All these titans existed, although not in the same place or period.
Read on for pictures and more about the biggest animals of all time.
Biggest Snake Discovered; Was Longer Than a Bus
The world's biggest snake was a massive anaconda-like beast that slithered through steamy tropical rain forests about 60 million years ago, says a new study that describes the ancient giant.
Fossils found in northeastern Colombia's Cerrejon coal mine indicate the reptile, dubbed Titanoboa cerrejonesis, was at least 42 feet (13 meters) long and weighed 2,500 pounds (1,135 kilograms).
"That's longer than a city bus and … heavier than a car," said lead study author Jason Head, a fossil-snake expert at the University of Toronto Mississauga in Canada and a research associate with the Smithsonian Institution.
Previously the biggest snake known was Gigantophis garstini, which was 36 to 38 feet (11 to 11.6 meters) long. That snake lived in North Africa about 40 million years ago.
Hans-Dieter Sues, associate director for research and collections at the Smithsonian's National Museum of Natural History, was not involved with the study but has seen the snake fossils.
Sues noted that humans would stand no chance against one of these giants, which killed their prey by slow suffocation.
"Given the sheer size—the sheer cross-section of that snake—it would be probably like one of those devices they use to crush old cars in a junkyard," Sues said.
In addition, the snake's heft indicates that it lived when the tropics were much warmer than they are today, a find that holds potential implications for theories of once and future climate change.
Bull-Size Rodent Discovered -- Biggest Yet
A one-ton "fossil rat" has been discovered in South America, scientists announced .
The prehistoric, bull-size creature—the world's largest recorded rodent—has been identified from a well-preserved skull.
The megarodent lived in lowland rain forests between two and four million years ago, perhaps using its massive teeth to fend off saber-toothed cats and giant, flightless, meat-eating birds, researchers say.
The newfound species, called Josephoartigasia monesi, is reported today in a study led by Andrés Rinderknecht of the National Museum of Natural History and Anthropology in Montevideo, Uruguay.
The rodent weighed about 2,200 pounds (1,000 kilograms), based on an analysis of its 21-inch-long (53-centimeter-long) skull, according to the study, published in the new issue of the journal Proceedings of the Royal Society: B.
Found by an amateur paleontologist in a cliff face along Uruguay's southern coast, the skull suggests that the species was twice as heavy as any other known rodent, Rinderknecht said in an email.
"The future can bring big surprises. But at present J. monesi is the largest recorded rodent," he said.
A relative of rats, mice, and guinea pigs, the creature measured some ten feet (three meters) long, nose to tail. The ancient animal looked a lot like the capybara, the world's largest living rodent, also from South America. (Watch video of an anaconda hunting a capybara.)
But the prehistoric mammal belonged to a rodent family with a single surviving member—the pacarana (see photo)—the study says. A rare species weighing up to 33 pounds (15 kilograms), the pacarana is confined to tropical forests in central South America.
J. monesi inhabited forests around river deltas or estuaries, the study suggests.
"It probably fed on aquatic plants and fruits, because its molars are small and not good for grass or other abrasive [vegetation]," Rinderknecht said.
Giant "Frog From Hell" Fossil Found in Madagascar
Scientists working in Madagascar found what may be the largest frog that ever lived, National Geographic News reported a year ago.
The bad-tempered Beelzebufo, or "devil frog" was a "rather intimidating animal the size of a beach ball, 16 inches (41 centimeters) high and weighing about 10 pounds (4.5 kilograms)."
Paleontologist David Krause of Stony Brook University in New York and his colleagues began unearthing the the 70-million-year-old frog as a specimen in bits and pieces more than a decade earlier. "Over the years a 75-piece puzzle emerged that was only recently put together by fossil-frog expert Susan Evans of University College London," National Geographic's story said.
Evans, lead author of a paper detailing the find, said that, like its closest modern-day relatives -- a group of big-mouthed frogs in South America called ceratophyrines -- the devil frog also probably had a very aggressive temperament."These ceratophyrines are really aggressive, ambush predators. They are round with big mouths, and they will sit there and grab onto anything that walks past."
"They're sometimes called Pac-Man frogs," she added, "and even the little ones will go for you. It's a frog with attitude, even today. And at two or three times the size of the largest living ceratophyrines, Beelzebufo would have had quite a lot more attitude."
The animal sported a protective shield and powerful jaws that may have enabled it to kill hatchling dinosaurs, National Geographic News reported.
Giant Penguins Once Roamed Peru Desert, Fossils Show
Penguins about the size of humans roamed South America some 35 million years ago, and they didn't need ice to survive.
That's the result of a new study by North Carolina State University paleontologist Julia Clarke and her colleagues.
