Prehistoric times were a time of giants.
Almost every animal seemed to be bigger in the past than they were today.
The Mesozoic Era (also known as the age of dinosaurs) saw some of the biggest animals walk the planet.
Dinosaurs grew to astronomical sizes, towering high above all other animals in their ecosystem.
Mammals have been for more than 200 million years, meaning they were there during the time of the dinosaurs.
But Mesozoic mammals weren’t very big.
The mammals rose to prominence after the dinosaurs disappeared, and many giant forms of this group of creatures emerged.
In this article, we’ll list 25 of these intriguing mammals.
25. Smilodon
| Name | Smilodon |
| Name Meaning | “Knife tooth” |
| Pronunciation | SMY-lo-don |
| Era | Cenozoic—Quaternary |
| Classification | Mammalia, Carnivora, Felidae |
| Diet | Carnivorous |
| Height | 1 meter (3.3 feet) |
| Length | 1.5–2.5 meters (5–8 feet) |
| Weight | 160–280 kilograms (350–620 pounds) |
| Location | North America and South America |
The Smilodon is one of the largest and best-known saber-toothed cats—the most dominant terrestrial predators in the Americas from the Eocene to the Pleistocene Epoch.
Like other saber-toothed cats, the Smilodon’s most notable feature was its Long, curved, saber-shaped canine teeth.
The Smilodon was about the same size as some of the biggest cats today but with a heavier and more robust build.
24. Archaeoindris
| Name | Archaeoindris |
| Name Meaning | “Ancient indri” |
| Pronunciation | Ar-kay-o-in-driss. |
| Era | Cenozoic — Quaternary |
| Classification | Mammalia, Primates, Palaepropithecidae |
| Diet | Herbivorous |
| Height | 1.5 meters (4.9 feet) |
| Weight | 230.5 kilograms (508 pounds) |
| Location | Madagascar (Africa) |
Archaeoindris was a giant lemur, about the same size as an adult male gorilla.
It was the largest primate on the Island of Madagascar and also one of the largest primates to have ever evolved (only smaller than the Gigantopithecus).
A maximum weight of about 230.5 kilograms (508 pounds) has been estimated for the Archaeoindris.
It isn’t clear if this giant lemur spent more time on land or hanging in trees, but it is most commonly described as a slow-moving tree-dweller.
23. Gigantopithecus
| Name | Gigantopithecus |
| Name Meaning | “Giant Ape” |
| Pronunciation | Ji-gan-to-pi-the-kus |
| Era | Cenozoic – Quarternary |
| Classification | Primates, Haplorhini, & Simiiformes |
| Diet | Herbivorous |
| Height | 9 to 10 feet (2.7 to 3 meters) |
| Length | N/A |
| Weight | 200–300 kg (441–661 pounds) |
| Location | China (Asia) |
Gigantopithecus holds the spot for the biggest ape that has ever lived.
It lived in Asia during the Pleistocene Epoch.
Gigantopithecus stood at a height of about three meters (10 feet) and weighed up to 300 kilograms (660 pounds).
For context, the biggest gorilla ever recorded in the wild was only six feet (1.83 meters) tall and weighed about 589 pounds (267 kilograms).
Gigantopithecus was a herbivore with a specialized diet.
It mainly ate fruits and a few other plants, such as bamboo, which were quite abundant in its habitat.
22. Amphicyon
| Name | Amphicyon |
| Name Meaning | “Ambiguous dog” |
| Pronunciation | Am-fee-cie-on |
| Era | Cenozoic — Neogene |
| Classification | Mammalia, Carnivora, Amphicyonidae |
| Diet | Carnivorous |
| Height | 1.2 meters (3.9 feet) |
| Length | 2.5 meters (8.2 feet) |
| Weight | 550 kilograms (1,200 pounds) |
| Location | North America, Eurasia, & Africa |
Amphicyon is commonly referred to as the “bear dog.”
However, these carnivorous mammals were neither dogs nor bears, even though they share features of both animals.
The bear dog was one of the top predators of the Miocene Epoch, with different species across Europe, Africa, and North America.
The largest species in the Amphicyon genus weighed about 550 kilograms (1,200 pounds), making it one of the largest meat-eating mammals of all time.
