The 7 Weirdest Extinct Animals 

Depiction of a Tully Monster in water

Written by Rebecca Mathews

Updated: October 9, 2023

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Over millions of years, animal species have evolved, lived, and died out. Some were huge, some were tiny, and some were beautiful, but some were a bit weird too! Here are the 7 weirdest extinct animals. Which one tops your list of weird?

1. Giant Sloth (Megatherium americanum)


Giant sloths were 20 feet long and had 7-inch claws.

©Esteban De Armas/

Today’s sloths are tree-dwellers about the size of a small dog. However, from the middle Pleistocene to the Holocene era, an enormous sloth lived in caves and stripped tree branches with 7-inch claws. The giant sloth had a pointed face and a prehensile tongue it could wrap around leaves. It weighed a massive 4 tons and, from nose to tail, was 20 feet long!

There were at least 23 species of giant sloth, but the largest found so far was Megatherium Americanum, “The great beast from America.” They were so large they had very few predators. Massive dire wolves and cave bears may have hunted young or elderly sloths, but the largest were safe until climate change altered their environment.

Paleontologists think the melting ice sheets changed their wood, grassland, and river environments so quickly it was impossible to adapt in time. This period coincided with the arrival of humans, who likely hunted them for meat and skins.

It’s almost impossible to imagine what this animal looked like, and it’s one of the weirdest extinct animals to ever roam the planet.

2. White-Footed Rabbit-Rat (Conilurus albipes)

White-Footed Rabbit-rat (Conilurus albipes)

The last white-footed rabbit rat was seen in 1845, but reports persisted until the 1930s.

©John Gould, et al / public domain – Original / License

The weirdest extinct animals have the weirdest names. Have you ever heard of the white-footed rabbit rat?

This extinct weird creature was a rodent related to rats, mice, and squirrels. It was endemic to Australia’s woodlands from Sydney to Adelaide. It looked like a squirrel but had a two-colored bushy tail. Its coat was dark brown with a white belly and white feet. It weighed around 7.5 ounces and up to 10 inches in length, and its fluffy tail was another 10 inches.

It was reportedly a pretty creature, but because it raided settlers’ grain stores and was thought to spread disease, it was hunted by humans and their domestic cats and dogs. Settlers also destroyed their habitats by clearing forests and eucalyptus trees for farmland. The last one was seen in 1845, but reports persisted until the 1930s.

3. Basilosaurus

Basilosaurus cetoides fossilized skull

Basilosaurus was a 66 feet long predatory carnivorous whale that went extinct 40 million years ago.


Basilosaurus: It means ‘king lizard,’ so we expect to find a dinosaur similar to T-rex, but wait! The basilosaurus was actually a huge predatory whale.

About 40 million years ago, in the late Eocene era (they came after the dinosaurs were wiped out), whale ancestors lived on land. Some genera moved to the oceans, and basilosaurus became an apex predator that ate fish and sharks. Experts think they also took large mammals such as prehistoric elephants from the shoreline.

So far, paleontologists have found two species: Basilosaurus cetoides and Basilosaurus isis. Both were up to 66 feet long and lived in the Tethys Ocean, and that body of water is now called the Atlantic and Indian oceans.

Basilosaurus skeletons are found in America, and they died out around 35 million to 33.9 million years ago when other prehistoric animals went extinct. Experts think there may have been a lot of volcanic activity, climate change, or even another meteor impact then.

Luckily for sailors, basilosaurus has no living descendants. In contrast to today’s gentle whales, basilosaurus seems like a horror story character, but it was real and surely one of the weirdest extinct animals.  

4. Tully Monster (Tullimonstrum)

Scientists are unraveling the tully monster’s secrets from fossil records and think it was an ancient fish similar to lampreys.

©Dotted Yeti/

The tully monster was so weird that it even left expert paleontologists confused.

It was a worm-like creature about a foot long with eyestalks and a pincher-tipped proboscis with razor-sharp teeth.

In 1958 a fossilized Tully monster was found in Mazon Creek, Illinois, in 300-million-year-old rock. Scientists are unraveling its secrets from fossil records and think it was an ancient fish similar to lampreys. Lampreys are jawless blood-sucking fish that attach themselves to other fish and leech their blood.

