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10 Insanely Large Prehistoric Relatives of Modern-Day Animals

Ricky Rodson is an experienced cryptozoologist with several published books on the subjects of zoology, cryptozoology, and mythical beasts.

The heavily armed Glyptodon (pictured here) is the oldest known relative of the modern-day armadillo.

The heavily armed Glyptodon (pictured here) is the oldest known relative of the modern-day armadillo.

Whether we're talking about plants and animals or serving sizes at fast-food restaurants, things of the past almost always seem to have come in larger sizes. Over the last few million years, the sizes of large animals seem to have declined at a rate that seems almost systematic.

This is lucky for us because, given the sheer size and power behind some of the animals on this list, I do not think we would have been able to survive had they not gone extinct and been replaced by more modestly sized modern predators. The animals on this list demonstrate just how much the world has changed over the millions of years it has existed.

10 Massive Prehistoric Creatures

  1. Megatherium
  2. Glyptodon
  3. Gigantopithecus
  4. Terror Bird
  5. Haast’s Eagle
  6. Archelon
  7. Short-Faced Bear
  8. Deinosuchus
  9. Titanoboa
  10. Megaladon
Compared to the sloths of today, the Megatherium was a real giant.

Compared to the sloths of today, the Megatherium was a real giant.

1. Giant Ground Sloth (Megatherium)

The Megatherium was an enormous ground sloth that used to live in different areas of South America. Existing during the early Pliocene period, this elephant-sized ground sloth is sometimes referred to as the giant ground sloth. In fact, is it so gigantic that there are few land mammals to have ever exceeded its size. This beast of a sloth was originally discovered in Argentina back in 1788 but was not officially identified until the next year when it was looked over by the world-famous paleontologist Georges Cuvier.

Can you imagine if armadillos of today were still the size of their oldest relative, the Volkswagon-sized Glyptodon?

Can you imagine if armadillos of today were still the size of their oldest relative, the Volkswagon-sized Glyptodon?

2. Glyptodon

The massive Glyptodon was a type of large mammal that lived from 2.6 million years ago to about 11,700 years ago. This heavily armored animal is said to be the oldest known relative of the modern-day armadillo.

This living tank was about the size of a small car with a smooth, bony shell and turtle-like limbs. Despite its giant size, the Glyptodon was a peaceful creature that stayed away from danger whenever possible. It grazed near water sources, feeding on mostly dicotyledonous trees and monocotyledonous grasses.

The Gigantopithecus is a massive Asian primate that many people believe inspired folklore like Bigfoot and the Yeti.

The Gigantopithecus is a massive Asian primate that many people believe inspired folklore like Bigfoot and the Yeti.

3. Gigantopithecus

The Gigantopithecus is believed to have lived among the dense bamboo forests of Asia. Its location, along with other evidence based on modern-day primates has led scientists to think that this large ape was a herbivore.

Fossil records prove that the Gigantopithecus is the largest of primates to have ever lived, standing to be nearly 9.8 feet tall and weighing almost as much as 1,320 pounds. Many people alive today claim that the Gigantopithecus may offer a scientific explanation behind such myths as the Tibetan Yeti or the American Bigfoot.

During its time on the planet, the terror bird was known to be a fierce apex predator.

During its time on the planet, the terror bird was known to be a fierce apex predator.

4. Terror Bird (Phorusrhacids)

The terror bird, also known scientifically as the Phorusrhacids, is an extremely large carnivorous bird that has been extinct for nearly two million years. These large beast were the apex predator of South America, taking and eating whatever they wanted.

The downward curve of their beak likely evolved to rip meat from the bodies of animals. These massive birds were able to grow to heights ranging from three to nine feet tall. The closest modern-day relative to the terror bird is the Texas seriemas, which only stands a total of 31 inches tall. My, how the times have changed.

The Haast’s eagle became extinct as recently as 600 years ago.

The Haast’s eagle became extinct as recently as 600 years ago.

5. Haast’s Eagle (Hieraaetus moorei)

The Haast's eagle is a now-extinct species of eagle that was once believed to only be a Maori legend. It is the largest species of eagle to have ever existed and only lived on the South Island of New Zealand.

