230 MYH
Aquapterygians are fully aquatic pinniped descendants that have taken up various marine niches. They still have four fins and short tails.
a) The coastal ocean dragon (Thalassodraco plesiosauroides) is a species of plesiosaur-like Dolichopterygian that mainly hunts small fish. These predators lived in what was then Japan and Australia.
b) The long-finned neowhale (Novobalaena anisopteryx) is a species of Novobalaenid Brachyptergian that fills the niches left by the baleen whales. They're about 90 tons in mass and live in what was then Antarctica, Peru, Chile, Brazil, and Canada.
c) Shorcas (Neorca neorca) are the sole living members of the family "Neorcidae," once a much larger group but now relegated to this one species. They are a worldwide taxon and exist as the apex predator in many ocean ecosystems on this future Earth.