The Tully monster is still hotly debated. This article in the journal Nature suggests it had vertebrae, but other scientists disagree. It’ll keep palaeologists busy for at least another 50 years.  

5. Arthropleura

Arthropleura were most likely isopods similar to woodlice.


The weirdest extinct animals create nightmares, and the arthropleura is a genus of creatures from the darkest imaginations. They were six to eight-foot-long millipede-like creatures and the biggest arthropods ever.

Bugs grew to huge sizes in the Paleozoic period. Scientists aren’t sure why but theorize their size was due to more oxygen in the atmosphere and few predators. It would take a brave predator to tackle an eight foot long insect! It’s the stuff of nightmares, but arthropleura were most likely isopods similar to woodlice. The most probable theory is that they scuttled around woodland floors eating decomposing wood and carrion.

It’s not certain because arthropleura lived 300 million years ago, and evidence is thin on the ground.

Sleep well!

6. Josephoartigasia Monesi

Josephoartigasia monesi

Josephoartigasia monesi were giant rodents as big as horses.

©Andrés Rinderknecht & Ernesto Blanco; Illustration: Gustavo Lecuona / CC BY-SA 2.5 – Original / License

Introducing the largest rodent to grace the planet: Josephoartigasia monesi.  

There were two species of giant rodent in the Dinomyidae family, the J. monesi and J. magna. They lived in the middle to the early Pleistocene era in modern South America.  

Josephoartigasia monesi was a huge rodent the size of a horse. It weighed 2,200 pounds, was nearly 9 feet long, and stood just under 5 feet tall. Its front teeth were 10 inches long, and experts think they used them to dig for roots, like elephants’ tusks. It’s also possible they defended themselves against saber-tooth tigers and terror birds.

Using fossilized skulls, experts have estimated its bite force at three times that of today’s lion! As weird and terrifying as it must have looked, this extinct animal most likely lived near rivers in forested areas and ate aquatic vegetation.

Its closest living relative is the rare pacarana rodent that’s native to South America. It is much smaller and not nearly as weird.

7. Titanoboa (Titanoboa cerrejonensis)

Experts aren’t sure why the titanoboa became extinct but attribute it to colder conditions brought on by climate change.

©Dotted Yeti/

Titanoboa is an extinct type of mega-snake genus from modern-day northeastern Columbia. Snake phobics will be pleased to hear it’s been extinct for 60 million to 58 million years.

Titanoboa cerrejonensis was a massive snake up to 42 feet long (that is not a typo!) with a 16-inch skull and weighed 2,500 pounds. It’s the largest snake ever discovered. In comparison, our largest modern snakes, such as the green anaconda, only reach 30 feet and weigh 550 pounds.  

At first, paleontologists thought Titanoboa ate the same diet as anacondas, but recent research challenged this. Its fossilized teeth indicated it was more likely to prey on fish. This theory is supported by its warm and humid tropical rainforest and river environment.

Experts aren’t sure why this boa constrictor-like snake became extinct but attribute it to colder conditions brought on by climate change.

Perhaps not so much weird, but terrifying!

Summary of the 7 Weirdest Extinct Animals 

Here’s a recap of the 7 strangest animals that (thankfully, in some scary cases!) no longer walk the Earth:

NumberAnimalWeird Features
1Giant SlothWeighed 4 tons, measured 20 feet long, and had 7-inch claws
2White-Footed Rabbit-RatOddly named rodent related to rats, mice, and squirrels
3BasilosaurusHuge predatory whale that grew up to 66 feet long
4Tully MonsterWorm-like creature about 1 foot long with eyestalks and a pincher-tipped proboscis with razor-sharp teeth
5ArthropleuraMillipede-like creature that was 6 to 8 feet long
6Josephoartigasia MonesiHuge rodent the size of a horse that was 2,200 pounds, nearly 9 feet long, and under 5 feet tall with 10-inch-long front teeth
7TitanoboaMassive snake up to 42 feet long with a 16-inch skull and weighing 2,500 pounds

Bonus Weirdest Extinct Animal: Smooth Handfish (Sympterichthys unipennis)

Handfish walk on the shallow ocean seafloor with four hands which are their pectoral and pelvic fins.