The study, which appears in this week's issue of the Proceedings of the National Academy of Sciences, unveils two new species of giant penguins from fossils unearthed in Peru's Atacama Desert.
The discovery pushes the date of penguin migration to equatorial regions back more than 30 million years, to one of the warmest periods of the last 65 million years.
The find also casts doubt on climate as the main factor in penguins' choice of habitat through history.
"The public is very familiar with the image of penguins and icebergs," Clarke said.
Today's penguins are cold-adapted and therefore at grave risk from global warming, she said, but the new fossils suggest that hasn't always been true.
(Clarke's research was funded by the National Geographic Society's Expeditions Council. National Geographic News is a division of the National Geographic Society.)
The new study describes two new species of penguins from fossils, including the first complete skull from an ancient giant penguin.
That species, which the authors say lived in Peru about 36 million years ago, is the third largest penguin known and stood about 4.5 feet (1.5 meters) tall.
The other, dating to 42 million years, was about three feet (a meter) tall, which is comparable to the today's second largest living penguin, the king penguin.
Giant Sea Scorpion Discovered; Was Bigger Than a Man
Scientists said this 18-inch (46-centimeter) fossil claw (bottom) belonged to the world's largest known bug: an 8.2-foot (2.5-meter), 390-million-year-old sea scorpion called Jaekelopterus rhenaniae, National Geographic News reported in November 2007.
"The size of a large crocodile, the 390-million-year-old sea scorpion was the top predator of its day, slicing up fish and cannibalizing its own kind in coastal swamp waters, fossil experts say," our report said.
Jaekelopterus rhenaniae measured some 8.2 feet (2.5 meters) long, scientists estimate, based on the length of its 18-inch (46-centimeter), spiked claw.
"The find shows that arthropods -- animals such as insects, spiders, and crabs, which have hard external skeletons, jointed limbs, and segmented bodies -- once grew much larger than previously thought," said paleobiologist Simon Braddy of the University of Bristol in the United Kingdom. "We have known for some time that the fossil record yields monster millipedes, supersized scorpions, colossal cockroaches, and jumbo dragonflies," he added. "But we never realized, until now, just how big some of these ancient creepy-crawlies were."
The fossilized claw of the sea scorpion was uncovered in a quarry near Prüm in Germany.
Ancient Giant Shark Had Strongest Bite Ever, Model Says
Prehistoric megalodon—literally "megatooth"—sharks had the most powerful bite of any creature that has ever lived, according to a new model.
Its bite was strong enough to crush an automobile and far exceeded that of the great white shark and even Tyrannosaurus rex.
Known mostly from the large teeth it left behind, Carcharodon megalodon first appeared in Earth's seas about 16 million years ago (in the Neogene period) and dined on giant prehistoric turtles and whales.
"Megalodon's killing strategy was to bite the tails and flippers off large whales, effectively taking out their propulsion systems," said study leader Stephen Wroe of the University of New South Wales in Australia.
The prehistoric shark may have grown to lengths of over 50 feet (16 meters) and weighed up to 30 times more than the largest great white.
"A great white is about the size of the clasper, or penis, of a male megalodon," said Peter Klimley a shark expert at the University of California at Davis, who was not involved with the current research.
"Could Have Crushed a Small Car"
Wroe and his colleagues extrapolated the bite force of megalodon from data they collected from great whites.
The team created a computer model of a great white's skull, jaw, and head muscles from images generated by a computerized tomography (CT) scanner.
They then ran "crash test" simulations with the model to reveal the stresses and strains it could withstand and the strength of its bite.
The team estimated a great white could generate a maximum bite force of about 4,000 pounds (1,800 kilograms).
Because megalodon was much bigger than a great white, it might have chomped down on prey with a force of between 24,000 to 40,000 pounds (10,900 to 18,100 kilograms), the researchers say.
Giant Prehistoric "Kangaroos" Killed Off by Humans
Humans, not climate change, were responsible for the extinction of giant "kangaroos" and other massive marsupials in Tasmania more than 40,000 years ago, according to new research.
Hunting on the Australian island exterminated several prehistoric animals, including the kangaroo-like beasts, marsupial "hippopotamuses," and leopard-like cats, a team of scientists announced. (Learn more about the red kangaroos and hippos of today.)
The giant kangaroo-like Protemnon anak, a long-necked leaf browser, survived on Tasmania until at least 41,000 years ago—much later than previously believed and up to 2,000 years after the first human settlers are believed to have arrived—according to new radiocarbon and luminescence dating of fossils, some of which were accidentally found by cavers.
Previous studies had concluded that Tasmania's giant beasts had already disappeared by the time humans crossed a temporary land bridge to the island 43,000 years ago. These studies blamed the extinctions on climate change—including the last ice age—instead.