20 Ancient Animals That Ruled the Earth Before Humans

Fascinating prehistoric animals, birds, and dinosaurs

Co-authored by Marco Wendt and Samantha Fulton, BA

Last Updated: June 8, 2026 Fact Checked

You’re probably familiar with the Velociraptor or the Milodon, but have you heard of the Plesiosaurus or the Entelodont? In this article, we’ll be covering 20 of the most fascinating ancient animals from prehistoric times. We’ll cover dinosaurs, marine animals, land mammals, and birds. Keep reading for the coolest prehistoric animals, when they lived, and where they were found!

Fascinating Prehistoric Animals

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An illustration of ancient animals, including dinosaurs, marine animals, mammals, and birds.

Ankylosaurus: An armored dinosaur with a heavy club tail
Megalodon: The largest shark to ever live
Plesiosaurus: A marine animal that inspired the legend of the Loch Ness monster
Ambulocetus: A semi-aquatic, 4-legged “walking whale”
Mirarce: A sturdy 2-foot-tall bird with massive wings

1

Megalosaurus

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The Megalosaurus was a theropod that was likely about six meters long. Appropriately, its name literally means “big lizard.” The Megalosaurus was one of the first dinosaurs ever discovered and the very first dinosaur in history to be given a name.^{[1]
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- When it lived: Mid Jurassic period (166 million years ago)
- Diet: Carnivorous
- Found in: England

2

Apatosaurus

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The Apatosaurus was a long-necked, long-tailed dinosaur (a sauropod). Apatosaurus is Greek for “deceptive/false lizard,” named for its unbelievably large size. Paleontologists suspect it weighed over 30 tons!^{[2]
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- When it lived: Late Jurassic period (150 million years ago)
- Diet: Herbivorous
- Found in: North America

3

Velociraptor

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The Velociraptor was a fast, clever predatory dinosaur. It had more than 60 teeth and a pair of sickle-shaped, retractable “killing claws.” Scientists believe the Velociraptor was a fierce predator.^{[3]
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- When it lived: Late Cretaceous period (80 million years ago)
- Diet: Carnivorous
- Found in: Mongolia and China

4

Brachiosaurus

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The Brachiosaurus was a very tall, long-necked dinosaur. Its name means “arm lizard.” Scientists believe the Brachiosaurus fed on tall trees, such as conifers and tree ferns. However, since they couldn’t chew, the Brachiosaurus would swallow leaves whole and break down its food using hindgut fermentation. This is when an animal has a special area in its intestines where tiny bacteria can break down food.^{[4]
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- When it lived: Late Jurassic period (152-145 million years ago)
- Diet: Herbivorous
- Found in: North America

5

Ankylosaurus

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The Ankylosaurus was an armored dinosaur covered with bony plates. It also had a heavy club at the end of its tail. While scientists have yet to find an entire Ankylosaurus skeleton, it is believed to be one of the biggest members of the ankylosaur group (armored dinosaurs).^{[5]
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- When it lived: Late Cretaceous period (68-66 million years ago)
- Diet: Herbivorous
- Found in: North America

6

Mosasaurus

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The Mosasaurus was a marine reptile that could grow up to 15 meters long (half the length of a football field. It was an apex predator with a sleek body and powerful, paddle-like limbs. The Mosasaurus had up to 100 teeth and is related to modern-day lizards and snakes.^{[6]
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- When it lived: Late Cretaceous period (88-66 million years ago)
- Diet: Carnivorous
- Found in: Oceans around the world

7

Plesiosaurus

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The Plesiosaurus was a massive marine animal with a neck that made up half the length of its body. They could grow up to 43 feet (the size of a very large bus) and had 4 flippers. While there’s no evidence that they still exist, plesiosaurs are thought to be the origin for legends like the Loch Ness monster.^{[7]
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- When it lived: Triassic to Cretaceous period (203-66 million years ago)
- Diet: Carnivorous
- Found in: Oceans around the world

8

Helicoprion

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The Helicoprion was a shark-like marine animal with a circular saw-like shape at the end of its lower jaw. This circular set of teeth puzzled scientists for over a century because there were few other remains of the Helicoprion. However, it was recently confirmed that the circle saw teeth would rotate outward when the Helicoprion opened its mouth and then turned backward to tear up its prey.^{[8]
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- When it lived: Early to Middle Permian period (290-270 million years ago)
- Diet: Carnivorous
- Found in: Oceans around the world

9

Megalodon

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The Megalodon was the largest shark to ever live and one of the biggest fish until the species went extinct. They could grow up to 60 feet long, which is three times larger than the typical great white shark. While it is often portrayed as a big version of a great white, scientists believe it was part of a separate lineage. It had a more compact jaw, longer fins, and a shorter nose than the great white.^{[9]
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- When it lived: 23-3.6 million years ago
- Diet: Carnivorous
- Found in: Oceans around the world

10

Megatherium

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The Megatherium was a giant ground sloth. They were up to 10 times the size of modern sloths— that means they could’ve been up to 12 feet tall when standing on hind legs! They could also weigh up to 4 tons. Some Megatherium fossils have been found with cut marks, indicating that they overlapped with humans, who likely hunted and ate these giant sloths.^{[10]
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- When it lived: Middle Pleistocene to early Holocene (400,000-8,000 years ago)
- Diet: Herbivorous
- Found in: South America

