An All Yesterdays'd Basking Shark (Cetorhinus maximus). So let’s see…
Basking Sharks can decompose in some strange ways, sometimes reduced to only a spinal column and cranium. So I imagined that ignorant future palaeontologists only had that material to work with.
To make matters worse, the speculative individual is a juvenile, which have really weird snouts. This would probably be speculated to be a species recognition aid.
The shape is inspired by Frilled Sharks, which actually have a similar number of vertebrae (147 to 110 in Baskings) and, when healthy, aren’t really that eel-like.