This cute, weird fish is possibly extinct, but it’s not confirmed. It was declared extinct in 2020, but in 2021 was changed to “data deficient,” meaning experts don’t have enough information to decide if it’s truly extinct.

Let’s hope not because the smooth handfish is very weird!

Endemic to Tasmania’s coast the smooth handfish was first discovered in 1802 — and that’s it! No other individuals have been spotted, and the original smooth handfish is in Paris’s Natural History Museum.

Handfish walk on the shallow ocean seafloor with four hands that are their pectoral and pelvic fins. There are 13 other types of handfish alive today, such as the spotted handfish, but all species are extremely rare.

The smooth handfish is only known from the original specimen. It had bulging eyes, spiky fins, and a mohawk-like spike on its forehead. It probably ate small shellfish, worms, and crustaceans. It’s thought that intensive bottom-trawling for scallops and oysters in the 19-20th century destroyed their habitats.

Extinct or not? It doesn’t look good for the smooth handfish. Extensive surveys by divers haven’t uncovered a single specimen. It’s been 200 years since anyone saw a live smooth handfish.

The weirdest extinct animals are fun to read about and imagine, but their extinction is more serious. Climate change, environmental destruction, and hunting have wiped out animal species, and it’s a worrying trend.

What Animals Are in Danger of Extinction?

Bull elephant, loxodonta africana, in the grasslands of Amboseli National Park, Kenya. Front view.

Earth’s largest land mammal, the


, is in danger of extinction.

©Jane Rix/

As we’ve discovered, some really strange animals have gone extinct on Earth in ages past. Unfortunately, there are a lot of animals under threat of extinction today. Overall, the IUCN has listed 5,766 different animal species as endangered. The criteria for a species to be added to the endangered list are as follows:

  • Population reduction–A taxon’s population is reduced by 50-70% due to certain factors defined by the IUCN
  • Geographic Reduction–The specie’s extant area is reduced to between 5,000 and 500 square kilometers
  • Dangerously low number of adults–A taxon’s population only has 2,500 or fewer adults left
  • Expected rapid decline

Below is a list of three of the largest animal species today that are facing extinction:

1. African Savannah (Bush) Elephant/African Forest Elephant/Asian Elephant 

Elephants are the largest land mammals on Earth, and unfortunately, they are facing extinction. African forest elephant numbers have declined by over 86% in the past 31 years, while African savanna elephants have decreased by 60% over the last 50 years. Both cases have resulted from poaching and habitat loss. Meanwhile, Asian elephants are endangered due to habitat loss, fragmentation, and poaching. There are only an estimated 30,000 to 50,000 left in the wild. Currently, both African savannah and Asian elephants are listed as endangered, while African forest elephants are critically endangered. 

2. Bengal Tiger/Siberian Tiger/Sumatran Tiger/Indochinese Tiger/Malayan Tiger/South China Tiger

Tigers are the largest cat species on the planet, but all 6 extant species are either endangered or critically endangered. Three species have gone extinct in the last 100 years: the Javan tiger (1970s), Bali tiger (1930’s), and Caspian tiger (2003). Tigers have faced the largest threat due to habitat loss and poaching (for their exotic coats, and in some places, consumption and use of other body parts for rituals, jewelry, and more). 

3. Blue Whale

Blue whales are the largest animals on the earth, inhabiting the planet’s oceans. They were hunted in the past for their meat and blubber, to the point that their numbers dropped from an estimated 200,000 in the 1800s to 20,000 today. They are listed as endangered by the IUCN. Currently, their greatest threat is global warming. 

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About the Author

Rebecca is a writer at A-Z Animals where her primary focus is on plants and geography. Rebecca has been writing and researching the environment for over 10 years and holds a Master’s Degree from Reading University in Archaeology, which she earned in 2005. A resident of England’s south coast, Rebecca enjoys rehabilitating injured wildlife and visiting Greek islands to support the stray cat population.

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