21. Barylambda
| Name | Barylambda |
| Name Meaning | “Bigger Lambda |
| Pronunciation | Ba-ree-lam-da |
| Era | Cenozoic — Paleogene |
| Classification | Mammalia, Cimolesta, Barylambdidae |
| Diet | Herbivorous |
| Height | 1.5 meters (5 feet) |
| Length | 2.5 meters (8.2 feet) |
| Weight | 650 kilograms (1,430 pounds) |
| Location | United States (North America) |
After the dinosaurs went extinct at the end of the Cretaceous, a group of mammals known as the pantodonts rose to prominence to become the largest land animals of the Paleogene.
The Barylambda was one of the biggest members of this group.
It was built like a giant ground sloth with giant bear-like legs underneath its stocky body.
The Barylambda was about the same size as a small horse, with an estimated weight of about 650 kilograms (1,430 pounds).
20. Josephoartigasia
| Name | Josephoartigasia |
| Name Meaning | “Named after Uruguayan national hero José Artigas” |
| Pronunciation | Ho-say-for-ar-tig-a-se-ah |
| Era | Cenozoic — Neogene |
| Classification | Mammalia, Rodentia, Dinomyidae |
| Diet | Herbivorous |
| Height | 1.5 meters (4.9 feet) |
| Length | 2.6 meters (8.5 feet) |
| Weight | 58 kg (130 lbs) |
| Location | South America |
Modern rodents are the smallest mammals around, but they have some pretty big ancestors.
One of such massive rodent ancestors is the Josephoartigasia, which lived in South America from the Early Pliocene to the Early Pleistocene Epoch.
The skull of this giant rodent was as big as that of a beef cow, and its entire body measured up to 2.6 meters (8 feet 7 inches).
The average weight of this rodent has been estimated to be about 480 to 500 kilograms (1,060–1,100 pounds).
Josephoartigasia lived in an estuarine environment and survived on a diet of fruits and soft plants.
19. Arctotherium
| Name | Arctotherium |
| Name Meaning | “Bear beast” |
| Pronunciation | ark-toe-THERE-ee-um |
| Era | Cenozoic — Quaternary |
| Classification | Mammalia, Carnivora, Ursidae |
| Diet | Omnivorous |
| Height | 3.4–4.3 meters (11–14 feet) |
| Length | 2.6 meters (8.5 feet) |
| Weight | 58 kg (130 lbs) |
| Location | South America |
The Arctotherium is one of the largest bears to have ever lived.
The name translates as “bear beast,” referring to the massive size of this giant bear.
Arctotherium lived in North and South America during the Pleistocene.
It was a short-faced bear characterized by a reduced snout compared to their long-faced relatives.
Size estimates vary from the different species in the Arctotherium genus, but the biggest of them weighed up to 751 kilograms (1,656 pounds) and was about 1.5 meters (4.9 feet) tall.
18. Macrauchenia
| Name | Macrauchenia |
| Name Meaning | “Long llama” |
| Pronunciation | Mak-row-chen-e-a |
| Era | Cenozoic — Quaternary |
| Classification | Mammalia, Litopterna, Macraucheniidae |
| Diet | Herbivorous |
| Height | 1.4 meters (4.5 feet)) |
| Length | 3 meters (10 feet) |
| Weight | 1,042.8 kilograms (2,299 pounds) |
| Location | Patagonia, Chile, Venezuela (South America) |
Macrauchenia was an odd-looking ungulate built like a llama or camel but significantly bigger.
It lived in South America during the Pleistocene Epoch and was alive until about 10,000 years ago.
One of the most notable features of the Macrauchenia is its retracted nostrils located almost between the eyes.
Due to the position of the nostrils, the Macrauchenia is often reconstructed with a short trunk similar to that of the tapir.
Macrauchenia weighed about 1,042.8 kilograms (2,299 pounds) and stood at a height of up to 4.5 feet at the shoulder.
17. Daeodon
| Name | Daeodon |
| Name Meaning | “Destructive tooth” |
| Pronunciation | Day-oh-don |
| Era | Cenozoic — Paleogene to Neogene |
| Classification | Mammalia, Artiodactyla, Entelodontidae |
| Diet | Omnivorous |
| Height | 1.77 meters (5.8 feet) tall at the shoulders |
| Length | 3.6 meters (12 feet) |
| Weight | 600–1,000 kilograms (1,300 to 2,200 pounds) |
| Location | North America |
Daeodon was the largest-known entelodont mammal—a group of pig-like mammals that lived during the Eocene and Miocene epochs.
