After Dinosaurs Went Extinct, These Ten Giant Creatures Roamed the Earth

Dinosaurs have always seemed larger than life. They lived during a time when almost everything seemed bigger—titanic herbivores stretching more than 80 feet long were not uncommon, and nine-ton carnivores had to feast on hundreds of pounds of flesh each day to survive. This popular view of the Age of Dinosaurs overlooks the innumerable small species that lived alongside Stegosaurus and Triceratops, just as we’re surrounded by insects, birds, rodents and other small animals today. It also falsely frames the end of this era as an end to the heyday of gigantism—but that’s only an illusion.

Life didn’t shrink after the end of the Cretaceous. Long past the Age of Dinosaurs, Earth saw the evolution of impressive birds, snakes, crocodiles, rhinos and more, including the largest animals of all time. While the broader story of life on Earth may best be told through the diminutive and meek creatures that are often overlooked, here are ten animals that underscore the fact that remarkable body size was not just the domain of the dinosaurs.

Barylambda

With the non-avian dinosaurs gone, some mammal lineages evolved big body sizes fast, among them an extinct group of mammals called pantodonts. Among the best known of these is Barylambda, an herbivorous beast that lived in western North America between 50 million and 60 million years ago.

Barylambda didn’t look quite like any mammal alive today, perhaps most closely resembling the giant sloths that would evolve tens of millions of years later. And while Barylambda was far from the biggest mammal ever, the eight-foot-long, thousand-pound creature was the biggest mammal in its ancient forested ecosystems. The evolution of this herbivore helps paleontologists mark when mammals began to expand into larger body sizes and create new niches.

Titanoboa

Less than ten million years after the asteroid impact that wiped out the non-avian dinosaurs, the largest snake of all time slithered through the humid swamps of Colombia. Paleontologists appropriately named this serpent Titanoboa (“titanic boa”) cerrejonensis in 2009; the reptile could grow more than 40 feet in length and weigh upwards of 2,000 pounds.

Titanoboa thrived during a time called the Paleocene, a chapter in Earth’s history when life was recovering from a devastating asteroid impact. Just as mammals were diversifying and some were becoming larger, so were reptiles. On a warm, greenhouse Earth, animals that relied on their environment’s temperature to regulate their body heat—like snakes—were able to attain larger body sizes than during cooler times. A lack of large mammals also provided enough ecological space for Titanoboa to expand in size, too, although the reptile probably wasn’t an apex predator of the sort seen in late-night creature features. Titanoboa, paleontologists hypothesize, likely feasted on fish.

Barinasuchus

Time and again, crocodiles have evolved to become immense, impressive hunters. During the Cretaceous, 40-foot ambush predators such as Sarcosuchus and Deinosuchus munched on dinosaurs. Long after, about 13 million years before the present, the huge caiman relative Purussaurus cracked open turtles in ancient South America. But not all the big crocs were ambush predators that lurked at the water’s edge. Between about 15 million and 55 million years ago, the landscapes of ancient Argentina, Peru and Venezuela were prowled by a land-dwelling crocodile that that was larger than even the biggest meat-eating mammals of its time: Barinasuchus arveloi.

First described in 2007, Barinasuchus belonged to a group of crocodiles that evolved in the Cretaceous but truly thrived after the non-avian dinosaurs disappeared. These reptiles, called sebecids, pursued their prey on land and chomped down with flattened, blade-like teeth more similar to those of carnivorous dinosaurs than other crocodiles. While not the largest crocodile of all time, Barinasuchus is estimated to have reached maximum sizes of more than 20 feet long and weighed over 3,000 pounds—comparable to today’s saltwater crocodiles. Given that Barinasuchus fossils are found in rocks spanning a wide region and tens of millions of years, the crocodile must have been an exceptional carnivore.

Paraceratherium

The biggest mammals to walk the Earth never got as big as the largest dinosaurs. Still, it’s difficult to look at the skeleton of Paraceratherium bugtiense and not be impressed. An immense rhino that is a contender for the superlative of “largest land mammal of all time,” the huge herbivore roamed eastern Eurasia between 23 million and 34 million years ago.

Rhinos of various shapes and sizes used to be much more common on Earth, and Paraceratherium was like a rhino rendition of a giraffe. The rhino’s neck stretched more than six feet long, and the beast stood more than 15 feet tall at the shoulder. Despite its relatively slender appearance, though, Paraceratherium was a hefty animal and weighed in the neighborhood of 33,000 pounds. At such size, adult Paraceratherium were too large to be bothered by wolf-sized mammalian carnivores in the same habitats—although Paraceratherium bones hint that 33-foot-long crocodiles took bites out of these immense mammals.

Megalania

One of the largest carnivores to wander Ice Age Australia wasn’t a mammal, but a reptile. Reaching lengths of more than 18 feet, or more than twice the length of a Komodo dragon, Megalania was one impressive lizard.