11

Chalicotheriidae

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The Chalicotheriidae was a perissodactyl (hoofed mammal with an odd number of toes) closely related to rhinoceroses, tapirs, and horses. Unlike other perissodactyls, the Chalicotheriidae had secondarily evolved claws. Scientists believe they may have browsed from trees like gorillas or giant sloths.^{[11]
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- When it lived: Eocene to Early Pleistocene period (48.6 million to 781,000 years ago)
- Diet: Herbivorous
- Found in: Africa, Asia, Europe, and North America

12

Ambulocetus

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The Ambulocetus was a semiaquatic “walking whale.” Hippos and whales both descended from this 4-legged aquatic mammal. It was about 11-12 feet long and had short legs with flipper-like hind feet. The Ambulocetus weighed about 400 pounds!^{[12]
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- When it lived: Early Eocene period (48-49 million years ago)
- Diet: Carnivorous
- Found in: Pakistan

13

Entelodont

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The Entelodont was a hoofed mammal with bone-crushing jaws and strong legs. The name means “terminator/hell pig.” Despite the name, the Entelodont is actually more closely related to the whippomorphs (which include hippos and whales). Entelodonts were tank-like grassland predators that could take prey up to the size of rhinos.^{[13]
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- When it lived: Eocene, Oligocene, and early Miocene period (38-16 million years ago)
- Diet: Carnivorous
- Found in: Asia, Europe, and North America

14

Smilodon

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The Smilodon was a saber-toothed cat. It had giant canines, or “sabers,” that extended inches past its chin line when its mouth was closed. Some scientists believe the Smilodon was a scavenger rather than a hunter. Either way, it had to open its lower jaw to a 95-degree opening to clear the tips of its saber teeth.^{[14]
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- When it lived: Pleistocene to early Holocene period (2.5 million to 10,000 years ago)
- Diet: Carnivorous
- Found in: North America

15

Myotragus

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The Myotragus was a large mouse-goat mammal. It had skeletal characteristics similar to cattle, sheep, and goats (such as the presence of horns). However, it also had an incisor tooth much like the ones possessed by mice and other rodents. Scientists theorize that these rodent-like incisors acted as a branch-clipping device.^{[15]
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- When it lived: Late Pliocene period (5.3-5.7 million years ago) to about 3,000 years ago
- Diet: Herbivorous
- Found in: Balearic Islands of Mallorca and Menorca in the western Mediterranean

16

Archaeopteryx

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The Archaeopteryx was a bird with broad wings, sharp teeth, and fierce claws. It is the oldest and most primitive bird in the fossil record. It looked like a miniature velociraptor and spent much of its time on the ground, despite having wings.^{[16]
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- When it lived: Late Jurassic period (150 million years ago)
- Diet: Carnivorous
- Found in: Europe

17

Longipteryx

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The Longipteryx had a long beak with pointy teeth and was only 6 inches long. With broad wings and long tail feathers, it could fly with grace and stamina. Paleontologists believe its teeth allowed the Longipteryx to use its beak as a weapon.^{[17]
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- When it lived: Early Cretaceous period (120 million years ago)
- Diet: Herbivorous
- Found in: Northeast China

18

Ichthyornis

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The Ichthyornis was a noisy and aggressive bird similar to a gull. It traveled in dense flocks and was one of the strongest fliers of its time. Ichthyornis were seabirds and left countless fossils along shorelines.^{[18]
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- When it lived: Late Cretaceous period (95-83.5 million years ago)
- Diet: Carnivorous
- Found in: North America

19

Mirarce

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The Mirarce was a bulky bird that stood 2 feet tall. It had sturdy legs and robust wings and was bigger than some members of the velociraptor clan. The Mirarce was able to hunt on the ground, navigating brush and mud, but also had large enough wings to fly with ease.^{[19]
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- When it lived: Late Cretaceous period (75 million years ago)
- Diet: Carnivorous
- Found in: North America

20

Vegavis

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The Vegavis was an aquatic bird, closely related to the duck. It spent much of its time wading and swimming and likely lived along the shore. Fossils of the Vegavis skeleton containing tissue from the voice box tell us that the duck-like bird probably honked and quacked.^{[20]
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- When it lived: Late Cretaceous period (70-66 million years ago)
- Diet: Carnivorous
- Found in: Antarctica

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Zookeeper and conservation educator Marco Wendt points out that some of the animals we still see today existed in prehistoric times. “Birds are modern-day dinosaurs,” he says. “They’re an extension of a type of dinosaur,” and show us how they were able to survive and continue on Earth. He adds that the California Condor thrived during the time of the saber-toothed tiger and woolly mammoth, and it’s still around today.^{[21]
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Wendt adds that the crocodile, alligator, and great white shark are all examples of animals that have existed since prehistoric times. “We need to respect all these wonderful animals that have been around since what we deem as prehistoric,” he says.^{[22]
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