The massive skull of Daeodon measured up to three feet in length, and its neck was muscular.
Like other entelodonts and their modern relatives (pigs), ˆ was omnivorous with a varied diet that included nuts, roots, vines, as well as meat.
The massive jaws of this mammal were also strong enough to crush bones, which makes a scavenger diet possible.
Daeodon lived in the dense forests and grasslands of North America and was among the largest animals in its ecosystem.
16. Andrewsarchus
| Name | Andrewsarchus |
| Name Meaning | “Named after Roy Chapman Andrews and “archus” meaning “ruler” or “monarch.”” |
| Pronunciation | An-droo-sar-kus |
| Era | Cenozoic—Paleogene |
| Classification | Mammalia, Artiodactyla, Andrewsarchidae |
| Diet | Carnivorous |
| Height | 1.8 meters (6 feet) |
| Length | 4.8-5.5 meters (16-18 feet) |
| Weight | 500-1000 kilograms (1,100-2,200 pounds) |
| Location | Mongolia and China (Asia) |
Andrewsarchus was a giant mammal commonly regarded as the largest terrestrial, carnivorous mammal ever.
It lived in Asia during the Eocene Epoch.
Andrewsarchus weighed about 2,200 pounds and stood over six feet tall at the shoulders.
This mammal is known from fragmentary skull fossils, making it difficult to reconstruct its exact appearance and relationship with living mammals.
However, experts think the Andrewsarchus is probably related to living hippos and whales.
15. Doedicurus
| Name | Doedicurus |
| Name Meaning | “Stout tail” |
| Pronunciation | dee-DIK-yoo-rus |
| Era | Cenozoic – Quaternary |
| Classification | Mammalia, Xenarthra, Glyptodontidae |
| Diet | Herbivorous |
| Height | 1.5 meters (4 feet 11 inches) |
| Length | 3.6 meters (12 feet) |
| Weight | 1,400 kilograms (3,100 pounds) |
| Location | South America |
Doedicurus was a giant armored mammal related to modern armadillos.
It lived in South America during the Pleistocene Epoch and was one of the biggest animals on the continents at the time, with an estimated weight of up to 1,400 kilograms (3,100 pounds).
Doedicurus had a large, domed shell on its back that protected it from predators.
It also had a massive tail club with spikes that weighed up to 40 kilograms (88 pounds).
The Doedicurus could swing this massive tail at predators to defend itself.
It was a herbivore with large claws and teeth for processing plant materials.
14. Chalicotherium
| Name | Chalicotherium |
| Name Meaning | “Gravel beast” |
| Pronunciation | Kuh-lik-uh-THEER-ee-um |
| Era | Cenozoic — Neogene |
| Classification | Mammalia, Perissodactyla, Chalicotheriidae |
| Diet | Herbivorous |
| Height | 2.5 meters (8 feet) |
| Weight | 1,500 kilograms (3,300 pounds) |
| Location | Europe, Asia, and North America |
The Chalicotherium is one of the most bizarre prehistoric mammals.
It looked like a hybrid between a ground sloth and a horse and was one of the largest land mammals of Miocene Eurasia and Africa.
The Chalicotherium had two long forelimbs, while the hindlimbs were shorter and stout.
One of the most distinctive attributes of this large mammal was its long claws that had to be folded backward when the animal walked.
Only the forelimbs had these long claws, which means the Chalicotherium walked on its knuckles.
13. Megacerops
| Name | Megacerops |
| Name Meaning | “Large horned face” |
| Pronunciation | Meg-ah-seh-rops. |
| Era | Cenozoic — Paleogene |
| Classification | Mammalia, Perissodactyla, Brontotheriidae |
| Diet | Herbivorous |
| Height | 2.5 meters (8 feet) |
| Length | 4.63 meters (15.2 feet) |
| Weight | 3.3 tons (7,200 pounds) |
| Location | North America |
Megacerops was a giant rhinoceros-like mammal that lived in North America during the Late Eocene Epoch.
