So, I'm building this world where most of the lifeforms, for one reason or another, are reptiles. Now, I know there have been reptile dominant periods in Earth's history, so it isn't impossible for the modern ecosystem of another planet to be predominantly reptiles as well. I am working on the aquatic niches right now and I'm wondering, is it possible for a reptile to be amphibious? Or would an amphibious reptile just be an amphibian? To make things clear, here is what I am proposing for the life cycle of an amphibious reptile:
So, their larvae look kind of like salamander larvae except for one thing, scales growing from the smooth skin(which is partly why I made them have external gills instead of the internal gills that fish have). As they grow, they look more and more like an aquatic lizard than a salamander because of the scale growth. As for their habitat, they live in ponds and lakes. They start off eating algae and other forms of plankton. As they grow, they eat bigger animals including fish, small aquatic reptiles, and arthropods.
Once they get to stage 3 of the larval form, the lungs have matured enough for them to start breathing through their lungs. As such, they reabsorb their external gills. And as the tail gets longer and more muscular, the tail fan gets reabsorbed. Once both the external gills and the tail fan have been reabsorbed, they are adults and they move from the water onto the land and live their adult lives a lot like that of a lizard.
The adults keep growing for a while. They also eat smaller reptiles and arthropods, so their diet is very similar to the larval diet. Occasionally, an adult will eat fish, but this normally occurs only when they are swimming from one place to another. When they are ready to lay their eggs, they go to a nearby pond, swim to a good location, and then lay their eggs.
Is this plausible? An amphibious reptile? Or would this just be an amphibian, despite them growing scales from their smooth larval skin and not needing to keep their skin moist as adults?