If for some reason you’re looking for an actual animal from the actual fossil record that’ll make you go “huh,” then Atopodentatus should probably do the job for you.
Atopodentatus was a reptile from the Triassic, found in China and described in 2014. On the whole it looked like a more or less standard aquatic reptile, something like a big iguana… but there was something really, really wrong with its head.
Scary as this beast looked, that funky jawline full of fangs would have been largely harmless to anything much bigger than a bug. It seems this thing was a filter feeder, using that immobile vertical “mouth” in its upper beak as a trap for the worms or shrimp or whatever it likely scraped up from the mud on the ocean floor.