It is considered a close relative of modern horses but was significantly bigger.
The Megacerops were as big as modern African elephants, which is the third largest land animal today.
It stood at a height of about 2.5 meters (8 feet) tall at the shoulder and weighed roughly three tons.
The name Megacerops means “giant horned face,” referring to the blunt Y-shaped horns on its snout.
12. Titanotylopus
| Name | Titanotylopus |
| Name Meaning | “Giant knobby foot” |
| Pronunciation | Tie-tuh-noh-tye-loh-puhs |
| Era | Cenozoic — Quaternary |
| Classification | Mammalia, Artiodactyla, Camelidae |
| Diet | Herbivorous |
| Height | 3.4 meters (11 feet) |
| Length | 5 meters (11.5 feet) |
| Weight | 2,485.6 kilograms (5,480 pounds) |
| Location | North America |
Long before they became the domesticated load-bearing desert vehicles that they are today, the ancestors of modern camels were significantly bigger.
One of the biggest of them all was the Titanotylopus.
This was a giant camel that lived in North America during the Pleistocene.
It was the last of the prehistoric camels of North America to go extinct.
Titanotylopus stood at a shoulder height of more than 3.4 meters (11 feet) and weighed up to 2,485.6 kilograms (5,480 pounds).
11. Diprotodon
| Name | Diprotodon |
| Name Meaning | “Two forward teeth |
| Pronunciation | dye-PROH-toh-don |
| Era | Cenozoic — Quaternary |
| Classification | Mammalia, Diprotodontia, Diprotodontidae |
| Diet | Herbivorous |
| Height | 1.8 meters tall |
| Length | 4 meters (12 feet) long |
| Weight | 2,700 kilograms (about 3 tons) |
| Location | Australia |
The common name of the Diprotodon is giant wombat because it is closely related to modern wombats.
This massive mammal is the largest marsupial to have ever lived, with an estimated weight of up to three tons.
It lived in Australia during the Pleistocene Epoch and is the first fossil mammal to be discovered on the continent.
Diprotodon was a giant wombat-like marsupial that lived in Australia during the Pleistocene Epoch.
They lived in large herds that made seasonal migrations across the Australian continent in search of food and water.
10. Glyptodon
| Name | Glyptodon |
| Pronunciation | GLIP-toh-don |
| Era | Cenozoic — Quaternary |
| Classification | Mammalia, Cingulata, Chlamyphoridae |
| Diet | Herbivorous |
| Height | 1.2–1.5 meters (4–5 feet) |
| Length | 3–4 meters (10–13 feet) |
| Weight | 1,500–2,000 kilograms (3,300–4,400 pounds) |
| Location | North and South America |
The Glyptodon is the prehistoric ancestor of modern armadillos but was significantly bigger.
It weighed up to two tons, about the same size as a small car.
Like living armadillos, the Glyptodon had a giant dome-shaped shell that protected it from predators.
Other parts of this giant armadillo’s body, such as the head and tail, were covered in hard armor as well.
Glyptodon was a herbivore with large claws that were probably useful for digging burrows or foraging for food underground.
9. Megatherium
| Name | Megatherium |
| Name Meaning | “Great beast” |
| Pronunciation | Meg-uh-theer-ee-uhm |
| Era | Cenozoic—Quaternary |
| Classification | Mammalia, Pilosa, Megatheridae |
| Diet | Herbivorous |
| Height | 2.1 meters (6 feet 11 inches) |
| Length | 6 meters (20 feet) |
| Weight | 4 tons (8,800 pounds) |
| Location | South America and North America |
Imagine a sloth as big as an elephant; that’s how big the Megatherium was.
Also known as the giant ground sloth or megathere, the Megatherium was a genus of ground sloth that lived in South America from the Pliocene to the Pleistocene Epoch.
It was the biggest sloth to have ever lived.
Standing on its hind legs, this sloth reached a height of up to six meters (20 feet) and weighed about four tons on average.
Megatherium was a herbivore.
It had large claws, which were effective for stripping the leaves off trees.
