1) Class 2) Subclass synapsida 
(from the article `vertebrate`) ...temporal openings high up on skull; fishlike; spindle-shaped body; high tail fin; triangular dorsal fin; paddlelike legs; marine.Subclass ... ...tail (i.e., with the lower lobe longer than the upper). Limbs paddle-like; snout often elongated and beaklike.†Subclass Synapsida (mammal-like ... The...
The synapsida are a subclass of mammal-like reptiles now extinct.
[n] - extinct reptiles of the Permian to Jurassic considered ancestral to mammals
subclass Synapsida noun extinct reptiles of the Permian to Jurassic considered ancestral to mammals