Even though it's technically classified as a "false" saber-toothed cat, Eusmilus possessed truly gigantic canines, which were almost as long as its entire skull (when they weren't in use, this cat kept its killer teeth cozy and warm in specially adapted pouches on its lower jaw). Eusmilus' jaw muscles were comparatively weak--with its huge canines, this prehistoric cat didn't need to inflict a powerful bite--and it was strangely lacking in supplementary teeth, with a relatively paltry two dozen or so. Proving that saber-toothed cats preyed on each other as well as on other mammals, a skull of Nimravus has been identified bearing two Eusmilus-sized bite marks!

Read more about prehistoric mammals like Eusmilus: Saber-Toothed Cats - The Tigers of the Prehistoric Plains

Photograph of Eusmilus: National Parks Service

Protoceratops wasn't nearly as big as most people think: today, this dinosaur is often mistakenly depicted as a giant, but in fact it was only about three feet tall and weighed in the neighborhood of 400 pounds--meaning Hulk Hogan might have been able to wrestle one to the ground. It's believed that large herds of these pig-sized ceratopsians roamed the plains and woodlands of late Cretaceous Asia, where they were preyed on by hungry tyrannosaurs and raptors.

As tiny as it was compared to later herbivorous dinosaurs, Protoceratops lay near the trunk of a mighty dinosaur evolutionary tree, giving rise to the giant ceratopsians of the later Cretaceous period--including such famous and familiar dinosaurs as Triceratops, Centrosaurus and Styracosaurus. However, Protoceratops wasn't the most "basal" ceratopsian; that honor probably belongs to the much earlier Psittacosaurus, if not an even more primitive genus.

Read more about dinosaurs like Protoceratops: Ceratopsians - The Horned, Frilled Dinosaurs

Illustration of Protoceratops: Nobu Tamura

Some major differences existed between the pterosaurs of the late Jurassic period and their Cretaceous descendants: the earlier genera were tiny, small-beaked and long-tailed, while later behemoths like Pteranodon and Quetzalcoatlus possessed enormous beaks and wingspans, relatively short tails, and probably spent as much time walking as flying.

The importance of Darwinopterus (over 20 fossils of which have been discovered in northeastern China) is that it's considered to be a transitional form between these two broad classifications of pterosaur. This flying reptile had an unusually large head and beak, but a relatively puny body with a long (i.e., primitive) tail. As one paleontologist has been quoted as saying, it's "a really cool creature, because it links the two major phases of pterosaur evolution."

Read more about pterosaurs like Darwinopterus: Pterosaurs - The Flying Reptiles

Illustration of Darwinopterus: Nobu Tamura

An odd reversal of the usual pattern with megafauna mammals, Eurotamandua wasn't much bigger than modern anteaters; in fact, this three-foot-long creature was considerably smaller than the Giant Anteater, which can attain lengths of over six feet. However, there's no mistaking Eurotamandua's insect diet, which can be inferred from its long, tubular snout; powerful, clawed front limbs (which it used for digging up anthills); and muscular, gripping tail (which held this mammal in place as it settled in for its meal). What's less clear is whether Eurotamandua was a true anteater or a prehistoric mammal more closely related to modern pangolins; paleontologists are still debating the issue.

Read more about prehistoric mammals like Eurotamandua: The Giant Mammals of the Cenozoic Era

Illustration of Eurotamandua: Wikimedia Commons