What Is a Prehistoric Animal?

Prehistoric animals are all organisms that walked—or swam, crawled, slithered, or flew—on Earth more than 5,500 years ago, before humans started recording history. The earliest known remains date to the Cambrian era, about 600 million years ago, although simple-celled organisms have been around much longer.

Crustaceans, flying reptiles, dinosaurs, woolly mammoths, and saber-toothed tigers are just a few of the hundreds of millions of prehistoric animals that once lived on Earth. Paleontologists know about these animals by studying fossils, animal remains that have been preserved in rock.

Tusoteuthis was a giant squid nearly equal in size to those that ply the oceans today—with their tentacles stretched out, the ancient cephalopods may have measured 25 to 35 feet (8 to 11 meters) long. Like the modern giant squid, Tusoteuthis lacked an outer shell and is known only from discoveries of the rigid support structure in its body called a pen or gladius. The pen was akin to a backbone but made of delicate shell-like material called chitin.

The pen supported a fleshy body with large eyes, a sharp beak, and presumably ten arms lined with suckers that made Tusoteuthis a formidable predator in the Late Cretaceous seas. Smaller cephalopods and fish were likely dietary staples, though small marine reptiles that visited the ocean depths may have fallen prey as well.

Tusoteuthis moved via jet propulsion—it expelled water through a siphon on the lower part of its body. Squirts of dark inky fluid sometimes helped the squid blind and confuse predators like the mosasaur Tylosaurus and a barracuda-like fish called Cimolichthys long enough for escape.

Fast Facts

Type: Invertebrate
Diet: Carnivore
Size: Length, 20 ft (6 m)
Did you know? A partial fossil of the predatory fish Cimolichthys contains a nearly complete backbone-like Tusoteuthis pen.
Protection status: Extinct
Size relative to a bus:

Xiphactinus was one of the largest bony fish of the Late Cretaceous and is considered one of the fiercest creatures in the sea.

A powerful tail and winglike pectoral fins shot the 17-foot-long (5-meter-long) monster through the surface waters of the ocean. Unlucky fish and unsuspecting seabirds were snared inside Xiphactinus's upturned jaw, which was lined with giant, fanglike teeth, giving it an expression akin to that of a bulldog.

A 13-foot-long (4-meter-long) Xiphactinus could open its jaw wide enough to swallow six-foot-long (two-meter-long) fish whole, but it itself was occasionally prey to the shark Cretoxyrhina.Xiphactinus trolled an ancient ocean called the Western Interior Seaway, which covered much of central North America during the Cretaceous. Though long extinct, if alive today the bony fish would look like a giant, fanged tarpon.

Fast Facts

Type: Fish
Diet: Carnivore
Size: Length, Up to 17 ft (5 m)
Did you know? A Xiphactinus on display at a museum in Kansas has a complete, well-preserved fish inside it. Scientists believe the struggling prey ruptured an organ of its captor as it was swallowed, killing the larger fish.
Protection status: Extinct

From: National Geagraphic