Titanoboa:
This snake was colossal, enormous. Essentially, after the dinosaurs became extinct, this giant thing took their place as the largest, most vicious predator on earth.
They were 15 meters long, weighed 1 ton, and killed their prey by constriction. Pretty scary, huh?
Dunkleosteus:
Dunkleosteus lived 360 million years ago. It was a heavily armored fish that exceeded 10 meters in length. Its beak-like mouth was specifically designed to penetrate thick, similar armor, suggesting it may have been a cannibalistic species.
Its jaws were so efficient that it could open and close them in milliseconds.
It's still unclear what the entire body of a Dunkleosteus looked like, but we imagine that very few other ancient animals ever lived after it was discovered.
Deinosuchus:
Deinosuchus means "terrible crocodile," and these creatures truly were. Fossils of T. rex and other dangerous dinosaurs show teeth marks from Deinosuchus . This means that ancient crocodiles regularly fought the king of the dinosaurs. Deinosuchus measured up to 10 meters long and was found in North America... in the same places where modern humans evade crocodiles a quarter of their size.
Deinosuchus
fought
T. rexes (and won).
Arcdotus:
A name like "short-faced bear" sounds cute. Arcdotus was anything but. Native to California until about 11,000 years ago, they were almost entirely carnivorous, needing about 35 pounds of meat a day to survive. They were 50% larger than the largest polar bears in recorded history . A bear twice your height.
Megalodon:
The Megalodon makes the great white shark look like a goldfish. (In this photo, the scientist is holding a modern shark's jaw for comparison.) Nearly 20 meters long, these extinct ocean predators are still considered "the most formidable carnivore that ever lived."
Phorusrhacidae:
Scientists call Phorusrhacidae " terror birds ," a name that is quite self-explanatory.
No? OK: They lived in North and South America until about 2 million years ago; they could grow up to 3 meters tall; and their beaks were so strong and sharp that they could kill other animals by hitting their heads downward, fatally cracking their skulls.
Meganeura:
What's so scary about a dragonfly? If you were a smaller insect, or one of the amphibians or other vertebrates milling around a pond hundreds of millions of years ago, you absolutely wouldn't want to be spotted by a Meganeura, the largest known flying insect, which had a wingspan of about 1 meter. They lived at the same time as the Arthropleura, a period known as the Carboniferous. "This experiment in gigantism probably only lasted maybe 30 million years or so," says Labandeira. The enormous arthropods either became extinct or evolved to become smaller, and again, no one is exactly sure why. The oxygen content of the atmosphere decreased, but large amphibians were also developing: "One theory is that it gave rise to much larger vertebrates that were able to consume these things, so size was no longer an adaptive trait," says Labandeira.