8. Zygophyseter
| Name | Zygophyseter |
| Name Meaning | “Yoke Fin Whale” |
| Pronunciation | Zye-go-fye-seh-ter |
| Era | Cenozoic — Tertiary |
| Classification | Mammalia, Artiodactyla, Physeteroidea |
| Diet | Carnivorous |
| Length | 6.5 to 7 meters (21 to 23 feet) |
| Weight | 3,500kg (7,600 pounds) |
| Location | Worldwide |
The Zygophyseter was a giant prehistoric mammal that lived in Earth’s prehistoric seas about 7.6 million years ago.
It was a sperm whale that grew to an average size of up to seven meters.
Zygophyseter was an apex predator in the Miocene seas.
It is also known as the killer sperm whale due to its similarities in hunting style with the modern-day killer whale (orcas).
The exact size of this giant whale isn’t known, but it is arguably one of the largest mammals ever based on its estimated length.
7. Elasmotherium
| Name | Elasmotherium |
| Name Meaning | “Laminated beast” |
| Pronunciation | Ee-laz-muh-THEER-ee-um |
| Era | Cenozoic – Quaternary |
| Classification | Mammalia, Perissodactyla, Rhinocerotidae |
| Diet | Herbivorous |
| Height | 2 meters (6.5 feet) |
| Length | 5 meters (16 feet) |
| Weight | 3.5–5 tons (7,000–10,000 pounds) |
| Location | Europe and Asia |
The Elasmotherium is also commonly referred to as the Siberian Unicorn due to the single large horn on its forehead.
Interestingly, no Elasmotherium fossil has been found with an actual horn, but the presence of a potentially massive horn is indicated by a circular dome on the rhino’s forehead.
This giant rhino was about the same size as a mammoth but weighed about five tons on average.
It is often depicted with woolly fur, an adaptation that would have helped the rhino survive in the cold, harsh ecosystem where it lived.
6. Basilosaurus
| Name | Basilosaurus |
| Name Meaning | “The king lizard” |
| Pronunciation | Bah-sil-oh-saw-rus |
| Era | Cenozoic — Paleogene |
| Classification | Mammalia, Artiodactyla, Basilosauridae |
| Diet | Carnivorous (Piscivorous) |
| Length | 15 to 20 meters (49 to 66 feet) |
| Weight | 5.8 tons (11,600 pounds) |
| Location | North America, Africa and Asia |
The Basilosaurus is one of the most famous whale ancestors that qualifies for this list of the biggest prehistoric mammals.
One of the most notable ones is the Basilosaurus, a large prehistoric whale that lived in the ancient Tethys Sea during the Eocene Epoch.
With an estimated weight of roughly six tons, Basilosaurus was one of the largest animals of the Paleogene.
The Basilosaurus had a reptile-like body, so its fossils were initially misidentified as that of a marine reptile.
This giant mammal was a top predator in the Paleogene waters.
It preyed on fish, sharks, and other marine mammals in its ecosystem.
5. American Mastodon
| Name | Mastodon (Genus Mammut) |
| Name Meaning | Beast tooth |
| Pronunciation | MAS-tuh-don |
| Era | Cenozoic — Quaternary |
| Classification | Mammalia, Proboscidea, Mammutidae |
| Diet | Herbivorous |
| Height | 3.5 meters (11 feet) |
| Length | 4.5 meters (14.7 feet) |
| Weight | 8–11 tons (17,600–24,000 pounds) |
| Location | North America |
The American Mastodon was a large elephant-like mammal that lived in North America during the Pleistocene Epoch.
Some individuals lived until about 11,000 years ago, making them the most recent prehistoric elephants.
The mastodon had a typical elephant-like build but with a more robust appearance compared to modern elephants.
They lived in forests and woodlands and were predominantly high-browsing herbivores.
Fossils of the mastodon were discovered as far back as the 18th century, but scientists initially thought they were mammoth bones.
The mastodons were recognized as a distinct group in the early 19th century.
4. Steppe Mammoth
| Name | Mammuthus |
| Name Meaning | “Earth horn” |
| Pronunciation | Mam-mu-fus |
| Era | Cenozoic — Quaternary |
| Classification | Mammalia, Proboscidea, Elephantidae |
| Diet | Herbivorous |
| Height | 4.5 meters (14.8 feet) |
| Length | 7 meters (23 feet) |
| Weight | 10–14 tons (20,000–28,000 pounds) |
| Location | Africa, North America, Eurasia |
The mammoths were a group of large elephant-like mammals alive in North America and Eurasia during the Pleistocene Epoch.
