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EXTINCTION

KEVIN APAGWON AKANLAGM

More than 99% of all species that ever inhabited the Earth are extinct.

Extinction is the termination of a taxon or species as a result of the death of the last member. Other zoologist go the extra mile to define extinction as the inability of a taxon or species to ensure its continuity; in the sense that individuals of the species left behind are unable to reproduce due to poor health, age, sparse distribution over a large range or lack of active sexual activity. The exact moment of extinction is generally considered to be the demise of the last individual of the species although the capacity to breed and recover may have been long lost before then.

Notable extinct species include the; non avian dinosaur, dodo, smilodon or sabre-toothed cats, West African black rhinoceros, Baiji White dolphin, Pyrenean Ibex, ground sloths, golden toads, thylacine or Tasmanian tiger, tribolites, Passenger pigeon, Stellers Sea cow, Great Auk, woolly mammoth among others.

Dinosaurs – fearfully great lizards

In 1841, English naturalist, Sir Richard Owen coined the term “Dinosauria" from Greek words, “deinos" meaning fearfully great and “saurus" meaning lizards. Well, sorry to burst your bubble, but dinosaurs are not lizards, far from it. Instead, they are much closer to birds. Birds share over a hundred distinct anatomical features with dinosaurs and thus are generally accepted to be their closest living relatives. Majority of palaeontologist reject the traditional style of taxonomy and consider birds as dinosaurs. Conclusively, they split dinosaurs into two classes; avian and non-avian dinosaurs implying that avian dinosaurs are not yet extinct. Dinosaurs first appeared during the Triassic period between 243 and 233 million years ago and died out in the Cretaceous period between 145 and 65 million years ago. Dinosaurs lived on all seven continents and were wiped out during the Cretaceous - Paleogene mass extinction event, the fifth and most recent mass extinction event, in which 75% of all life became extinct leaving birds as the only extant dinosaurs on Earth. Everything over 10 kilograms at that time became extinct.

Dinosaurs. Tyrannosaurus and Triceratops. (Left to Right)

Woolly Mammoth

An enormous land creature believed to be closely related to the modern-day elephant. It was over 4 meters tall and weighed over 6 tons. They were entirely covered with fur and only their curved tusks could be easily up to 5 metres long! They became extinct over 10,000 years ago through a combination of habitat degradation, climate change and hunting by humans. The last mammoth is believed to have disappeared from Wrangel Island in the Artic Ocean around 1,700 BC.

Woolly Mammoth

Dodo

A large flightless bird that inhabited Mauritius. The only account we have of the Dodo's appearance is from writings and illustrations from the late 17th century. Presumably, the dodo became flightless due to the availability of abundant food and a relative absence of predators. The bird was hunted to extinction by sailors and their domesticated pets.

Dodo

Tasmanian tigers

Totally unrelated to modern-day tigers, Tasmanian tigers resembled medium-to-large sized dogs with a nose-tail length of 2 metres. The last wild Tasmanian tiger was killed between 1910 to 1920, with the last captive one dying in 1936.

Tansmanian Tiger

Sabre-toothed cat

They existed between 55 million and 11,700 years ago. They were untamed carnivores named after their elongated canines which were almost 50 cm long. They were believed to be top-notch hunters and could open their jaws to a whooping 120 degrees – more than twice as wide as the modern-day lion! Their extinction, once again could be linked to competition with humans.

Sabre-toothed cat (head)

Steller’s Sea Cow

Named after famous naturalist George Steller after he discovered the creature in 1741, Steller’s Sea Cow is an enormous tame herbivore and spent majority of its time eating kelp. This creature had had very short and sad story. Within just 27 years of its discovery by Europeans, it was hunted to extinction. This is likely attributed to its large and conspicuous nature and its inability to submerge itself wholly.

