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An inexact science -

The process of declaring an animal extinct is tricky, as it's often a bit of a guessing game. An endangered species is usually tracked as much as possible, but how do researchers know that they've truly lost the very last one?

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Parameters for declaring extinction -

Before 1990, a species could be declared extinct if 50 years had passed without a sighting. Nowadays, other factors are taken into account when deciding how likely it is that a species is extinct, such as the number of breeding adults, geographic range, and degradation of its habitat. There must be “no reasonable doubt that the last individual member has died.”

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A history of happy accidents -

Regardless of the measures in place, on rare occasions they get it wrong (and surely they've never been so happy to be wrong!). There have been numerous cases of animals believed to be long extinct suddenly reappearing.

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Coelacanth -

The coelacanth made the most impressive comeback in the history of the animal kingdom! This large fish was thought to have gone extinct along with the dinosaurs more than 60 million years ago, until it suddenly showed up off the coast of South Africa in 1938.

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Coelacanth -

The coelacanth is believed to be an important puzzle piece in the development of terrestrial animals. It has unique lobe fins that resemble legs and rotate in a rhythm similar to a trotting horse. This prehistoric marvel lives in deep underwater caves in the Indian Ocean and is still an endangered species.

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Takahe -

This fabulously colorful flightless bird used to roam free in what we now call New Zealand. It was declared extinct in 1898 due to hunting, predators, and habitat loss. However, a full 50 years after its "extinction," a colony of takahes was discovered high up in the Murchison Mountains in southern New Zealand.

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Takahe -

The country worked hard to save the species and the takahe became the focus of New Zealand's longest-running conservation program. The population of these beautiful birds has increased over the decades and they now thrive in multiple locations, including seven different islands off the mainland.

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Pygmy tarsier -

This wide-eyed little primate was thought to be extinct by the 1920s. These sensitive creatures are nocturnal and struggle to survive in captivity. Tarsiers have been known to try and take their own lives by banging their heads against the bars of their cages when confined.

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Pygmy tarsier -

The delicate pygmy tarsier was rediscovered when Indonesian scientists found one caught in a rat trap in 2000. Unfortunately, the trap killed the animal, but they found the first living ones in 2008.

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Tarsiers -

There's still a lot scientists don't know about these miniature jumping primates. Two previously unknown species were discovered as recently as 2017. The newly named Gursky's spectral tarsier is pictured here.

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Omura’s whale -

This large whale had a harder time than most animals convincing conservationists that it had disappeared! Omura's whale was first discovered in 2003, but scientists only found dead specimens and believed that it was already extinct. A decade later, a small group of Omura's whales was found living off the coast of Madagascar.

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Omura’s whale -

These whales are uniquely elegant swimmers thanks to their streamlined forms. Unlike other whale species, they never migrate and prefer to stay in their corner of the Indian Ocean, where conservationists keep a close eye on them.

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Somali elephant shrew -

With the body of a mouse and an extended elephant-like nose, it's easy to see where this little creature got its name. Scientists lost track of the Somali elephant shrew in the 1970s, believing it to be extinct, but the locals never agreed.

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Somali elephant shrew -

In 2019, a scientific expedition to the Horn of Africa led to the rediscovery of the shrew. They set out over 1,000 traps laden with peanut butter and oats, and spotted 12 Somali elephant shrews.

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Caspian horse -

The Caspian horse was a breed depicted in ancient Persian art, but it hadn't been seen for thousands of years, giving it a semi-mystical reputation. In 1957, an American horse breeder named Louise Laylin moved to Iran to marry a Persian prince and set up a riding school there.

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Caspian horse -

Laylin found the local horses too volatile, so she embarked on a mission to find the mystical Caspian horse. She traveled to the remote Caspian mountain where she found three of the horses she was looking for, and brought them back to breed. Today, there are sustainable populations of Caspian horses all over the world. They have a reputation for being calm and gentle with beginners.

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Santa Marta sabrewing -

The Santa Marta sabrewing is a rare kind of hummingbird endemic to the Sierra Nevada de Santa Marta of northeastern Colombia. It was declared critically endangered in 1946 and was only spotted once more in the 20th century, leading scientists to believe it was extinct.

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Santa Marta sabrewing -

However, a lucky birdwatcher spotted a Santa Marta sabrewing out of the blue in 2010. But the mysterious little birds are just about hanging on as their habitat continues to shrink.

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Wallace’s giant bee -

In 1859, Alfred Russell Wallace discovered the largest bee in the world in Indonesia and promptly named it after himself, as one does. Wallace’s giant bee was thought to be extinct until more specimens were found in 1981 and put in museums.

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Wallace’s giant bee -

They went quiet again after that, but in 2019 a group retraced Wallace's steps through Indonesia in the hopes of finding the species of bee still alive, and managed to lay eyes on one living example.

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Sierra Leone crab -

The distinctive Sierra Leone crab had not been sighted since 1955, and was believed to be extinct. But in 2021, a researcher named Pierre Mvogo Ndongo traveled to Sierra Leone and spent three weeks searching for the crab. He managed to find six of them with the help of the local people. The crabs had migrated inland away from water sources and adapted to breath air.

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Black browed babbler -

Prior to its miraculous rediscovery in 2020, this beautiful little bird was only observed by scientists once in the 1840s. It then disappeared for around 170 years, before two locals reported sightings in the forest of South Kalimantan in Indonesia.

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Chapman’s pygmy chameleon -

This tiny chameleon, which measures around 2.2 inches (5.5 cm), was spotted for the first time in the Malawi rain forest in 1992 and promptly disappeared. In the following decades, nearly 80% of the Malawi rain forest was destroyed, and Chapman’s pygmy chameleon was believed to have been lost along with it. Incredibly, the persistent lizard survived and was spotted again in 2016.

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Fernandina giant tortoise -

The species of giant tortoise called chelonoidis phantastica disappeared more than a century ago and was long believed to be extinct. But in 2019, 112 years after the last sighting, researchers came across a single female tortoise. She was found living on Fernandina Island in the Galápagos, which is how she got her name. She is the only living example of her kind, as far as researchers know.

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De-extinction -

The examples we've seen so far are of animals that were believed to be extinct, but were in fact quietly surviving away from prying eyes. Sometimes animals come back from the brink in a more controversial way. De-extinction, also rather dramatically known as resurrection biology, refers to the process of generating an organism that was truly extinct. Cloning is the most common method that scientists are working on.

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Pyrenean ibex -

The Pyrenean ibex, a subspecies of the Spanish ibex (pictured), is the only 'successful' case of de-extinction scientists have achieved through cloning. Tissue samples were taken from the final living Pyrenean ibex in 1999, and when she died, a clone was made by implanting nuclei from her cells into a goat egg, which they then used to impregnate more than 200 goats.

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Pyrenean ibex -

Only one of the baby ibex lived to term, but was born with a lung defect and died within minutes of its birth. This was still seen as a great triumph and is considered to be the first true de-extinction.

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Aldabra rail -

The Aldabra rail, or white-throated rail, is an example of iterative evolution. This is another process that could be considered de-extinction, although this one is natural. It occurs when a species goes extinct, but another species evolves over time to become exactly like the one that died out.

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Aldabra rail -

The Aldabra rail was a flightless bird that went extinct 136,000 years ago. An almost identical species emerged 100,000 years ago. Sea levels dropped, which allowed the species of bird to become flightless again, resulting in the Aldabra rail 2.0, as it were. 

Sources: (RTÉ) (Listverse) (Forbes) (Discover Magazine) (Petpedia)

See also: Facts about cloning and its controversy

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