That is Megapiranha, which lived 8 to 10 million years ago in the rivers of South America and grew to a meter in length, four times that of the cow skeletonizers of today. And if it ever finds out we gave it a lazy-ass name like "megapiranha," it'll find a way to revive itself and tear us to shreds in one or two bites.
Pretty sure this diagram is mistaken on the whole "swimming with man-eaters" thing.
See, not only was Megapiranha huge, but its bite was among the strongest in history, with a force-to-body-weight ratio unmatched by even the mightiest dinosaur. Whereas modern-day piranhas peak at a bite force of 70 pounds, a Megapiranha is estimated to have bitten with a force of 1,000 pounds.
To further illustrate how insane that is, a T. rex could deliver a bite force of just over 3,000 pounds, roughly three times that of a Megapiranha. Only thing is, the T. rex weighed seven tons. The Megapiranha? Twenty pounds, maybe 25 if it started slacking off at the gym. If it were as big as T. rex, it probably could've chewed up an Apatosaurus and swallowed it whole, while barely breaking a sweat.
And here's our friend's bite when compared to other feared creatures of the sea:
There were 47 more entries, but the Megapiranha ate them all.