
The proto-leviathan has lost its wings for a third set of fins, additionally they have lost their ability to breathe on land. They have a long body and their tail developed a back fin. The leviathan evolved to be able to go deeper and deeper to find more prey. As the prey grew in size deeper down, the leviathans started growing bigger too.
Taniwha
As proto-leviathans started hunting for deeper prey they also pushed fish higher towards the surface. Those of the [leviathan ancestor]s that were good fliers began hunting fish close to the surface by swooping out of the air and into the water, grabbing them with their mouth and then resurfacing and flying off before repeating the whole thing.
Drekirm
Another group of draigs wandered into the mountains, due to the rough terrain and their sub optimal ability to climb the wings of these draigs grew to more easily traverse this area.
Raithon
Through hundreds of years they grew more and more comfortable in the air until they never came down again. Raithons have lost their legs and have gained large leathered and flexible wings. They always stay in the air, gliding on the harsh winds of the Silca mountains. They primarily hunt birds. They only land to lay eggs and take care of them. They wrap their long bodies around the egg. For more stable flight they evolved a tailfin of sorts.