Paleontologists are unsure exactly how large Megalania was, because so few bones of the monitor lizard have been found. Estimates range from 15 to 26 feet, although even the lower estimate is far larger than any lizard alive today. And based on the lizard’s teeth, Megalania was a fearsome predator. Not only did Megalania have sharp, curved teeth like those of Komodo dragons, but, based on evolutionary relationships, paleontologists hypothesize it had a venomous bite that prevented prey from properly healing their wounds, leaving victims to weaken from blood loss and infection before the final strike.

Elephant bird

Big birds have evolved multiple times since the end of the Age of Dinosaurs, from the seed-eating Gastornis of 50 million years ago to the famous “terror birds” that were apex predators in South America. But largest of all was the elephant bird Aepyornis maximus, a flightless creature that lived on Madagascar more than a thousand years ago.

While several elephant bird species grew to prodigious sizes, Aepyornis maximus was the biggest of all. The bird stood almost ten feet tall and could weigh over a thousand pounds. That makes Aepyornis maximus comparable in size to some non-avian dinosaurs like Utahraptor, although it seems Aepyornis laid much bigger eggs. A single Aepyornis egg could weigh more than 20 pounds, with enough internal volume to hold more than a hundred chicken eggs. Precisely why this impressive avian went extinct is unclear, but it likely stemmed from a combination of climate change, hunting by humans and environmental disturbances created when livestock were introduced to Madagascar.

Pelagornis sandersi

While Aepyornis maximus is currently regarded as the largest bird of all time, the avian was flightless. The largest flying bird lived much earlier, around 25 million years ago, in what’s now South Carolina. With a wingspan stretching 21 feet from tip to tip, Pelagornis sandersi was pushing the limits of how big flying birds can be.

At first glance, Pelagornis sandersi might have looked something like an oversized albatross, but a jagged smile set the bird apart. Pelagornis belonged to a group of birds that evolved spike-like projections of their beaks that resembled the teeth of a bow saw—false “teeth” that helped the birds nab slippery and squirming prey. Based on the proportions of the bird and its rough resemblance to today’s wandering albatross, paleontologists suspect that Pelagornis sandersi spent much of its life soaring long distances over the seas.

Otodus megalodon

Despite the impression that everything was bigger in the age of dinosaurs, some of the largest ocean-dwelling animals of all time evolved in the tens of millions of years after asteroid impact. During the Late Cretaceous, for example, the largest sharks grew up to 25 feet long. But by about 23 million years ago, a much bigger shark had evolved—Otodus megalodon.

While paleontologists have debated the maximum size of Otodus megalodon for decades, recent estimates have placed the shark somewhere between 34 and 52 feet in length—the largest predatory shark ever. Paleontologists have only just begun to understand how this shark grew to such sizes. One recent study suggests that larger Otodus megalodon embryos would eat their smaller womb-mates, similar to sand tiger sharks today. Paired with extremely fast growth rates, this would lead the broad-toothed sharks to become larger over time as they fed on the blubbery whales and other marine mammals of the ancient seas.

Steppe mammoth

Woolly mammoths are the most famous shaggy elephants, but they were not the biggest. The steppe mammoth, known to paleontologists as Mammuthus trogontherii, was the largest of all.

Steppe mammoths wandered much of Eurasia between 200,000 and 1.8 million years ago, and they got big. Some of the largest known specimens were about 15 feet tall at the shoulder, significantly taller than even the largest African bush elephants. And this giant is certainly relevant to the origins of the later mammoth species that spread across the Northern Hemisphere during the Ice Age. Recent genetic studies have indicated that woolly mammoths likely evolved from steppe mammoths, and later interbreeding between woolly mammoths and a lineage of steppe mammoths led to the origins of what paleontologists sometimes call the Columbian mammoth.

Blue whale

The largest animal of all time currently swims the seas. Reaching approximately 98 feet in length and weighing over 200 tons, the blue whale is more massive than any known dinosaur. And the cetacean accomplished this evolutionary feat relatively recently. Blue whales evolved by about 1.5 million years ago, reaching sizes exceeding 85 feet during a time when steppe mammoths were still roaming Eurasia.

Despite being known as ocean giants today, whales only started to evolve truly impressive sizes around 3.6 million years ago, just before the huge shark Otodus megalodon went extinct. That the biggest whale—and animal—of all time is alive today raises the possibility that whales may become even larger over evolutionary time. Size may be limited by everything from diet to how quickly nerves can conduct messages from brain to body and back again, but the largest whales have pushed beyond anything seen before. Every blue whale that still swims in the seas is a reminder that we remain in a time of giants.

Riley Black | | READ MORE

Riley Black is a freelance science writer specializing in evolution, paleontology and natural history who blogs regularly for Scientific American.