Killer whale. No other possibility really, the megaladon is extinct.
Based on what happened to the tag, probably not. Orcas don’t dive deep when they’re eating, and they spend more time on the surface than deep down. Whatever ate this shark hit it, pulled it deep immediately, stayed down there a while, then only occasionally went back to shallow depths over the next few days.
1. "No other possibility" ... actually, there's no possibility that it was a killer whale because the thing that ate this dove almost twenty times deeper than killer whales do. The pressure of that depth would probably kill the Orca pronto.
2. "... the magaladon is extinct" -- according to the same set who thought the Coelacanth was had been extinct for the past 65 million years. OOPS!!! They were wrong. And they may well be wrong about other critters.
My dad, who was a total non-believer when it came to flying saucers and ghosts, made his living fishing the high seas, many hundreds of miles from shore, for more than three decades. He often told me that there are MANY strange and wondrous creatures in the ocean not yet known to science.