The group includes a large number of well-known species, all known for their extremely long and curved tusks.
The largest of them was the Steppe Mammoth (Mammuthus trogontherii or M. armeniacus), which is considered the ancestor of later forms like the wooly mammoth and Columbian mammoth.
Mammoths were herbivores, but their diet depended on the specific plants that were most abundant in their ecosystem.
3. Deinotherium
| Name | Deinotherium |
| Name Meaning | “Terrible Beast” |
| Pronunciation | Dy-noe-fee-ree-um. |
| Era | Mesozoic – Late Cretaceous |
| Classification | Mammalia, Proboscidea, Deinotheriidae |
| Diet | Herbivorous |
| Height | 3.63–4.0 m (11.9–13.1 ft) |
| Length | 120–130 cm (47–51 in) |
| Weight | 8.8–12 tonnes (8800-12000 kgs) |
| Location | Africa, Asia, Europe |
Deinotherium was a massive elephant-like mammal that lived in Africa, Eurasia, and North America during the Miocene to Pleistocene epochs (about 23 million years ago).
It weighed about 13 tons and had an elephant-like build.
However, the limbs of the Deinotherium were proportionally longer and more gracile compared to those of modern elephants.
The two long tusks of this elephant curved downwards because they grew from the lower incisors (instead of the upper incisors, as seen in modern elephants).
Each tusk was up to four feet long.
2. Paraceratherium
| Name | Paraceratherium |
| Name Meaning | “Near horn beast |
| Pronunciation | Pa-ra-cee-ra-fee-ree-um |
| Era | Cenozoic — Quaternary |
| Classification | Mammalia, Perissodactyla, Hyracodontidae |
| Diet | Herbivorous |
| Height | 4.8 meters (15.7 feet) |
| Length | 7.4 meters (24.3 feet) |
| Weight | 15–20 tons (33,000–44,000 pounds) |
| Location | Central Asia |
The Rhino is one of the biggest land animals today, but it had an even bigger ancestor that currently holds the title of the largest terrestrial mammal to have ever lived.
The Paraceratherium was a 20-ton prehistoric rhinoceros that lived during the Oligocene (about 33 million years ago).
It looked considerably different from present-day rhino because it had a much longer neck and relatively long, slender legs.
Unlike modern rhinoceros, the Paraceratherium also had no horns.
The giraffe-like build of this prehistoric rhino suggests that they were high browsers, feeding from leaves at the top of tree canopies.
1. Livyatan
| Name | Livyatan |
| Name Meaning | “Derived from Hebrew mythology” |
| Pronunciation | Li-vy-a-tan |
| Era | Cenozoic — Neogene |
| Classification | Mammalia, Artiodactyla, Physeteroidea |
| Diet | Carnivorous |
| Length | 13 to 17 meters (42 to 56 feet) |
| Weight | 57 tonnes (125,663 pounds) |
| Location | Peru (South America) |
This 57-ton sperm whale is arguably the biggest prehistoric mammal to have ever lived.
An ancestor to modern sperm whales, the Livyatan is about the same size as its modern relative.
It is one of the biggest marine predators to have ever existed.
The Livyatan is also famous for its unique dentition.
This giant whale has the largest biting teeth of any known animal, with each one measuring about 36 centimeters (1.19 feet).
It was an apex predator with an appetite for sharks, marine mammals, and other large prey present in its habitat.
Sources:
- https://www.amnh.org/exhibitions/extreme-mammals/meet-your-relatives/indricotherium
- https://en.wikipedia.org/wiki/Mammoth
- https://en.wikipedia.org/wiki/Mastodon#o
- https://www.nhm.ac.uk/discover/news/2018/november/the-siberian-unicorn-lived-at-the-same-time-as-modern-humans.html
- https://www.amnh.org/explore/news-blogs/on-exhibit-posts/andrewsarchus
- https://en.wikipedia.org/wiki/Macrauchenia
- https://en.wikipedia.org/wiki/Barylambda
- https://en.wikipedia.org/wiki/Archaeoindris
- https://www.livescience.com/56795-bear-dog.html
- https://www.britannica.com/animal/Chalicotherium
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