Steller’s Sea Cow

Pyrenean Ibex

Also known as the Iberian or Spanish goat, they were historically believed to number approximately 50,000. But by the early 1900s, its numbers had fallen to almost a 100. The exact reason of its extinction is unknown but most likely attributed to poaching and its inability to compete with other mammals for food and habitat. The last known Pyrenean Ibex was killed by a falling tree in northern Spain in the early 2000s.

Pyrenean Ibex
Pyrenean Ibex

It is also very likely that some of the aforementioned animals are not functionally extinct yet and are just missing. The phenomenon – Lazarus taxa refers to the event where a species abruptly re-appears after been presumed extinct. The Coelacanth, either of the two species of deep water fish, Latimeria chalumnae of the Indian Ocean and Latimeria menadoensis of Indonesia has been thought to be extinct since the end of the Cretaceous period (for 70 million years). In 1938 however, a living specimen was found on the east coast of South Africa.

Coelacanth 

The Lord Howe Island stick insect also known as Dryococelus australis was assumed to be extinct in 1930. In 2001 however, an expedition manage to locate 24 living specimen. They were transported to Melbourne Zoo and by 2012, 9000 descendants were reintroduced into the wild.

Lord Howe Island Stick Insect

Causes of extinction

1.   Habitat Degradation : This is the main anthropogenic cause of species extinction. This may occur directly by the habitat becoming toxic and impossible to survive in or indirect by limiting a species ability to effective compete with others for survival. The golden toad became extinct due to the widespread destruction on the tropical rainforest.

2.   Predation / Competition / Disease: Some species were hunted out of existence by their predators or their inability to compete with other species they shared their habitat with. Human populations may themselves act as invasive predators. Diseases might also have also had a role in wiping out certain species from existence.

3.   Co-extinction (extinction of a keystone species): Extinction of a species due to the extinction of another species(the keystone species) which it closely depends on for survival. Co-extinction can also occur when a species loses its pollinator or its prey. An example is the extinction of the Haast Eagle because its prey, the moa, a large flightless bird became extinct.

4.   Climate change: Changes in temperature, rainfall patterns, heatwaves, desertification, rising tides among others have led to the extinction of numerous species.

5.   Planned extinction: The smallpox virus and rinderpest virus have been made extinct in the wild by the human race because of their deadly effects on man and cattle respectively.

6.   Mass extinction events: In the last 500 million years, life has had to recover from five mass extinction events. They are in order of occurrence the; Ordovician – Silurian (443 million years ago), The late Devonian (372 million years ago), Persian – Triassic (252 million years ago), Triassic – Jurassic (201 million years ago) and  Cretaceous – Paleogene (66 million years ago) mass extinction events.

Mass Extinction Events

Holocene extinction

We are currently in the midst of Earth's sixth mass extinction event and it's accelerating, being fuelled by humanity’s doings. Known as the Holocene extinction, this event has been occurring for the last 10,000 years, beginning at the end of the last ice age. But an increasing human population and a warming planet have only made this mass extinction even more dire. The Holocene may yet be the most serious environmental threat to the persistence of civilization, because it is irreversible. A renowned biologist, E. O. Wilson estimated that if the current rate of human destruction of the biosphere continues, one-half of all extant species of both flora and fauna on Earth would be extinct in a hundred years.

Extinctionism is the belief that only the extinction of humanity will lead to the recovery of the Earth's environment. True or not, we need to step up our game to save our dying planet. Future generations deserve better from us.

REFERENCES

1. Causes of extinction. Retrieved from https://www.thoughtco.com/reasons-animals-go-extinct-3889931

2. Holocene extinction. Retrieved from https://eowilsonfoundation.org/humans-are-speeding-extinction-and-altering-the-natural-world-at-an-unprecedented-pace/#:~:text=an 'Unprecedented' Pace-,Humans Are Speeding Extinction and Altering,World at an 'Unprecedented' Pace&text=The theory of island biogeography,of habitat available to them.

3. Images (Sabre-toothed cat, Coelacanth and Mass Extinction Events). Retrieved from https://www.nationalgeographic.com/