The beast-fish was terrifying. It stretched at least 14 feet long—or maybe 18. Its enormous head was shaped like a leopard, or a dog, or an otter, depending on who you asked and when. It used its strong, wide tail to steer through the currents of East Africa’s rivers. Some reported it had the long, white tusks of a walrus and an armadillo’s impenetrable scales. Its feet—for yes, the beast-fish had feet—were as large as a hippo’s, but with the sharpened claws of a T. Rex. As for its legs:…