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The eagle is known to have grown to sizes larger than nine feet and weighed approximately 31 pounds. Its large size was believed to be an evolutionary response to the size of its prey. Haast's eagles went extinct around the 1400s when their primary source of food, the moa, were killed off by humans.

Once believed to be an ancestor of the leatherback turtle, the Archelon was recently determined to be a unique species.

Once believed to be an ancestor of the leatherback turtle, the Archelon was recently determined to be a unique species.

6. Archelon

The Archelon is an extinct marine animal that roamed the waters during the late Cretaceous. This giant turtle is the largest turtle known to have existed at over 15 feet long from head to tail with a 13-foot flipper span. The Archelon also weighed nearly 5,000 lbs.

This enormous turtle was once believed to be the oldest-known ancestor of the leatherback sea turtle but now is known to be of a completely different lineage. It is believed that as waterways began to migrate southward, the Archelon was unable to adapt to the habits of new marine predators, and this eventually led to their extinction.

When compared to modern-day bears, the short-faced bear was so large that it can be hard to imagine.

When compared to modern-day bears, the short-faced bear was so large that it can be hard to imagine.

7. Short-Faced Bear (Arctodus simus)

The Arctodus simus, more lovingly referred to as the short-faced bear, is one of the oldest-known relatives of the modern-day spectacled bear. While the exact date it began to exist remains unknown, the short-faced bear lived in North America for at least 800,000 years and only went extinct about 12,000 years ago.

For the entire span of its existence, the short-faced bear was considered to be the largest land-dwelling species of Carnivora that ever lived in North America. This massive bear's shoulders stood at about five to six feet off the ground, which means that even while walking on all fours, the Arctodus simus would be tall enough to look an average-sized human in the eye.

The Deinoshuchus is a terrifyingly large crocodilian that lived during the Cretaceous period.

The Deinoshuchus is a terrifyingly large crocodilian that lived during the Cretaceous period.

8. Deinosuchus

The Deinosuchus is an extremely large but now-extinct crocodilian that is related to the modern alligator. It thrived for nearly nine million years during the late Cretaceous period (approximately 82 to 73 million years ago). The average male Deinosuchus ranged from 34 to 39 feet in total length and weighed about 2.5 to 5 tons.

Aside from its very large size, the Deinosuchus generally looked the same as any other crocodilian alive today, but that is not to say that size was not a factor. Because of its powerful jaws and large mouth, the Deinosuchus was capable of taking down large dinosaurs given the opportunity. Despite this, the prehistoric alligator probably mainly focused on sea turtles and other aquatic animals for a large portion of its diet.

If you thought the snakes in the movie "Anaconda" was bad, wait until you see the Titanoboa.

If you thought the snakes in the movie "Anaconda" was bad, wait until you see the Titanoboa.

9. Titanoboa

The Titanoboa is a (luckily extinct) species of snake that was capable of growing to terrifying sizes. On average, the snake grew to sizes of to over 40 feet long and weighed over 2,400 pounds.

Because only 28 fossils of this species of snake have been discovered, all of which date back around 58 to 60 million years ago, not much is known about this prehistoric snake's life. Scientists have discovered that despite its large mass, the Titanoboa was mainly piscivorous (it ate fish) by examining the creature's jawline.

The Megaladon is the largest shark to have ever existed.

The Megaladon is the largest shark to have ever existed.

10. Megaladon

The Megaladon is an extinct species of shark that was capable of growing to immense sizes and take out even larger foes. Male Megalodons were known to grow upwards of 35 to 47 feet in length and weigh anywhere from 14 to 37 tons. Females could even larger. They were between 44 and 56 feet long and weighed from 30 to 65 tons. Aside from the size difference, the Megaladon was said to both look and act similar to modern-day great white sharks found in the coastal waters of all oceans.

Resources and Further Reading

This content is accurate and true to the best of the author’s knowledge and is not meant to substitute for formal and individualized advice from a qualified professional.

© 2020 Ricky Rodson

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