Though believed extinct for over 3 million years, the prehistoric shark Carcharocles megalodon is often tied to the mysterious depths of the Mariana Trench. Fishermen and deep-sea crews have reported massive shadows and enormous bite marks on whales and submarines, far larger than any known shark today. Viral videos and sonar anomalies occasionally resurface online, fuelling speculation that a relic population could lurk in the trenches extreme depths.