Ancient kangaroos didn't hop and 15 other weird prehistoric animal facts

Oh, ancient Earth, your animal kingdom was wonderfully weird.

Take the kangaroo. More than 30,000 years ago, a forerunner of our modern-day hippity-hopping mammal probably didn't hop at all, researchers say; it was just too bulky. Instead, the quarter-ton "short-faced giant kangaroo" loped around on two legs.

Here are 13 other cool facts about prehistoric animals, both great and shrunken.

Since the Ice Age favorites were roughly the size of today's African elephants, the logic follows that mammoths were the equals of elephants in the eating and waste-elimination departments.

Today, the giant armadillo tops out at about 5 feet long and 70 pounds. Four million years ago, the glyptodent, a presumed forerunner of the armored mammal, was as big as a compact car.

You'd have to look closely, very closely, at the skeleton of a 50-million-year-old Pakicetus to understand why it's called the "first whale." The furry, four-legged, land-lubber sported "an ear bone with a feature unique to whales," per the American Museum of Natural History.

A recent fossil find shows that the one-horned Elasmotherium sibiricum, a rhino known as the Siberian unicorn, was among us as recently as 29,000 years ago. Previously, scientists thought the beast had gone extinct 350,000 years ago.

Since theropod dinosaurs, like the triceratops and Tyrannosaurus rex, are presumed ancestors of the modern-day bird, they "more than likely" shared the latter's affinity for mating dances, paleontologist Jack Horner told National Geographic.

A recently uncovered 30-foot-long, 6,000-pound Machimosaurus rex "definitely was at the top of the food chain" of ancient Tunisia, scientists say. It especially liked to snack on turtles.

Some 430 million years ago, the Aquilonifer spinosus "carried its young in capsules tethered to the parent's body like tiny, swirling kites," per a research summary from Yale University.

Scientists nicknamed the arthropod "The Kite Runner."

For decades, scientists could not figure out what the Tully monster was exactly. A worm? A fish? An arm with teeth on the end? Finally, researchers cracked the case: The Tully "monster" was a 300-million-year-old vertebrate...and forerunner of the lamprey.

Actually, scientists say all sorts of mammals got smaller during two heat-up periods 53 to 55 million years ago. The hyracotherium, an early horse, saw its dog-size frame shrink by 19 percent and then another 30 percent.

A dog graveyard in Siberia, possibly 8,000 years old at the time of its discovery, showed that back in the day, humans ate pooches, ritually killed pooches...and occasionally kept them as treasured little fuzzy-wuzzies.

Eleven feet tall. Some 3,500 pounds. No, you wouldn't have wanted to run into the plus-size Arctotherium angustidens, or short-faced bear, on an Argentinian hiking trail 2 million years ago. (Wired assures us the bear wasn't "hypercarnivorous," but still...)

This reptile of 250 million years ago sported a fan-like sail on its back. According to About.com's Bob Strauss, the larger the sail, the "more attractive" the male dimetrodon was to the female.

Dinosaurs that sported bony crests or other ornamentation on their massive heads, such as the Allosaurus, got bigger faster than their plainer counterparts. "Something about their world clearly favored bling and big bods," North Carolina State University scientist Terry Gates says.

Now, we don't think the dinosaurs had trouble sorting themselves out. But human scientists have really struggled with gender-typing. That's why the recent find of a fossilized pregnant Tyrannosaurus rex has been hailed as a big deal.