Although it may not be obvious, multiple signs point to the planet being in the middle of another mass extinction.

The animal population is decreasing at an alarming rate due to human activities like deforestation and mining. According to a report from the United Nations, the number of species threatened with extinction today could be close to one million, but that’s nothing compared to the number of species that have already been lost throughout the earth’s history.

Click through for facts about 15 animals that have already gone extinct.

First discovered in 1494, Caribbean monk seals were hunted for their blubber.

Caribbean monk seals were once the only native seal found in the Caribbean. They were frequently killed by hunters for their blubber following European colonization from the 1700s to the 1900s.

The species was listed as endangered in 1967 and declared extinct in 2008 after more than 50 years without a confirmed sighting. Kyle Baker, a biologist for the National Marine Fisheries Service, said: “Humans left the Caribbean monk seal population unsustainable after overhunting them.”

Despite their appearance in “Jurassic Park,” scientists believe Velociraptors were actually covered in feathers.

In “Jurassic Park,” the Velociraptor is portrayed as a large, intimidating dinosaur that’s out for blood. However, these movie creatures probably looked nothing like their real-life counterparts.

Aside from being the size of a big turkey, scientists say that velociraptors were also covered in feathers. “We know that for sure because we found specimens that have the insertion points for feathers on their arms.” Dr. Mark Norell, Chairman of Paleontology at the American Museum of Natural History, previously told Business Insider.

Elephant birds were enormous, flightless creatures that weighed over 1,000 pounds.

The ancient elephant birds walked the earth over 10,000 years ago. The 10-foot birds may have had small wings that were useless for flight, but they also weighed more than 1,000 pounds. Given the massive size of the creature, the eggs of elephant birds were believed to be the largest laid by any animal.

Scientists say that elephant birds were killed off after being hunted for food. Habitat loss due to deforestation also contributed to their decline.

The last dusky seaside sparrow died on Discovery Island, a nature reserve owned by Disney.

There were once thousands of dusky seaside sparrows living on the East Coast of Florida. When the bird started to die out due to pesticides and construction, conservationists at Walt Disney World’s nature reserve, Discovery Island, attempted to save the species through cross-breeding.

In 1987, Orange Band, the last known dusky seaside sparrow died in captivity, marking the end of the species.

The Dreadnoughtus was the largest land animal that ever lived.

The Dreadnoughtus was a long-necked dinosaur that lived 77 million years ago. It’s thought to be the largest land animal that ever lived, weighing 65 tons and reaching 85 feet tall with a 37-foot-long neck. For comparison, modern giraffes typically reach 18 feet tall.

The Irish elk had the largest antlers of any known deer.

The Irish Elk is an extinct species of deer that was once found across Europe and Asia. This giant animal had antlers that spanned 13 feet long, making them the longest antlers of any type of deer known.

It’s believed by scientists that the species went extinct during the ice age after starving to death.

The Tecopa pupfish had the ability to live in water temperatures of more than 100 degrees Fahrenheit.

The Tecopa pupfish got its name from where it lived, in the outflows of the Tecopa Hot Springs in California. Because of the fluctuating water temperatures, the Tecopa pupfish survived in water as cold as 50 degrees Fahrenheit and as hot as 108 degrees Fahrenheit.

The species was officially declared extinct in 1981 after Fish and Wildlife Service searched over 40 locations and found no trace of the animal.

The Ankylosaurus was a heavily armored dinosaur with a tail that could be used as a club.

Although it’s not the biggest or most ferocious dinosaur, the Ankylosaurus was covered in bony plates that served as armor against its predators, including the T.rex.

The Ankylosaurus’ tail ended with a bony ball that could be used as a club if provoked. Scientists have also proposed that the tail was used to attract mates.

Some woolly mammoths became trapped in ice, preserving their bodies.

The woolly mammoth went extinct more than 4,000 years ago, but that hasn’t stopped scientists from attempting to bring them back. Because these giants lived in Siberia, many of them became trapped in ice, which preserved their bodies. It’s reported that modern sled dogs have eaten thawed mammoth meat dating back over 30,000 years.

The Pyrenean ibex was briefly brought back from extinction.

After years of being hunted, the Pyrenean ibex went extinct in 2000 when a tree fell on the last known animal. Prior to its extinction, scientists retrieved its cells with the intention of cloning it. In 2003, the Pyrenean ibex was the first animal brought back to life from extinction. Unfortunately, the clone died minutes after birth.

The Tyrannosaurus rex only had a lifespan of around 28 years.

Arguably the most well-known dinosaur, the Tyrannosaurus rex lived during the Late Cretaceous period in North America, about 85 million to 65 million years ago. The largest T. rex ever found only lived to around 29 years old, which scientists determined through lines in its fossilized bones. The creature would have achieved adult size after 20 years.

Feral cats are believed to have contributed to the extinction of the Stephens Island wren.

The small, flightless Stephens Island wren lived on an island off the coast of New Zealand, before going extinct in 1895 due to land development and the introduction of cats to the area.

According to folklore, a cat named Tibbles moved to the island with her owner in 1984 and killed off the rest of the species. However, a report by the Ornithological Society of New Zealand suggests other feral cats contributed to the bird’s extinction.

The plates along the back of a Stegosaurus were likely used to regulate heat.

The Stegosaurus lived during the Jurassic period, 159 million to 144 million years ago, and is known for its spiked tail and plated back.

Scientists have had different theories as to the purpose of the plates, but new discoveries suggest they were used to regulate the dinosaur’s temperature. They could both collect heat from the sun to keep them warm, and release heat to keep them cool.

The elusive Kawekaweau, a species of gecko, was found more than 100 years after being declared extinct.

The kawekaweau was a brown gecko in New Zealand that hadn’t ever been seen or examined by scientists. It was said to reach up to two feet long, but scientists had no concrete evidence. The closest they had ever got was a biologist who heard a Maori chief describe killing a kawekaweau in 1870.

However, in 1986, researchers came across an unlabeled specimen in the basement of the Natural History Museum in Marseille, France, which was determined to be the kawekaweau.

The Carolina parakeet was the only species native to the eastern United States.

As the only parrot species native to the eastern United States, Carolina parakeets used to be prevalent from southern New York and Wisconsin to the Gulf of Mexico.

The last Carolina parakeet died in February 1918 at the Cincinnati Zoo, but the birds weren’t officially declared extinct until 1939. A combination of habitat loss, pest control, and humans using their feathers to adorn hats, contributed to the downfall of this species.